Star chart courtesy of the European Space Agency

The annual Perseids meteor shower reaches its peak this weekend, with 80-100 meteors per hour predicted before dawn on Monday 13th August.

Annual meteor showers occur when the Earth's orbit passes through the orbit of a comet. Dust that the comet has left behind is swept up by the Earth and burns up in its atmosphere. We see these tiny particles burning up as shooting stars in the night sky.

The Perseids meteor shower is a bright shower associated with comet Swift-Tuttle, which last passed close to the Sun in 1992. Perseid meteors can be seen during late July and early August, with a peak around the 12th of August. To best see the meteor shower, go outside after 11pm and look for the constellation Perseus in the northeast. In clear weather, you should be able to spot a meteor every few minutes or so. Most meteors are flashes of light lasting less than a second, but some may be more dramatic and leave more persistent trails.

More information about this meteor shower can be found in the Royal Observatory's Perseids fact file.

If you do see some meteors, please let us know by leaving a comment.

It seems like the Perseid meteors put on a good show on Sunday night. I saw a couple from my back yard, even against the bright lights of South East London.

Several people have posted photos of the Perseids on Flickr. Visit our Flickr favourites page to see a few that caught our eye, including the nice photo of a Perseid shown above.

The BBC has a round-up of comments about the Perseids from people around the UK.

This month we can see the planets Jupiter in the early evening and Mars just after midnight, and plenty of interesting objects in the Milky Way arcing overhead.

The word planet originates from the Greek meaning ‘wanderer’. As the planets orbit around the Sun, they slowly wander across the starry background. During September, Jupiter wanders slightly closer to the Sun, being visible in the west for 3 hours after sunset at the start of the month, but only for 2 hours by the month's end. Looking at Jupiter through binoculars, you can see up to four moons that orbit the planet.

Mars is also a wanderer, rising in the east earlier and earlier each day. During September, Mars is rising around midnight (BST). The bright red-giant star Aldebaran to the right of Mars, and the bright yellow star Capella above Mars, act as useful guides.

At this time of year, the Earth is on the side of the Sun which allows us to see constellations such as Hercules, Cygnus and Lyra, as well as the Summer Triangle directly overhead (see our star map).

In Cygnus, the star that makes up the head of the swan is called Alberio. Although it looks like a lone star to the unaided eye, a small telescope (or binoculars) reveals that this is actually a double star. It is the stark difference in colours that makes this double star such a delight! Although there has been no sign of any orbital motion in the last hundred years of observation, calculations suggest that they orbit around each other once every 70,000 years.

Close to Alberio, is the Dumbbell nebula – the remains of a dead star. At the centre of the Dumbbell is a faint white dwarf star, the left over core of a star that puffed out its outer layers to form the nebula. From observing the speed of expansion, the nebula is estimated to be about 11,000 years old. It is visible with a small telescope, some 1,300 light-years away.

In Lyra, another nebulae is visible through a small telescope – the ring nebula. Looking like a ring of smoke, it lies 1500 light years away. At the centre is a very hot white dwarf star emitting intense ultraviolet radiation, causing the ring to glow.

Visible towards the North West this month is the great globular cluster in the constellation Hercules. Through even a small telescope the sight is stunning. This cluster contains several hundred thousand stars! The cluster is about 25,000 light-years away, on the very outskirts of our own Milky Way galaxy

Look towards the North, and you can find the pattern of stars called the Plough (the tail and body of the great Bear, Ursa Major). The handle of the Plough points towards Arcturus, which can be remembered by the ditty “Follow the arc to Arcturus!”. Arcturus is a bright red-giant star, 16 times wider than our own Sun, and over 100 times brighter.

Happy observing!

The National Maritime Museum website has times for the visibility of the new crescent Moon, and the start of Ramadan, this week.

All of the objects mentioned in last month's guide are still visible throughout October.

However, Jupiter is getting increasingly difficult to observe, now setting just 2 hours after sunset. Look low towards the south-west about one hour after sunset, and it is the brightest object in the sky. Take a look through binoculars, and see if you can spot the four bright Galilean moons that orbit around the planet.

Although we are losing Jupiter until next year, we are gaining Mars, as it wanders across the sky to become more easily visible. By the end of October, Mars is rising in the east as early as 22:30 local time.

Be careful not to get Mars confused with the red giant star Aldebaran, which rises just one hour earlier. Just above Aldebaran is a small cluster of a few hundred stars called the Pleiades. The cluster is also known as the seven sisters, because the brightest seven are visible to the unaided eye within an area the same size as the full moon.

Aldebaran lies about 12 degrees below the Pleiades star cluster - that is the size of your out-stretched hand at arms length - while Mars is far off towards the bottom left of both in the evening eastern sky.

At midnight, another red giant star rises below Aldebaran and to the right of Mars - the bright red giant Betelgeuse.

Betelgeuse is part of the constellation of Orion - the classic winter constellation. Currently, Orion is rising at midnight, but by the end of November, it will have risen by 10pm, all thanks to the Earth moving around the Sun to get a better view of this wonderful constellation! More about Orion next month...

On October 23, Comet Holmes was a faint comet. A large and very expensive amateur telescope, located far away from light pollution, was required to catch even a glimpse of it. But just 24 hours later, it was almost a million times brighter, and easily visible with the unaided eye - even from London!

While the stars all appear as points of light in the night sky, the comet appears noticeably larger and more diffused, even with the unaided eye (although, the comet currently has no tail).

You can find Comet Holmes throughout the night in the constellation of Perseus. Click on the sky map for a larger version (generated with Stellarium); the red line indicates the plane of our solar system, also the path that the Moon approximately moves along.

For the latest details, see SpaceWeather.com, which also has a frequently updated photo gallery of the comet.

But what has happened to Comet Holmes? Why did it suddenly brighten so much? Maybe part of the surface of the comet has cracked, and the newly exposed (water) ice beneath has been heated by the Sun and turned into a gas that now surrounds the nucleus of the comet.

Comet Holmes was originally discovered in 1892 by Edwin Holmes in London. His discovery was confirmed within days here at the Royal Observatory Greenwich. Holmes managed to discover the comet through a very similar event to what is currently occurring. In 1892, it suddenly brightened allowing Holmes to spot it, and it remained visible to the unaided eye for another 3 weeks until it faded away. 75 days later the comet once again brightened to unaided eye brightness!

But what will happen this time? Currently, the cloud of gas that surrounds the comet (which is making it appear so bright) continues to increase in size. The comet now appears larger in the sky than Jupiter, and some suggest that the cloud could appear as large as the Moon – although, if it did, the outermost gas would not be bright enough for us to see with the unaided eye.

So why not pop outside and see if you can spot it yourself?

Look towards the north to find Ursa Major – the back half of which is known as The Plough in the UK, a very familiar set of seven stars. The two front stars of the Plough point upwards towards Polaris, which is always due north. Just to the right of Polaris is the constellation of Cassiopeia, easy to spot thanks to its "W" shape. As you pan down from Cassiopeia, look for a triangle of stars... although, the bottom left of the triangle is Comet Holmes!

There are lots of other interesting (red!) objects in that area of sky, too. If you look up at 11pm (local time), you will notice that the Earth has moved around the Sun enough so that we can once again see the constellation of Orion. Betelgeuse, a red supergiant star, is visible at the top-left of Orion.

To the top-left of Betelgeuse is the very bright Mars, and to the top-right is the red giant star Aldebaran. Above Aldebaran is the cluster of seven stars known as the Pleiades, about the same size as the full Moon, and a beautiful sight through binoculars.

Above Mars is yet another red star, Capella. And coming full circle, above Capella is Comet Holmes.

Comet Holmes is currently over the north of our solar-system, between the orbits of Jupiter and Mars, and is heading towards the extreme of its elliptical orbit.

Comet Holmes continues to be clearly visible to the unaided eye. See my previous post for details of where to look (it hasn't moved much in the last week or so).

For the latest photographs, some of which show a developing tail, see the SpaceWeather.com gallery (which is where we found the image to the left, by Vicent Peris and José Luis Lamadrid).

Even though the summer has long gone, we can still see the summer triangle!

The Sun is now setting so early that we are still able to see the constellations of Cygnus, Lyra & Aquila in the evening sky (see chart; click for a larger version) - and it is the brightest star in each of these constellations that make up the summer triangle. Although these constellations were directly overhead in the summer, they are now low down in the west, ducking beneath the western horizon at around 9pm. But they are still ideal for late afternoon or early evening observing.

The star that forms the head of Cygnus the swan is called Albireo, a blue and golden double star that is a beautiful sight through a small telescope. Notice how Cygnus is flying directly downwards, head-first into the western horizon! Just to the right of Albireo is the Ring Nebula in Lyra, the left over remains of a star that puffed out its outer layers to form the nebula some 1,500 years ago. And to the left of Albireo is the Dumbbell Nebula, another treat for small telescope owners.

Almost directly overhead, high in the east, is the easily recognisable W-shape of the constellation Cassiopeia (see chart, right; click for a larger version). Below Cassiopeia is Perseus, which contains the star Mirphak.

If you want to see a comet, look toward Mirphak. While all the stars are pin sharp, you will be able to see a fuzzy object just next to Mirphak - that is the incredible Comet Holmes! For more details about Holmes, see my previous posts. This is a rare opportunity to see a comet with the unaided eye, so do not miss out!

To the right of the W-shape, is the Andromeda Galaxy. It is the most distant object that can be seen with the unaided eye, a staggering 2.25 million light-years away! The hundred thousand million stars that make up the Andromeda galaxy are what allow us to see it over such a vast distance.

Looking to the east, you can see Orion rising from 9pm, meaning that winter is here!

In the chart to the left (click it for a larger map), Mirphak (with Comet Holmes passing by) is visible at the top-right, in the constellation of Perseus. In the constellation of Auriga to the bottom left is the bright star Capella. Below Perseus is Taurus, with the beautiful desert-island cluster of stars called the Pleiades. Also known as the seven sisters (because seven stars are just about visible to the unaided eye), the Pleiades are about the same size in the sky as the full Moon. In fact, the Moon is not too far away from the Pleiades on 23rd and 24th of November.

The planet Mars, the only planet that is sociable this month, can be seen to the left of Taurus, in the group of stars that form the constellation of Gemini.

And finally, we have the beautiful Orion. The red supergiant star to the top left is Betelgeuse, and to the bottom right is the white hot star Rigel. In the middle of both is Orion's belt of three bright stars. Hanging down from the belt is a dagger of three fainter stars, at the centre of which is Orion's nebulae – a cloud of gas and dust where new stars are forming.

The Orion nebula is easily visible to the unaided eye, and is a splendid sight to see even in a small telescope throughout the winter.

Comet Holmes has dramatically increased in size over the last few weeks - it is now even bigger than the Moon in the night sky! However, it has also faded significantly - it is now a challenge to see from light-polluted London, but it is still easily visible from anywhere remotely dark. The photograph to the right was taken by planetarium presenter Tony Sizer on the night of 15 November 2007.

A spectacular sequence of images, taken by John Pane, shows exactly how Comet Holmes has changed over the last month.

What we believe happened is that the surface of the comet somehow ruptured, exposing fresh ice to the heat of the Sun. This ice then vapourises into a halo around the comet, similar to clouds in the sky on Earth. As we all know, clouds in the sky reflect sunlight, which is exactly what the cloud around this comet is doing. As the cloud increases in size, it appears brighter.

In Tony's picture, you can actually see stars through the cloud of water surrounding the nucleus of the comet.

More details about the comet can be found in the Wikipedia entry.

If you you want to observe Comet Holmes yourself, look for a fuzzy object very close to the bright star Mirphak in Perseus. This map (click on it for a larger version) will help guide your eye towards Mirphak, high in the east in the evening - just look down from the easy-to-spot "W" of stars that form the constellation Cassiopeia.

We have very long nights in the northern hemisphere during December – perfect for astronomy!

Here in Greenwich, the sun is setting at 4pm in the afternoon and not rising again until 8am – giving 16 hours when the Sun is below our horizon.

When you take evening and morning twilight into account, we have 14 hours of beautiful star-filled darkness... if you can get far enough away from light pollution.

The long nights are due to the Earth being tilted by 23.5°. In December, the northern hemisphere of the Earth is pointing away from the Sun, so the Sun appears much lower in the sky, and its warmth is diminished. On 3 January 2008 the Earth is actually 3.4% closer to the Sun than in June – but it certainly doesn't feel like that here in the Northern hemisphere!

In the early evening around 6pm, we look westwards to see the patch of sky that used to be directly above us in winter. So, ironically, the Summer Triangle is visible throughout winter! In fact, from the UK, Deneb is a circumpolar star – meaning that it never sets below the horizon.

During December, we have four hours after sunset to see the Triangle before it follows the Sun below the horizon. By February however, you will only be able to see the Triangle in the early morning sky, just before sunrise. Look at my earlier posting to read about the interesting objects in the Summer Triangle.

Look towards the west this month at 8pm, and you are looking towards the centre of our galaxy, where a super-massive black hole lurks just below the horizon. You need to wait until the summer for a better view of that patch of sky, as we are on the opposite side of the Sun to the galactic centre and so the Sun hides it from view.

Rotate 180° to look east, and you are looking directly out into deep space, towards the constellation of Orion.

At the bottom of Orion, to the left of Rigel, is the Orion nebula – a cloud of gas and dust, collapsing to form the latest generation of stars, recycling materials from old, now dead, stars. And you can see that for yourself with binoculars.

Mars is also visible towards the east at 8pm, in the constellation of Gemini. Mars appears to the unaided eye as a bright red object, but you will need an expensive telescope to see any details on the surface of the planet.

And finally, Saturn is becoming sociable again! It is rising in the east at 11pm in the constellation of Leo, where you can find it just to the left of Regulus. It is cream coloured and quite bright – take a look through binoculars, and you may be able to see the rings of Saturn, which show up easily in even the smallest of telescopes.

Here's to dark and clear skies in December!

Comet Holmes now appears almost twice the diameter of the full Moon in the night sky.

To see the latest images, see the gallery at Spaceweather.com.

Because the comet is so large in the sky, it is spread out, making it appear much fainter in the night sky. But it is still visible to the unaided eye when well away from light pollution.

The best way to observe the comet now is with a pair of binoculars that are large (to collect a lot of light) but with low magnification (because the comet is so large in the sky).

The apparent size and brightness of Comet Holmes is regularly estimated by amateur astronomers world wide. A list of estimates is available at the IAC/ICQ/MPC website. Using averages of these estimates, I have plotted the apparent size of Comet Holmes against time (below).

In this graph, you can see the number of days along the bottom since 24 October, 2007 - the date when Comet Holmes suddenly increased in brightness.

Up the left hand side of the graph, I show the angular size of the comet - that is how big the comet appears to us in the night-time sky. The apparent size of the Full Moon, which is half a degree across (or 32 arc-minutes) is labelled for comparison.

Up the right hand side of the graph, I show the actual size of Comet Holmes in millions of km (assuming that the comet is at a fixed distance of 1.7 AU away - although the comet is moving away from us, it has not moved too much over the last 2 months).

Note how within days of the outburst in October, the comet was bigger than the separation of the Earth and the Moon, and within weeks it was physically bigger than the Sun!

Currently, it appears about 1 degree (60 arc-mins) across in the night sky - that's twice the diameter of the full Moon. In physical size, the nucleus of the comet is now surrounded by a cloud of gaseous water that is over 2.5 times larger than the Sun.

What an amazing comet!

On the night of the 13 December, and the morning of the 14 December, the Geminid shooting star shower reaches its peak.

The Earth will be ploughing through a stream of debris left behind by asteroid Phaethon, and we see these fragments burn up as they hit the Earth's atmosphere, causing the shooting stars.

And they are often big fragments! I myself saw a huge fireball in the UK during the Geminid shower of 1994.

More details can be found at the NASA science website.

Details of all the major annual meteor showers visible from the UK are available on the NMM website.

Happy solstice to all our readers!

The winter solstice this year occurs at 6am, on 22 December, 2007.

That is the time when the Earth's North pole is pointing directly away from the Sun (which is why it is so much colder in the Northern hemisphere).

For people living in the Southern hemisphere, the South pole is pointing towards the Sun, making it summertime 'down-under'!

On New Year's day, Comet Tuttle will be closest to the Earth, a mere 25 million miles away, and also at its brightest. The comet will just be visible to the unaided eye, so you will need to be observing from a very dark site.

A gallery of images, and sky maps of when and where to look, can be found at SpaceWeather.com.

[Image of Comet Tuttle taken by Pete Lawrence]

The main highlights for this month are Orion, Mars and Saturn.

There is lots to see in Orion, which is visible around the South throughout the evening (click on the map to the left for a bigger version).

Betelgeuse (a name that is often thought to translate from 'armpit of the central one'!) is a red supergiant star, to the top left of Orion. It is so big that if the Sun were to be replaced by Betelgeuse, the outer layers of the star would lie in the asteroid belt between Mars and Jupiter. The outer layers of the star also have the density of air.

To the bottom right is Rigel, a white supergiant star about 40,000 times brighter than the Sun.

Between the two are the three belt stars of Orion. The far left star in the belt is Alnitak, and close to that star is the Horsehead nebula, unfortunately too faint to be seen with the unaided eye (nebula is a Latin word meaning cloud).

One nebula that is visible to the unaided eye is in the dagger stars that hang down from the three belt stars. Take a look through binoculars and - wow - what a sight! Even better through a small telescope. I will talk more about the Orion nebula in a follow-up posting soon.

To the top right of Orion is the constellation of Taurus, the Bull, with the bright red giant star Aldebaran forming the eye of the bull. To the top right of Aldebaran are the Pleiades - a beautiful cluster of stars that is a delight in binoculars. Don't bother looking at the Pleiades through a telescope however, unless you have a very wide angled lens, since this star cluster is far too big, being bigger than the Moon!

But what about the planets?

Well, the five main planets have all been known about since antiquity, thanks to them being so blindingly bright. Mars is especially so at the moment, due to it being on the opposite side of the Earth to the Sun. It is around the south all night - just look for the brightest red object you can find in the sky!

After admiring Mars, and if it is later than 8pm, look to your left by 90 degrees to see another bright planet, Saturn. How do you know if you've found it? Well, take a look in binoculars, and you may just be able to see the rings around Saturn - although you will need a small telescope if your eyes are older than 30.

To the top right of Saturn is the bright star Regulus, and above Saturn is the bright star Algieba - a beautiful orange-yellow double star system, well worth a look with a telescope while looking for Saturn's rings.

The Orion Nebula is a wonderful sight, in binoculars or a telescope - but it is often difficult to compare what you see with your own eyes through a telescope with photographs of the same region. Hopefully, the changing image beneath will help you compare the two views of Orion with ease!

That is because the human eye is not very sensitive, equivalent to just a few seconds of a photographic exposure. So when you look with your own eye through a telescope, you only see the brightest part of the gas cloud, at the very heart of the nebula. But long-exposure photographs pick up even the faintest details.

The two photographs above, taken by Martin Morgan-Taylor (assisted by his two cats and myself), show both these extremes. The short exposure photograph was only a 30 second exposure, and this is similar to the view that amateur astronomers witness when looking down the eyepiece of their telescope. The longer exposure is 900 seconds long, showing much more detail in the nebula than can be seen with the eye.

The 27-metre diameter asteroid 2008 AF3 will tonight pass by the Earth as close as the Moon (see its orbit here).

In fact, it is passing so close that you can see it for yourself (from a dark site, with a large telescope). At magnitude 14, you will need a 12" diameter telescope to spot it as it passes through Ursa Major (the Plough) this evening (you can plot its position from your locations using Tom's Asteroid Flybys Webpage).

But the worry is that it was only discovered 3 days ago, highlighting the difficulty of finding asteroids that are coming straight for us!

If an asteroid is larger than 100m, and is expected to pass the Earth within 20 times the Earth-Moon separation, then it is considered a potentially hazardous asteroid. Fortunately, none are expected to hit the Earth at the moment, but new ones are being discovered on a regular basis.

According to SpaceWeather.com there are currently 917 potentially hazardous asteroids out there. A full list is maintained by the Centre for Astrophysics at Harvard.

The two comets are Comet Holmes and Comet Tuttle - both visible to the unaided eye at the moment, if you manage to get away from all those inefficient city lights. If not, binoculars will help you spot the pair.

Comet Holmes, still visible to the unaided eye from a dark site, is still getting bigger - it is now three times the size of the full moon! The image to the left was taken by Toni Scarmato in Italy, with the comet approaching the bright star Algol. It will get closest to Algol on 22 January, so that will be a great time to take a look.

Because it is so big, you do not need any specialist equipment - just a digital camera with lens will do. For lots of examples, see the SpaceWeather.com gallery. It is visible high in the sky, in the constellation of Perseus - halfway between Cassiopeia and the face of Taurus the bull.

But the big question that everyone is asking is - will Comet Holmes outburst again? When it was first discovered in 1892, it faded for about 70 days until it suddenly brightened again. Will history repeat itself? If so, the comet may brighten again any time now. (The full history of the discovery behaviour of Comet Holmes can be found at Gary Kronk's Cometography website.)

While Comet Holmes is very high in the sky from Greenwich, Comet Tuttle is much lower, just 25° above the horizon in the constellation of Cetus the Whale (or sea monster), well below Perseus. Images and maps of Comet Tuttle can be seen on the SpaceWeather.com website.

The nights of 24-25 January are a great time to see the planet Mercury.

The best time to look is within 10 minutes of 17:10 local time. Any earlier, and the bright glow of the Sun gets in the way; any later, and Mercury will be too low in the sky. At this time, Mercury will be 9 degrees above the horizon - about the size of your outstretched hand at arm's length above the horizon. You can find it in the south-west. It is visible to the unaided eye, but it can be a difficult planet to spot.

But, by the 30^th of January, Mercury has disappeared, hidden in the glare of the Sun once again.

The reason why Mercury is so difficult to see (can you spot it in the photograph to the left?) is that it is the closest planet to the Sun, and so when we look in the night sky, Mercury is always pretty close to the Sun. But every 3 months there are a brief few days when Mercury gets to the extreme of its orbit, as viewed from the Earth.

Note to the expert amateur astronomers: the highest altitude of Mercury after sunset is different to the day when Mercury is at its maximum eastern elongation. So even though Mercury got to its most easterly point in its orbit on 22 January, it gets slightly higher in the sky at sunset for the following few days.

The next time Mercury is around the evening sky is in mid May, when it will be 4 degrees higher in the sky at sunset, making it slightly easier to spot.

Mercury is also in the news thanks to the NASA Messenger probe. On 14 January, Messenger took some great pictures of Mercury during a close fly-by.

If you are an early riser, look South-East at 6:30 AM local time - and there you will see the planets Venus and Jupiter very close together in the morning twilight!

Venus is the brighter of the two planets, and is heading closer and closer to the Sun every day.

The planet Mars is visible throughout the night this month – just look south for the brightest reddest object, high in the sky. Mars is visible from sunset until it heads towards the low western horizon at 1am.

On the evening of 15 February, the Moon is close to Mars, making it even easier to spot. But this meeting of the Moon and Mars only lasts a night, before the Moon continues on its monthly journey around the night sky.

The map to the left can help you find Mars by matching up the surrounding stars – the map shows you exactly what you will see when you look towards the south, before 10pm (after which, you have to start rotating the map significantly clockwise).

Mars is currently in the constellation of Taurus, and so is the red giant star, Aldebaran. Also in Taurus, is the Pleiades star cluster – a beautiful sight! Literally hundreds of stars are visible in binoculars. It often reminds me of a little desert-island of stars hidden in a vast sea of inky black space. It is the little cluster of stars at the far right of the map above.

The ringed planet Saturn is rising at 7pm in the East, close to the star Regulus in the constellation of Leo. As we look up to the night sky on the 20th, the Moon is very close to Regulus. Just to the East of the pair (that is, just to the left for northern hemisphere observers) you will find Saturn. Even a small telescope shows up the remarkable rings that surround the planet. Even though the rings of Saturn look solid through a telescope, they are made up of literally billions of fragments of rocks – some the size of dust, and the biggest ones the size of a small car.

Remember, the planets Mercury, Venus, Mars, Jupiter and Saturn all reflect so much light from the Sun that you can easily see them with your own eyes, albeit at various times of the year. That is why we've known about these planets for maybe 10,000 years or more. You've just missed out on seeing Mercury (it is next visible in the evening sky in May), but Jupiter and Venus can both be seen as the two bright points of light in the early morning sky – look east in the very early morning twilight.

And, finally, Orion is still prominent, with its nebula easily visible with your own eyes. As you look at the nebula though binoculars, even from the light pollution of London, you can see it is very different to the pin points of stars that surround it. Take a look through a telescope, and you get an even more impressive sight!

Two eclipses will be visible this month.

First, we have an annular solar eclipse occurring on 7 February 2008, visible in Antarctica and the very southern Pacific Ocean.

An annular eclipse occurs when the Sun and Moon perfectly align, but the Moon appears smaller than the Sun in the sky, leaving a ring of sunlight visible around the Moon. This is due to the Moon being slightly further away than usual in its elliptical orbit. If you have never seen an annular eclipse, click on the image to the left to see the time-lapse movie (in Windows Media Video format) of the 2005 annular eclipse, as visible from Madrid.

The eclipse is also visible in south-eastern Australia and New Zealand, as a partial solar eclipse. (A partial eclipse occurs when the Sun and Moon do not perfectly align.) In New Zealand, up to 65% of the Sun will be covered by the Moon.

A fortnight later, on 21 February, a lunar eclipse occurs on the opposite side of the sky (and so is visible on the opposite side of the Earth), once the Moon has moved around to the other side of the Earth - from being in-between the Earth and Sun, to being in the Earth's shadow. This lunar eclipse will be visible from Western Europe (including the UK), Western Africa, all of South America, and central and Eastern parts of both the USA and Canada. This lunar eclipse lasts from 00:30 until 6:20 GMT – basically, throughout the night!

Click on the image for a time-lapse movie (format: Windows Media Player)

Full details of both eclipses can be found at the NASA eclipse website.

But why do eclipses usually occur in pairs?

The Moon's orbit around the Earth is tilted by 5 degrees compared to the flat plane of the rest of our solar system. So the Moon is literally going above and then below the solar system. An eclipse can only happen when the Moon is moving up or down across the flat solar system, passing in front of the Sun – in astronomy terms, an eclipse can only happen when its nodal axis (see figure) is aligned with the Sun.

That is what will happen in February, and again about 6 months later, when the Earth has moved to the other side of the Sun, in August 2008.

If the Moon happens to pass through the Sun-side nodal axis (point 2) within 5 days of them aligning, then you get a total (or annular) eclipse of the Sun. If the Moon passes through this point within 15 days of the alignment, you will get a partial solar eclipse instead.

On the other side of the Earth, if the Moon passes through the shadow of the Earth (point 1), a lunar eclipse will occur. And you have about 10 days grace in which to do that, around the time that the nodal axis points at the Sun.

With all this leeway for getting an eclipse around the time the nodal axis points at the Sun, it is technically possible to get 3 eclipses in one month! This last occurred in July 2000, when there was a partial solar eclipse near Antarctica, then the Moon raced around to enter the heart of the Earth's shadow a fortnight later, and the month finished with another partial solar eclipse visible from near the Arctic.

Here is a beautiful photograph of the 7 February solar eclipse, as seen from New Zealand. The photograph was taken by Andy Dodson and Deborah Hambly in New Zealand, where, as described in an earlier post, the Moon covered 59% of the Sun.

The photograph shows lots of activity around the limb of the Sun. These prominences are jets of hot gas, propelled outwards along the magnetic field lines of the Sun. Click on the image for a larger version.

The Space Shuttle Atlantis successfully docked with the International Space Station today - and you can see them fly overhead for yourself. The pair are astonishingly bright - all you need to do to see them is to look up at the right time!

You can see the space station rising in the West, flying over the South, before heading towards the East. It crosses the entire night sky in about 5 minutes. Remember - if it flashes, it's an aircraft, but if it has a constant brightness, then you are looking at a satellite. To confirm that you have seen a satellite, keep watching to see if it suddenly disappears into the shadow of the Earth.

The following table gives the (approximate) times (within 1-2 minutes) when the International Space Station is flying over the UK for the next week.

10 Feb, 18:34-18:38 GMT, peak 74° high
11 Feb, 17:20-17:25 GMT, peak 85° high
11 Feb, 18:55-18:58 GMT, peak 44° high
12 Feb, 17:40-17:46 GMT, peak 78° high
12 Feb, 19:15-19:18 GMT, peak 23° high
13 Feb, 18:01-18:06 GMT, peak 48° high
14 Feb, 18:21-18:26 GMT, peak 25° high
16 Feb, 17:27-17:32 GMT, peak 28° high

If you live outside the UK, see Heavens-above.com for times when the space station can be seen flying over your location.

Most sky-watchers will recognise the familiar sight of Orion, the constellation which is dominating our view of the night sky at the moment.

But how would Orion look if we had X-ray eyes?

Objects at different temperatures give off light at different wavelengths. We can see this on the thermometer below. People are far too cold to give off visible light - we emit infrared light instead. Unfortunately, our eyes are not sensitive to infrared light, which is why we cannot see each other in the dark.

We humans rely on light originating from objects at a temperature of 2,000-12,000°C - objects that emit visible light. At 5,500°C, the Sun gives off plenty of visible light, as does a light bulb containing a filament glowing at up to 3,000°C.

But there are some things in our Universe that are much, much hotter... at millions of degrees Celsius.

From stars falling into black-holes, to neutrons stars speeding through space at 300,000 miles per hour; from supernovae explosions colliding with interstellar gas, to white dwarf stars being bombarded with a thousand million tonnes of gas… every second.

All of these (and more) emit X-ray radiation.

The slideshow below cycles through the familiar visible view of Orion, to the unfamiliar X-ray view of Orion.

The X-ray view of Orion was put together by Konrad Dennerl & Wolfgang Voges at MPE in 1995, to celebrate 5 years of ROSAT. Rosat was a German/US/UK X-ray space-telescope, that operated from 1990-1999.

When comparing the two views of Orion, pay particular attention to:

• Orion’s belt, the Orion nebula, and Sirius - all of which are emitting both X-ray and visible light.
  
• The Crab nebula, which is very faint visually, but is very X-ray bright.
  
• The Moon and Betelgeuse - both are visibly bright, but X-ray faint.
  
• The star Sirius, which is a double star system, made up of the stars Sirius A and Sirius B. Sirius A is 10,000 times brighter than Sirius B to our own eyes, and so the visible image is dominated by light from Sirius A. However, Sirius B is a hot white dwarf star which emits lots of X-rays, and so the X-ray image is dominated by the light from Sirius B.
  

So the next time you gaze upon Orion, think how different it looks through X-ray eyes.

In the early hours of the morning of Thursday 21 February (the night of Wednesday 20 February) there will be a total lunar eclipse. The event will be visible from Western Europe (including the UK), Western Africa, all of South America, and central and Eastern parts of both the USA and Canada.

The times for the event are as follows:

• 00:30 GMT: The Moon begins to enter the Earth's penumbral shadow at 00:30 GMT - you may not even notice this, since the Moon will only be slightly darker
  
• 01:43 GMT: The Moon begins to enter the Earth's umbral shadow - this is when the full Moon begins to get really dark!
  
• 03:01-03:51 GMT: The entire Moon is now in the dark umbral shadow of the Earth, although some red sunlight will get through the Earth's atmosphere and illuminate the Moon, giving it a deep red colour
  
• 03:51 GMT: The Moon begins to leave the umbra and enters the other side of the penumbra
  
• 05:09 GMT: The Moon has left the umbra behind, and is almost fully illuminated by the Sun again
  
• 06:20 GMT: Moon leaves penumbral shadow
  

But what are the penumbra and umbra shadows? Well, take a look at my tea mug to the left. As you can see, when I cast a shadow of the mug onto the desk using a lamp, there are two shadows - a lighter penumbra shadow, and a much darker umbra shadow. These two shadows are caused by the width of the light bulb (or Sun). If the light source was a tiny pin-point of light, there would only be one deep shadow.

As a taster, below is a time-lapse movie of a total lunar eclipse that occurred in 2006.

Click on the image for a time-lapse movie (format: Windows Media Player)

If, like me, you were clouded out last night, you can enjoy the lunar eclipse through the SpaceWeather.com gallery. The image to the left was taken last night by Mohammad Taher Pilevar, in Hamedan, Iran.

Eclipse totale de lune, 21 février 2008 /Total lunar eclipse, February 21 2008
Originally uploaded by Laurence_

Last night's eclipse has triggered a spate of activity on Flickr – total lunar eclipse was the most popular tag in the last 24 hours. We have picked out a few shots and saved them in our favourite photos, including the nice shot of the Moon against clouds above.

If you are interested in learning more about astrophotography, we are running a photography workshop on 4th March. Tickets are £15/£11 and must be booked in advance.

The mighty constellation of Orion is still dominating the evening sky. But by May, the Earth will have moved so far around the Sun that Orion will be hidden behind the Sun's glare. So admire Orion while you still can!

The same can be said for Mars, too. Mars is leaving Taurus, and moving into the constellation of Gemini. And Mars is fading rapidly. During December, Mars was blindingly bright, because we were so close. In the orbital race around the Sun, the Earth took the inside line and has now left Mars behind. In March, Mars will be twice as far away from the Earth as it was in December... and so Mars appears 5 times fainter than it did.

On the evening of the 12th, the Moon will glide past the Pleiades open cluster, as it does quite regularly. Because the Moon is so bright, it is often difficult to see any of the Pleiades stars at that time. In my photograph on the right, the Pleiades were so faint compared to the Moon that I have had to overlay an older image of the Pleiades on top.

On the morning of the 15 March, at 3am, the Moon and Mars will be very close together. It must be worth getting up early to look for an interesting foreground object, to take a unique photograph of the pair so close together?

On the evening of the 18th, there is the beautiful trio of Saturn to the left, Regulus in the middle, and the Moon just to the right, high in the evening sky, all in the constellation of Leo. If you have never seen how quickly the Moon races around our planet, take a look on the night of the 18th, and then again on the following night to see just how much the moon has moved in relation to Saturn and Regulus.

In fact, Saturn is the best planet to see throughout the month. Just look south in the evening sky to see Saturn on the left, and Regulus on the right. Saturn does look slightly yellow to the unaided eye. Any small telescope will reveal those amazing rings!

This year, the equinox is on the 21st, at 05:48am. In winter, the Earth is tilted directly away from the Sun, and in summer, the Earth is tilting directly towards the Sun. But at the equinox, the Earth is pointing at a right-angle from the Sun, pointing neither towards nor away from the Sun. On this day, the length of both the day and night are equal – hence the name, equinox.

Why not print off your own skymap for the month, or try out the free Stellarium planetarium software.

The Moon has reached first quarter in its moonthly orbit around the Earth (a small mis-spelling of the word month, and you realise where the word originates from!). You have about 6 hours to admire the moon after sunset, until it too sinks below the western horizon, due to the relentless rotation of the Earth.

Most of us are used to the familiar sight of the first-quarter Moon through our own eyes. But the sight through an X-ray telescope is perplexing, to say the least.

As described in my previous post, X-rays originate from very hot gas. In the case of the Moon, the X-rays originate from hot gas bursting out of the Sun, which are then reflected off the Moon.

In 1990, the Rosat observatory took this image of the Moon.

It is somewhat ironic that X-ray astronomy began in the early 1960s, with the aim of detecting X-rays from the Moon. The plan was to get some clues about the conditions on the lunar surface before Neil and Buzz got there before the decade was out.

But it took another 30 years to detect those X-rays from the Moon!

Even more ironically, it turned out that the Moon wasn't the really interesting bit after all. Look at the X-ray dark half of the Moon, and you notice that it is actually darker than the deep space behind it...

And that raises the question – where are all those X-rays behind the Moon coming from? (The dark side of the Moon is not completely black, as some charged particles from the Sun do collide with the far side of the Moon, producing X-rays.)

To know what was causing the X-ray background, we had to wait for Chandra, which showed that at least 80% of the X-rays originated from distant star-swallowing black holes – half of which are about the mass of the Sun, the other half being a billion times larger! (see here)

The image taken by Chandra is both boring and astounding at the same time! Boring, since the image is just a collection of dots. Astounding when you realise just what those dots actually are.

So how many black holes does the full Moon cover?

Well, it depends how sensitive your X-ray telescope is and for how long you look! But there will be anything between 100 and 1000, depending on where you look in the sky (it is easier to see black holes looking directly out of our galaxy).

Spring is here, so it is time to say goodbye to Orion until next winter! By the end of April, it will by hidden by the glare of the Sun, and during June the Sun will be directly above Orion.

The Sun is setting later and later, setting now at 8pm summer time. In fact, the Sun is setting 40 minutes later at the end of the month than at the start. Although the nights are getting shorter, making it more difficult for observing, it is also getting warmer - a welcome relief to anyone who has been observing in sub-zero temperatures this winter!

The Moon is a wonderful sight in the evening for the first few weeks of April, but the full Moon is on the 20th, making it very difficult to see any but the brightest stars. Last quarter is on the 28th of April, so that is another good opportunaty to observe the fainter objects this month.

The only planets visible in the evening this month are Mars (look west for a red object all evening, although it gets very low in the sky after midnight), and Saturn (high in the south at sunset, and setting in the west at 3am).

Saturn is easy to spot this month since it is so close to the bright star Regulus, in the constellation of Leo (Saturn is the slightly fainter of the two). On the night of the 14th of April, the Moon is just to the right of the pair, and on the following night, the Moon is just below the pair.

If you have never seen the rings of Saturn before, then those two nights are the best time to be amazed by the sight, with the Moon acting as a very helpful guide, and Saturn being at its highest point in the sky at sunset in the evening - very convenient!

We know summer is rapidly approaching, because the summer triangle is once again visible in the evening sky, rising during April at around 10pm.

And for those staying up really late, Jupiter is very bright indeed. Just look towards the south-east to see Jupiter rising at 3am. If you have binoculars, take a closer look and you may be able to see up to 4 moons orbiting around Jupiter.

To see a satellite from the ground, you need them to fly over at just the right time - either dawn or dusk. In daytime, the sky is too bright to see them. At night, the satellites are in the shadow of the Earth an so cannot be seen.

The next six weeks are the perfect time to see the space station flying over head.

The amazing image to the left were taken by Dirk Ewers of Hofgeismar, Germany, using just a 5 inch refracting telescope!

If you want to see the space station fly overhead, all you need to know is when and where to look - which the very easy-to-use SpaceWeather.com satellite tracker will tell you.

The International Space Station can get extremely bright. Don't forget - If you see something passing over head with a flashing light, then it is a aircraft! If it has a constant brightness, it is a satellite. Also, satellites disappear suddenly as they enter the shadow of the Earth.

The long days of summer are here again, allowing us to make the most of a full day in the Sun. In June, the Sun is rising over the UK at 04:45 BST in the morning, and setting around 21:20 BST in the evening, giving us almost 17 hours of continuous daylight.

The summer solstice occurs on the 21st of June. That is the day that the Earth's northern hemisphere points in the direction of the Sun, making the Sun high in the sky at noon. At midnight, the Sun is only 15 degrees below the horizon, not enough for it to get astronomically dark.

The word planet originates from the Greek meaning 'wanderer'. As the planets orbit around the Sun, they slowly wander across the starry background. During June, Mars and Saturn are both wandering closer towards each other in the night sky - look west for the pair before they set at 11pm. On the 7th of June, the Moon is conveniently next to Mars, and a day later, Saturn, the bright star Regulus and the Moon are all conveniently close together.

At the end of the month, the bright planet Jupiter can be seen rising by 10pm at the end of the month. Take a look through binoculars, and you may be able to spot its four bright moons - just as Galileo first did almost 400 years ago.

The word planetes is Greek in origin, meaning 'wanderer'. As the planets orbit around the Sun, they move slowly across the starry sky. This month, Jupiter wanders into a very good position, being very bright and visible throughout the evening in the south. Saturn and Venus are also visible for the first half of the month - look towards the west just after sunset.

Let's look at these 3 planets in more detail.

The very bright planet Jupiter is rising in the east just before the sun sets throughout July, and is prominent until after midnight. Looking at Jupiter through binoculars, you can see up to four moons that orbit the planet. These are collectively called the Galilean Moons after the man who discovered them through the first astronomical telescope 400 years ago.

At the start of the month, Venus and Saturn are visible to the west after sunset. The pair are close to each other all month, with Saturn just to the right of Venus. They are visible until 22:30, after which they follow the Sun and set in the west. By the end of the month, both Venus and Saturn are hidden by the glare of the Sun. Because Venus orbits the Sun quicker than the Earth does, it will move in front of the Sun during July until, on the 18th of August, Venus lies between the Earth and Sun. Saturn takes 29.4 years to orbit the Sun, and so it is the relatively rapid motion of the Earth that causes Saturn to be hidden behind the glare of the Sun.

At this time of year, the Earth is on the side of the Sun which allows us to see constellations such as Hercules, Cygnus and Lyra.

In Cygnus, the star that makes up the head of the swan is called Alberio. Although it looks like a lone star to the unaided eye, looking at the star through a small telescope or binoculars reveals that this is actually a double star. It is the stark difference in colours that makes this double star such a delight. Although there has been no sign of any orbital motion of the last hundred years of observation, calculations suggest that they orbit around each other once every around 69,500 years!

Close to Alberio, in the adjoining constellation of Vulpecula the fox, is the Dumbbell nebula. It is visible with a small telescope, some 1,300 light-years away. In the centre of the Dumbbell is a faint white dwarf star, the left over core of the star that puffed out its outer layers to form the nebula. From observing the speed of expansion, the nebula is estimated to be about 11,000 years old.

In Lyra, another nebulae is visible through a small telescope - the ring nebula. Looking like a ring of smoke, it can be easily found between beta & gamma Lyra 1500 light years away. At the centre is faint but very hot blue dwarf star, which is emitting intense UV radiation which causes the ring to glow. The inner edge of the gas is green due to the illuminated Oxygen, and the outer edge is red due to illuminated Hydrogen and Nitrogen. The gas is in the shape of a rugby ball around the white dwarf, half a light year across.

Visible towards the North-West this month is the great globular cluster in the constellation Hercules. From a dark site the cluster is just visible to people with sharp eyesight, but through a telescope the sight is stunning. It contains about one million stars! The cluster is about 24,000 light-years away and some 160 light-years across, with an age of about 10 thousand million years.

The neighbouring constellation to Hercules is Bootes, containing the bright red-giant star Arcturus. Arcturus is 16 times wider than our own Sun, and over 100 times brighter. The handle of the Plough points towards Arcturus and on towards another giant star called Spica. This can be remembered by the ditty "Follow the arc to Arcturus, and speed on to Spica!".

Spica is in the constellation of Virgo, which also contains the Virgo group of over 1000 galaxies. Many of the brighter galaxies are visible in small telescopes, including M87, the 87th member of Charles Messier's catalogue of interesting astronomical objects.

On Friday the 1st of August, there will be a total eclipse of the Sun. The total eclipse will be visible from a narrow path crossing the Earth, starting in Northern Canada, passing over Greenland & the Arctic, and then into Russia, Mongolia and China.

The eclipse will occur between about 8am and 1pm GMT, but the exact time depends on where you are on the planet. In the UK, the eclipse will be partial and will last between 9:30 BST and 11:20 BST.

However, from London at most only 20% of the Moon will cover the Sun (as in the image to the left); from Scotland, the Moon will cover up to 40% of the Sun.

The Royal Observatory, Greenwich will be opening at 09:15 in order to catch the start of the eclipse, and with support of the Flamsteed Astronomical Society, the public will have the opportunity to view the eclipse through solar telescopes.

Full details of the eclipse can be found at the NASA eclipse website, or at SpaceWeather.com.

Remember, NEVER look directly at the Sun! Doing so will burn a hole in your retina, blinding you for life. So always use a solar filter, or project the image of the eclipse Sun onto the ground, using your hands like this to project an image like this, or even a scarf like this to project an image like this... or even use a hat!

Below is a time-lapse of the 2005 total solar eclipse, as seen from Egypt.

The highlight this month is Jupiter, rising in the South-East at sunset before commuting towards the South-West overnight. Take a look through binoculars and you will be able to see up to four moons around the planet. Take another look just a few hours later, and you may notice that the moons have moved slightly in their orbit around Jupiter.

Every August, the Earth ploughs through dust and debris left behind by comet Swift-Tuttle - and this produces the Perseid meteor shower. It's a bit like driving a car through snow fall, where the car is planet Earth, and the snow flakes are the bits of cometry dust, that burn brightly and briefly when they hit the atmosphere.

It's called the Perseid shower because, during August, the Earth is moving towards the constellation Perseus as it orbits around the Sun at 70,000mph. So lots of meteors appear to be coming from that direction!

At this time of year, the Earth is on the side of the Sun which allows us to see constellations such as Hercules, Cygnus and Lyra. We are also on the side of the Sun that is nearer to the centre of our galaxy - so we get a great view of the Milky-way arching over head this time of year. But you will have to go somewhere dark to see it at its best, well away from any inefficient lighting.

In Cygnus, the star that makes up the head of the swan is called Alberio. Although it looks like a lone star to the unaided eye, a small telescope or binoculars reveals that this is actually a double star. It is the stark difference in colours that makes this double star such a delight. Although there has been no sign of any orbital motion of the last hundred years of observation, calculations suggest that they orbit around each other once every around 70,000 years! The pair are visible with a small telescope, so take a look.

The next week is the best time of the year to go looking for shooting stars (also called meteors). A shooting star is not actually a star at all, but a bit of dust. As that dust hits the Earth's atmosphere, it burns brightly for just a fleeting moment, and we see it as a streak of light across the night-sky.

Next week is the best time of the year to look because the Earth just so happens to be going through the part of the solar-system that Comet Swift-Tuttle went through back in December, 1992. And that comet left lots of dust behind.

The Earth drives through this dust like a car driving through falling snow. So we get the best view of the meteors when we are on the 'front' of the Earth - that's in the early morning. So the best time to see meteors this year is early morning on the Tuesday 12 August, when the Earth is at the heart of the stream of dust. Make sure you wait for the Moon to set as well, and get as far away from light pollution as possible - such light can drown out the view of all but the brightest meteors.

Comet Swift-Tuttle's tail was quite wide, so we should see a larger number of meteors than usual for the next week. Click here to see the orbit of Comet Swift-Tuttle around our solar system.

On Saturday the 16^th of August, we get to enjoy a lunar eclipse! A lunar eclipse occurs when the Moon goes into the shadow of the Earth.

It is no coincidence that we have a solar eclipse (when the Moon casts a shadow onto the Earth) and a lunar eclipse (when the Earth casts a shadow onto the Moon) just a fortnight apart...

Because the orbit of the Moon is tilted, it travels from the South of our flat solar-system to the North, and back South again every month. During the eclipse on the 1st of August, the Moon was travelling from the North down to the South... and as it did so it happened to pass in front of the Sun. On the 16th of August, the Moon is heading North again, passing though the shadow of the Earth on its way.

It is also no coincidence that we are having a pair of eclipse's six months after the last pair! This is because the nodal axis of the lunar orbit happens to be in line with the Sun at the moment, which happens every six months because the Earth orbits the sun every year (see the graphic to the left, and my earlier post from the February eclipse season for more details).

This lunar eclipse will be visible from everywhere with the exception of the continent of North and central America (see this map). The animation I have created below using the excellent (and free!) Celestia software explains why the eclipse is not visible from the top half of the America's... our planet gets in the way!

But for us here in the UK, the Moon will be rising in eclipse, so we have some tremendous and unique photographic opportunities to look forward to!

And what will the eclipse look like? Well, the Moon will turn either a deep red, a pink colour or maybe grey... we really don't know! Take a look and find out for yourself! It all depends on the atmospheric conditions of the Earth at the time of the eclipse, since some sun-light will bounce through our atmosphere and illuminate the Moon even when it is in the shadow of the Earth.

The Moon will first enter the outer shadow of the Earth at 18:25 GMT (19:25 British Summer Time) - although, you may not even notice. An hour later, at 19:36 GMT (20:36 BST) the Moon begins to go into the dark heart of the Earth shadow, and that's when the eclipse really begins! The Moon is in the middle of the Earth's shadow by 21:10GMT (22:10BST), and has left the dark shadow by 22:44 GMT (23:44 BST). The entire eclipse ends at 23:55 GMT (00:55 BST).

And for those of you too impatient to wait, below is a time-lapse movie of a lunar eclipse I saw back in March 2007! (click for full details).

In September, Jupiter is the most prominent planet in the night sky. Look towards the South just after sunset, and Jupiter is low in the sky. On 9 of September, the Moon can be seen just below Jupiter, acting as a convenient guide.

At this time of year, the Earth is on the side of the Sun which allows us to look up at constellations such as Hercules, Cygnus and Lyra.

In Cygnus, the star that makes up the head of the swan is called Alberio, a colourful double star in a small telescope.

In Lyra, another nebulae is visible through a small telescope - the ring nebula. Looking like a ring of smoke, it lies 1500 light years away. At the centre is a very hot white dwarf star emitting intense ultraviolet radiation, causing the ring to glow.

Directly overhead in the evening is a triangle of bright stars - Vega, Altair & Deneb. They are known as the summer triangle. Even though the trio appear to be of similar brightness to each other, in reality Deneb is much brighter. It is one of the brightest stars we know of, 250,000 times brighter than the Sun. It only looks as bright as Vega & Altair because it is 100 times further away. If it was as close as either, it would be as bright as the Moon!

Visible towards the North-West this month is the great globular cluster in the constellation Hercules. Through even a small telescope the sight is stunning. This cluster contains several hundred thousand stars, and lives on the very outskirts of our own Milky-way galaxy.

Look towards the North, and you can find the pattern of stars called the Plough (the tail and body of the constellation of the Great Bear, Ursa Major). The handle of the Plough points towards Arcturus, which can be remembered by the ditty "Follow the arc to Arcturus!". Arcturus is a bright red-giant star, 16 times wider than our own Sun, and over 100 times brighter.

The International Space Station is once again visible flying over the UK at dusk.

To see the International Space Station, it needs to fly overhead at either dawn or dusk. Any later in the night, and the station is completely in shadow. Any earlier in the day, and the bright daytime sky makes it difficult to spot.

As the orbit of the International Space Station moves around the Earth, we get windows of opportunaty when we can see the station. We currently have about 10 days when we can see it at dusk, then we have to wait a month for it to be visible at dawn, and then another month until it is visible at dusk again, towards the end of November.

To find out when and were to look, take a look at the SpaceWeather.com flyby prediciton tool, or goto Heavens-above.com.

Oh, and the station is very bright indeed, thanks to it's huge solar panels!

Jupiter is still visible throughout October, setting by 10pm local time. Look low towards the south-west and it is the brightest object in the sky. Take a look through binoculars, and see if you can spot the four bright Galilean moons that orbit around Jupiter. Our Moon is conveniently close to Jupiter in the night sky on the 6th & 7th of October, acting as a useful guide.

The Moon begins the month as a thin crescent - a beautiful sight in the evening sky. The Moon reaches full Moon, when it is on the opposite side of the sky to the Sun, on the 14th.

The summer triangle is still visible in October, despite its name, high in the South at 7pm. The three stars that make up the triangle are Vega, Altair & Deneb. Vega is the brightest of the three stars, and there maybe a planet like Jupiter in orbit around Vega. Altair is interesting because it rotates in just 7 hours! And Deneb is actually one of the brightest stars we know of - some 250,000 times bright than the Sun! The reason it looks fainter than Vega is only because it is much further away - Deneb is some 100 times further away than Vega. If Deneb was as close as Vega, it would be as bright as the Moon!

Throughout November, Venus is becoming easier to see in the evening sky. Look towards the South-West immediately after sunset, and it is very low on the horizon... so low, in fact, that it may be behind any nearby trees! If you cannot spot it, wait until December & January to get a much better view.

Just to the top left of Venus, is Jupiter. Both are very bright and easy to see with only your own eyes. Binoculars will reveal Jupiter's four biggest and brightest Moons.

In the last few days of November, Jupiter and Venus will be very close to each other - just a few degrees apart!

And on the 1st of December, the Moon passes directly in front of Venus! Do make sure you take a look - it is rather strange to see the brightest thing in the night sky suddenly disappear behind the Moon!

Even though the summer has long gone, the Sun is setting so early that we are still able to see the constellations Cygnus, Lyra & Aquila, where the brightest star in each make up the summer triangle. Although these constellations were directly overhead in the summer, they are now low down in the west, ducking beneath the western horizon at 9pm by the end of November - but ideal targets for the early evening.

The star that forms the head of Cygnus the swan is called Albireo, a blue and golden double star that is a beautiful sight with either binoculars or a small telescope. Note that Cygnus is flying directly downwards, head-first into the western horizon! Just to the right of Albireo is the Ring Nebula in Lyra, the left over remains of a star that puffed out its outer layers to form the nebula some 1,500 years ago. And to the left is the Dumbell Nebula, another treat for small telescope owners.

Almost directly overhead, high in the east, is the easily recognisable W-shape of the constellation Cassiopeia. To the right of the W-shape, is the Andromeda Galaxy - it is the most distant object that can be seen with the unaided eye, a staggering 2.25 million light-years away! The hundred thousand million stars that make up the Andromeda galaxy are what helps us see it from such a distance!

Looking to the east, you can see Orion rising from 9pm, meaning that winter is here! Above Orion is Taurus, with a beautiful desert-island cluster of a hundred stars about the same size in the sky as the full Moon, called the Pleiades (or seven sisters as it is also known because seven stars are just about visible to the unaided eye). In fact, the on the night of the 13th, the Moon passes directly in front of the Pleiades.

The Taurid meteor shower is underway, and will last the next few days (until the 12th of November). The shower is caused by the Earth ploughing through debris left behind by Comet Encke.

This year may be a swarm year, but there is only one way to find out for sure... and that is to go outside and look! Since the meteors could appear anywhere in the sky, all you need to do is to look up with your own eyes.

On the evening of the 13^th of November 2008, the Moon will glide across the face of the Pleiades star cluster. This star cluster is also known as the seven sisters, as the seven brightest stars in the cluster are visible to the unaided eye - although over 50 can be seen through binoculars.

We call such events, when one astronomical object covers another, an occultation. So on the 13th, the Moon occults the Pleiades. It begins when the Moon rises in the East at about 16:20 GMT, and it takes the Moon 6 hours to pass across all seven of the sisters.

The event will not look so spectacular, because the Moon's brightness will all but drown-out the view of the star cluster! But take a look through binoculars or a telescope, and you will be able to see the Moon slowly glide over the stars in the cluster over the course of a few hours.

And as it does, just think - You are actually watching the Moon orbit around the Earth, passing in front of the background of stars, at over 2000 mph!

Look low to the South-West just after sunset, and you can see a beautiful pair of planets. But you only have less than an hour and a half to catch this beautiful sight, since Venus rapidly chases the Sun below the horizon.

Over the next few weeks, Venus is getting ever-closer to Jupiter. And on the 1st of December, Jupiter, Venus and the Moon are all within just two degrees of each other... more about that next week!

In the above photograph, Jupiter is to the top-left, and the brighter Venus is to the bottom-right.

Do take a closer look at Jupiter through binoculars or a small telescope - or even a camera! I took the photograph below using just a standard 300mm zoom lens and a Canon 40D camera...

On the 1st of December, the Moon glides in front of the Venus, on its moonthly journey around the Earth.

[Click on the images below for a larger version] Above: The moon begins to hide Venus at 15:50 GMT.

Venus is once again visible at 17:19 GMT.

Jupiter is also visible in the evening sky to the top-right of the Moon & Venus. Just look towards the South-West to see all three.

The occultation of Venus will begin a few seconds before 15:50 GMT, disappearing behind the dark (in shadow) side of the Moon in just 40 seconds!

Even though this event begins in daylight, you will still be able to see it with your own eyes, through binoculars, or through a small telescope. To find the Moon, just look towards the South. Make sure that you do not look anywhere near the Sun to the West. Looking towards the Sun can do serious long-term damage to your eyes.

The Moon finally uncovers Venus once again at 17:19:15 GMT, and it takes Venus about 40 seconds to re-appear.

By the time Venus re-appears, the Sun is below the horizon and it is dark. So it promises to be an interesting sight to see the bright Venus slowly re-appear from behind the Moon! Although, when it does so, the Moon and Venus will only be 8 degrees above the horizon as seen from Greenwich.

As shown in the lower-right image, Jupiter is also visible, just to the top-right of Venus and the Moon.

The International Space Station can be seen flying over the UK during the next week. And, since it has solar panels the size of a football field, it is very bright and very easy to see - weather permitting, of course! The times (in GMT) of when the station flies over the UK are as follows (if you live elsewhere, take a look at SpaceWeather.com satellite flyby website)...

The disappearence time is when the space station flies into the shadow of the Earth, and that sometimes occurs when the space station is directly over head (such as on the 29th of November).

The Space-Shuttle is currently docked with the Space Station, but on the morning of Friday the 28th, the pair seperate. So when you look after the 28th, you will not only see one bright point of light, you will see two - the Space Shuttle chasing the Space Station!

Did you manage to see the Moon hide Venus on Monday night?

Unfortunately, the weather was not kind to us here in Greenwich, with thick cloud rolling in just minutes before the occultation began. However, we did manage to get a few photographs, just before the cloud came in.

Royal Observatory Astronomers Darren Baskill & Tony Sizer managed to grab the following photographs.

Although the clouds did spoil our view of the Moon and Venus, they did manage to provide a beautiful sunset. This was the view from the Royal Observatory South building, about 10 minutes before the occulatation was due to start.

There are only a few more chances left to see the International Space Station fly over the UK before the new year. The following times are when the station is flying over the UK (if you live elsewhere, take a look at SpaceWeather.com satellite flyby website)...

The Moon, Jupiter and Venus have been a beautiful sight over the last few evenings. Here are some photographs showing the view from Greenwich.

On the evening of the 2nd of December, we had the following view... notice the seperation of the Moon and thew two planets.

Just a day later, and the Moon has move a significant distance in the sky, as it orbits around the Earth. The following photograph shows the view on the evening of the 3rd of December, 2008.

This final photograph was also taken on the evening of the 3rd of December. What a beautiful sight we have been treated to over the last view days!

We have very long nights in the northern hemisphere during December - perfect for astronomy! Here in Greenwich, the sun is setting at 4pm in the afternoon and not rising again until 8am - giving 16 hours when the Sun is below our horizon. When you take evening and morning twilight into account, we have 14 hours of beautiful star-filled darkness... if you can get far enough away from light pollution.

The long nights are due to the Earth being tilted by 23.5°. In December, the northern hemisphere of the Earth is pointing away from the Sun, so the Sun appears much lower in the sky, and its warmth is diminished.

Jupiter & Venus are the highlights this month, visible low in the west in the evening sky, just after sunset. While Jupiter stays low throughout the month, Venus gets higher in the evening sky every day, as it orbits around the Sun.

And on the 27th of December, Venus is next to Neptune, making Neptune unusually accessible. Just find Venus, the brightest thing in the sky, and then look to the top-right slightly (about two finger widths at arms length) and see if you can see Neptune. If you live well away from any light pollution, you may be able to see it with you own eyes (although it is at the very limit of human visability!); otherwise, try using binoculars or a telescope.

It is also the time of year when we are further away from the centre of our Milky-way galaxy, and the galactic centre is hidden behind the Sun.

In the early evening around 6pm, we look westwards to see the patch of sky that used to be directly above us in winter. So, ironically, the Summer Triangle is visible throughout winter! In fact, from the UK, Deneb is a circumpolar star - meaning that it never sets below the horizon.

During December, we have four hours after sunset to see the Triangle before it follows the Sun below the horizon. By February however, you will only be able to see the Triangle in the early morning sky, just before sunrise. Read last months' posting to read about the interesting objects in the Summer Triangle.

Look East in the evening, and you are looking directly out into deep space, towards the constellation of Orion. At the bottom of Orion, to the left of Rigel, is the Orion nebula - a cloud of gas and dust, collapsing to form the latest generation of stars, recycling materials from old, now dead, stars. And you can see that for yourself with binoculars.

Here's to dark and clear skies in December!

The movie below shows how Jupiter, Venus & Mercury will look at 5pm in the evening sky everyday throughout December 2008, as produced using the excellent (& free!) planetarium software Stellarium.

At the start of the month, the brighter Venus is to the left of Jupiter - both are easily visible with the unaided eye in the evening twilight. Between 4pm and 5pm is the best time to look.

As December progresses (see the date in the top left corner), Venus gets higher and higher in the evening sky. As the Earth orbits around the Sun, it is moving to the opposite side of the Sun to Jupiter - which is why Jupiter appears to be moving towards the Sun. Just after Christmas, Mercury comes into view as well.

New Year's Eve is the highlight, however, with Jupiter and Mercury being VERY close together in the twilight sky, as well as the Moon and Venus!

This movie shows how we will see the planets "dance" during December (2008). First off, we see the view that we will have when we look towards the South-West. The movie then plays again, this time retaining the 'old' positions super-imposed so we can see exactly where the planets have moved from. Finally, these two scenes are repeated for convenience.

To understand why the planets are moving around as they do, take a look at the view from above...

This image was produced using the free Celestia software. The yellow arrow indicates which way all the planets orbit around the Sun, and note that the planets closer to the Sun orbit much quicker than the planets further out. Mercury wizzes around the Sun in just 88 days; Venus in 225 days; the Earth in 1 year; and Jupiter takes almost 12 years to orbit the Sun!

From above, we can see that, as the Earth orbits the Sun, Jupiter begins to be hidden by the glare of the Sun as the Earth moves to the opposite side, while Venus & Mercury become easier to see as they get further away from the Sun.

After seeing all this movement, it is hardly surprising to learn the origin of the word 'planet' - it's ancient Greek meaning wanderer!

Today, the 12th of December 2008, we have the earliest sunset of the year in the Northern hemisphere. In Greenwich, the Sun sets at 15:50GMT.

The earliest sunset occurs on a different day to the solstice due to a combination of the Earth's elliptical (oval-shaped) orbit and it's tilt. Put together, these two effects are known as the Equation of Time, the difference between what an averaged mechanical clock will say and what a Sun dial will say.

On Friday the 12th of December, we have the biggest Full Moon for 15 years!

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The Moon orbits the Earth in an elliptical (oval-shaped) orbit, and during tonight's full Moon, it will be closer than usual - only 356,600km away from Greenwich! (which is about 363,000km away from the centre of the Earth).

On average, the Moon is 378,000 km away, and at furthest, it is 399,300 km away from the Earth's surface. So tonight's full Moon is 6% closer than average, and so 11% brighter than average! (Or, to put it another way, it is 11% bigger & 20% brighter than when the Moon is at its furthest point away from us).

Like last month, the Moon will be drifting past two planets on its Moonthly orbit around the Earth. Unlike last month, the Moon will be passing by a different pair of planets!

Last month, the Moon drifted past Venus and Jupiter, forming a wonderful smiley face in the evening sky! This unique event was witnessed around the world,and Naveen L Nanjundappa, Vice President of the Bangalore Astronomical Society, took the wonderful photograph below (many more photographs are on the BBC News website, and SpaceWeather.com).

This month, the Moon will be passing by the planets Jupiter and Mercury on the 28th and 29th of December. Their exact alignment and the best time to look will depend on your location, but the three will be close to each other. For the UK, the best time to look is on the evening of the 29th, just after sunset (4.30pm is the best time), low to the South-West, when the crescent Moon is just to the top left of the bright Jupiter, and slightly fainter Mercury.

In fact, for just a brief period after sunset on the 29th, the Moon is so close to Mercury that it actually hides it! (an occultation) Unfortunately, that event will only be visible from a small region of the Pacific Ocean, a few thousand miles East of Japan!

However, for people living in western/central Australia, just after their sunset (which occurs 6 hours later than Eastern Japan), they will get to witness the Moon covering Jupiter instead!

It just goes to show what a difference a few thousand miles can make!

On new year's eve, the Moon will have moved along to Venus, higher and brighter than both Jupiter and Mercury. To see where the planets will be every night, take a look back at my December's Dance of the Evening Planets post.

The Meridian laser marks the route of the Greenwich Meridian by night in a northerly direction from the Observatory at Greenwich.

People often ask us: from how far away it can be seen? Not surprisingly, the answer to this is highly dependent on the weather and the atmospheric conditions at the time. But under good conditions it's a lot further than you might imagine. The furthest at which it has been reliably sighted with the naked eye is at a distance of 36.7 miles from Periwinkle Hill a couple of miles to the south of Royston.

In order to see the beam when more than a few miles away from the Observatory, you need to be standing directly beneath it (and definitely no more than a few hundred yards or so to either side), and looking south, back along the beam towards Greenwich. There are a number of elevated sites in Cambridgeshire to the north of Royston with good horizons to the south. My good friend and former colleague Robin Catchpole visited one such a site at Lolworth (a small village just to the south of the busy A14) at the end of last year. Although not visible to the naked eye, Robin was able to see the beam with his binoculars and photograph it with his compact digital camera. During the first weekend in January, when much of southern England was enjoying clear days and frosty nights, I joined Robin on the Saturday evening to go laser hunting slightly further to the north in the village of Bluntisham at a distance of 60.5 miles. Once again, the laser was visible but once again, only though binoculars ... and here's the picture that Robin took to prove it.

At this sort of distance from the Observatory, the visibility of the beam is highly dependent on the state of the atmosphere at all points along its route and unfortunately for us, within just a few minutes of our arrival the beam disappeared from view. Under exceptional conditions, I would hazard, that it would be possible to see it from as far north as Bluntisham with the naked eye.

If you want to go laser hunting yourself, you will need either a suitable Ordnance Survey (OS) map and or a GPS. Because of the way the maps are constructed, the Meridian doesn't run vertically up the page. Instead it curves slightly from right to left. Although most OS maps do not specifically mark the Meridian, it is possible to determine more or less where it runs by making use of the graticules (the small blue crosses) that are generally marked every 5' of latitude and longitude on the Landranger maps - the ones with the purple covers. What you will need to do, is look along the top edge of the map where the longitude scale is marked until you find 0^o and then look down the page for the corresponding graticules. What you may also find useful (especially if you need to use binoculars), is a magnetic compass to help orientate yourself in approximately the right direction. The Periwinkle Hill site can be located fairly easily even if you don't have an OS map or GPS as the beam passes almost directly over the transmitting tower that is located there.

Whatever the weather, the Observatory at dusk is always a pretty amazing place to be, not least because of the fabulous views across London. Unlike last night when it was misty, the skies were really clear when I snapped this shot of the Peter Harrison Planetarium on Tuesday.

As it happens we had an Evening with the Stars running that evening and our visitors had a real treat as they looked though the 28-inch telescope. If you are interested in looking through it yourself, there are more sessions scheduled for later this month and into March.

We took advantage of the change in the weather yesterday afternoon to check the alignment of the Meridian laser (see Monday's posting). Arriving in Chingford at around 17.00, we had completed our adjustments by 17.30. The picture below was taken about ten minutes later.

With next Monday's new moon, comes not only Chinese New Year, but also an annular eclipse of the Sun. Annular eclipses are more common than total eclipses, but fewer people are aware of their existence. Both occur when the Moon passes directly in front of the Sun. But in the case of an annular eclipse, the disc of the Moon is not large enough to cover the Sun completely. The last annular eclipses to be visible from Britain were on 31 May 2003 and 8 April 1921. The next is not due until 23 July 2093. None of next Monday's eclipse will be visible from Britain and it will probably be seen by relatively few people - not least, because most of its path is over the ocean. The picture below was taken in Spain by Darren Baskill during the annular eclipse on 3 October 2005.

The image above shows the skies above Greenwich around 10pm on the 15th February, taken from Edwin Dunkin's 'The Midnight Sky'. This view is facing south with the Royal Observatory in the centre.

The wonderful constellation of Orion dominates the winter skies and can be seen from first darkness towards the southern part of the sky throughout February. Orion represents a hunter, and can easily be spotted by the three bright stars that make up his belt, seen in the centre right of the image above. Just below these belt stars, in Orion's sword, you may be able to spot a small fuzzy patch called the Orion Nebula. It doesn't look like much to the naked eye, but as this image shows, with a large telescope the sight is amazing.

The Orion Nebula is a region of star formation in our own Galaxy, a huge cloud of gas and dust being pulled together by gravity into clumps, which get denser and denser and hotter and hotter until nuclear reactions begin, and a new star is born.

We can see a group of young stars, formed within the last 100 million years, if we follow Orion's belt to the right, past the bright red giant star, Aldeberan (the eye of Taurus the bull) and on to a small cluster of stars called the Pleiades. The Pleiades are also known as the Seven Sisters, because the seven brightest stars stand out most clearly in the night sky. In fact the Pleiades contains over a thousand stars, which all formed together from a single cloud of gas and dust. Over time the Pleiades stars will gradually move apart, spreading out into space.

In the constellation of Orion itself we see some older stars, heading towards the end of their lives. Towards the bottom right of Orion is hot blue Rigel, a blue supergiant star, 17 times more massive than the Sun. In the opposite corner is cool, red Betelgeuse, a star which has cooled and bloated out so much that if it was placed at the centre of the Solar System, it would reach out as far as the orbit of Jupiter. Some day soon, Betelgeuse will end its life in a massive explosion called a supernova. Of course in astronomy, soon can be a very long time, but Betelgeuse could go bang within our lifetimes, and really would be a spectacular sight, brighter than a crescent moon in the sky.

Following Orion's belt to the bottom left we find the brightest star in the night time sky, Sirius, part of Orion's hunting companion Canis Major, giving it the alternative name, the Dog Star. Sirius is actually a binary star system consisting of a white main sequence star and a small, faint white dwarf.

As well as these fantastic winter objects, there are also some planets to be seen in the sky this month. First of all, the unmistakable Venus, visible towards the south west in the evening skies throughout February. Venus is so bright you can really only mistake it with the headlights of an aeroplane, and is at its brightest on the 19th of February. It should be above the horizon until around half past nine throughout the month.

Rising later in the evening, in the constellation of Leo, is Saturn. By the end of the month it will be rising in the East by around 6:30. Saturn is normally a stunning sight through a small telescope, with its amazing rings, but at the moment we observe these almost edge on, so they are very difficult to spot.

In the morning skies you may just spot Mercury, although it will almost be lost in the twilight. On the 13th February it reaches its greatest elongation, the maximum apparent distance from the Sun in the sky.

While researching a book I've been writing on the history of the telescope, I've come across a number of humorous prints like this one, Robert Sayer's Viewing the Transit of Venus of 1793.

It is one of the many satirical prints produced in England in the 18th century and seems to show a well-heeled couple observing Venus as it passes between the Earth and the Sun. So at first glance this appears to be just the sort of message that science's supporters were putting out - that science was worthy of study by the more learned and 'polite' members of English society.

But if we look closer, something rather different is going on. The scene isn't topical at all - the most recent transit of Venus had taken place over twenty years earlier in 1769. And the statue of the satyr on the right hints at rather more sexual interests, emphasised by the way in which the man lightly fingers the telescope, suggesting that it is akin to what contemporaries called the 'staff of life'. Perhaps he is hoping for a more bodily transit of Venus, recalling stories of the amorous encounters of the Greek goddess of love. This telescope, then, has become a most impolite instrument.

Keep coming back for more Telescopes stories throughout the International Year of Astronomy 2009.

In the news this week you may have read that the Monument near London Bridge has just reopened after restoration work. This large column was erected next to the Thames as a memorial to the Great Fire of London of 1666, and was completed in 1677. But what is not so well known is that its designers, Christopher Wren and Robert Hooke, intended it to be used as a telescope.

The Monument was designed as a type of telescope known as a zenith telescope, used to observe stars that pass directly overhead. Wren and Hooke hoped that by looking at one star in particular they might be able to detect stellar parallax - a change in the position of an observed object caused by a change in the observer's position. This was something that should be observed if the Earth was moving around the Sun, but astronomers had not yet been able to detect it. In fact, it was only in the nineteenth century that stellar parallax was finally observed.

Here, the whole structure was the telescope. The observer sat in a room in the basement and looked up through the 'tube' created by the spiral staircase. The flaming urn on top had a hinged lid that opened for viewing. Sadly, it didn't prove to be up to the job because it expanded and contracted in different temperatures and swayed in the wind. Try not to think about that if you go up it!

I'll be blogging about telescopes regularly throughout the International Year of Astronomy 2009, revealing some of the stories behind real and imaginary instruments from the National Maritime Museum collections and elsewhere.

The Monument, from John Stow, A survey of the cities of London and Westminster

Astronomy Now's Greg Smye-Rumsby explains how to see the Lyrid meteors tonight and tomorrow night.

Mercury, the closest planet to the Sun, makes a rare appearance in the early evening sky at the moment. If you look just north of west, at about 9pm, you should see Mercury as a bright point of light above the setting sun. This photo shows Mercury, captured in conjunction with the new crescent Moon and the Pleiades star cluster, above Canary Wharf on Sunday evening.

While looking into the history of the telescope, I've been struck by the number of images that, perhaps unsurprisingly, show it symbolically as an instrument of revelation and learning. One of my favourites is this detail from the frontispiece to Johannes Hevelius' Selenographia of 1647.

Hevelius (1611-87) was from a brewing family from Danzig (now Gdańsk, Poland), gaining further riches from his marriage to Katharine Rebeschke, whose family lived next door. Being so well off, he could indulge his passion for astronomy by building large telescopes for his personal observatory, which spread across the city's rooftops. One of the things he did there was to spend four years making detailed, and very beautiful, maps of the Moon, which he published in the Selenographia. His very fine observing skills and artistic talent, not to mention the quality of his telescopes, meant that these were the best lunar maps available for a century.

This detail from the book's frontispiece symbolically shows how the telescope fitted into his work and thinking.

In the centre is the figure of Contemplatio, covered in eyes and carried aloft by an eagle. Both these figures are significant. 'Contemplatio' can be translated as contemplation, but also as viewing or surveying, while the eagle represents both vision and ascension. Contemplatio is also holding a telescope in her right hand and is using it to sweep away the clouds of ignorance. Behind her are the Sun and Moon as revealed by the telescope, with sunspots clearly visible. Beneath Contemplatio, two putti hold a banner with a biblical quotation from Isaiah, which translates, 'Lift up your eyes on high and behold who hath created these things.' To Hevelius, then, the telescope is an instrument that reveals the truth about a (Christian) created universe, the contemplation of which is a spiritual journey in itself . His telescope is a weapon of intellectual and spiritual advancement.

If you are interested in Johannes Hevelius and his astronomical work, you can find out more at our forthcoming conference, The Long View.

The Perseids, one of the best-known and most spectacular annual meteor showers, peaks this year between 12-13 August.

The best times to view from the UK will be in the early morning hours of Thursday 12th and Friday 13 August, between about midnight and dawn. Weather permitting, viewing conditions should be ideal this year with the recent new Moon (10 August). At the maximum there could be over 80 meteors per hour.

The Perseids is a bright meteor shower associated with comet Swift-Tuttle. As the Earth's orbit passes through that of the comet, tiny dust particles in the comet's wake are swept up by the Earth, entering the atmosphere at speeds of over 215,000 km/h and burning up. This produces the effect that we see as 'shooting stars' - meteors.

Perseid meteors can be seen during late July and early August, falling off rapidly after a peak around 12 August. It's thought that the shower as a whole may be about 160,000 years old but the majority of what we can see is 5000 years old.

The 'radiant' of the shower (the point from which meteors appear to emanate) is the constellation Perseus, hence the name. The meteors can appear in any part of the sky, but the best place to look is usually about 1-2 handspans from the radiant, quite high in the northeastern sky.

In clear weather, you should be able to spot a meteor every few minutes or so. Most appear as flashes of light lasting less than a second, but some may be more dramatic and leave more persistent trails. NB your eyes will take about 20 minutes to adapt to the dark. You'll need to scan the sky for the random flashes so it's best not to use a telescope.

Meteor showers are never completely predictable, and last year there was a second peak nearly a day after the main one.

More information about this meteor shower can be found in the Royal Observatory's Perseids fact file.

*Times are BST not GMT, and may not correspond exactly with the official (religious) sighting of the crescent moon.

You can get information on the visibility of the Moon from anywhere in the world from HM Nautical Almanac Office's Websurf facilty:

• accept the conditions of use (Websurf homepage)
• select the 'Moon-Viz' link
• choose or search for a place
• select a date range
• The visibility information (time) is in the 'BEST TIME' column; Moon set time is in the 'Moon set' column. (NB add +1 hour for BST.)

• Moonsighting.com - provides moon visibility curves for the current year and next year.
• Astronomical Applications Department of the US Naval Observatory (USNO) - lists New Moon birth times for the whole year. Note, the crescent Moon will not be visible until at least 15 hours after the birth of the New Moon. The USNO also has a page dedicated to the visibility of the crescent moon and the Islamic calendar.
• You can help astronomers improve their predictions by joining in the Moon Watch project. Look out for the new crescent moon and submit the details to the Moon Watch website.

Two planetary conjunctions involving Saturn are visible from the UK this month. However, they will be very low in the eastern pre-dawn sky and there won't be much time to observe them before it gets too light to see them easily with the naked eye.

In the early morning of 8 October Mercury will be 0.3º from Saturn in the sky, and at 11.00 in the morning of 13 October Venus will be 0.5º from Saturn. These two events effectively form a triple conjunction or what some are describing as a 'three-way planetary dance', visible between 8-16 October. On 16 October they will be joined in the pre-dawn sky by the waning Moon.

Astrologers seem particularly excited about the multiple conjunction (though ideas as to its significance vary considerably) and some astrology blogs actually have more detail about the exact timings of the events than astronomy sites.

Then on 21-22 October the annual Orionids meteor shower reaches its maximum, with a likely average of 25 meteors per hour at its peak. However, recent years have produced much stronger showers so the rate could be even higher. The Orionids are fast meteors with fine trains, associated with Halley's Comet. Conditions for observing should be favourable and moonlight will not be a problem.

Leonids

The annual Leonids meteor shower should now be visible and is due to reach its maximum on Wednesday 17 November. Astronomers expect about 10-20 meteors per hour at the peak, which is low to average for this shower. Best viewing time is likely to be the early hours of Wednesday morning, particularly after the Moon sets at around 4.00 am. As always, best meteor viewing needs dark skies away from city lights.  

About every 33 years (the period of Tempel-Tuttle), the Leonids produce meteor 'storms' when hundreds or even thousands of shooting stars can be seen. Such storms were seen in 1799, 1833, 1866, 1966 and 1999-2001 (although the expected 1899 and 1933 storms were disappointing). The 1833 storm was particularly spectacular, with an estimated 100,000 meteors per hour. The 1999-2001 storms produced about 3000 per hour.

Taurids and α-Monocerotids

As well as the Leonids, there is also the more minor Taurid meteor shower pair (Southern Taurids and Northern Taurids). The main peak is coming to a close now on 12 November, with a rate of about 8-10 meteors per hour, but the showers continue until about 25 November, their radiants moving slowly eastward across the constellation Taurus.

Image: Leonid shower; photo by Thomas Paulech and Juraj Toth, Bratislava, Slovakia

According to NASA the following sightings of the International Space Station (ISS) are possible from London, UK between Saturday 24 April and Thursday 6 May 2010:

Data from NASA's Satellite Sighting Information page (London)

See also possible sightings from all UK locations or choose your country at NASA's Sighting Opportunities page.

*Times are BST not GMT, and may not correspond exactly with the official (religious) sighting of the crescent moon.

The dates of Ramadan and other Islamic months depend on the sighting of the new crescent Moon.

Information on the visibility of the Moon from anywhere in the world is available from HM Nautical Almanac Office's Websurf facilty:

• - accept the conditions of use (Websurf homepage)
• - select the 'Moon-Viz' link
• - choose or search for a place
• - select a date range
• - The visibility information (time) is in the 'BEST TIME' column; Moon set time is in the 'Moon set' column. NB add +1 hour for BST.
   

Also of interest

• - Al Hijra and the Islamic Calendar - fact file
• - Persian astrolabe - a beautiful astrolabe dating from 1070AH by the Islamic calendar, and including a grid for finding the direction of Mecca from a number of different towns and cities.
• - Arabic (Islamic) brass globe - 18th-century globe showing all 48 constellations that were known to the Ancient Greeks, and engraved with the Arabic names of some of the stars.
• - Transmission of knowledge - as Islam spread across Northern Africa from the 7th century, it helped change the purpose of astronomy: for example, it was now needed to produce accurate tables of prayer times.
   

On 20 October 2010, Comet Hartley 2 (103P/Hartley) will pass within about 11 million miles (0.12 AU) of the Earth. This will be its closest approach since it was discovered in 1986, and one of the closest approaches of any comet in the last few hundred years. At this time, the comet should be visible in the constellation Auriga.

Image: Hartley 2 in Cassiopeia, 28 Sep 2010 (crop). Credit: NASA/MSFC/Bill Cooke, NASA's Meteoroid Environment Office.

Astrophotography opportunity

There will be a great opportunity for astrophotographers between 7-9 October as the comet passes close to the beautiful Double Cluster in Perseus. It is then expected to pass near the open cluster NGC 1528, also in Perseus, by 14 October. Don't forget to enter your photographs of the comet in the 2011 Astronomy Photographer of the Year competition which opens in January.

Viewing Hartley 2

Meanwhile over the next few days Hartley 2 should become increasingly visible with the aid of binoculars or a small telescope, and possibly even to the naked eye.

The comet is diffuse (its light is spread out over a wide area) so to see it you need a dark sky location free of city lights. The technique of averted vision - looking slightly to one side rather than straight on - is also helpful in locating faint objects. The comet will probably appear as a grey smudge of light or as a faint, fuzzy star. Heavens-Above.com has a useful locator chart.

After 10 October the Moon will start to make it harder to see the comet, so until 20 October best viewing time will be after moonset.

EPOXI mission

On 28 October, the comet will reach perihelion (closest approach to the Sun). Finally, on 4 November, NASA's EPOXI mission (previously Deep Impact) will fly by the comet, with a closest approach of 435 miles.

It's estimated that Hartley 2 will next come to perihelion in 2017, around 20 April.

13 December 2010 - Clouds permitting, don't forget to look out tonight and tomorrow for the last major meteor shower of the year. The Geminids are due to reach their peak at 16.45 UT on 14 December, as the Earth ploughs through a stream of debris left behind by asteroid 3200 Phaethon. The fragments burn up as they hit the Earth's atmosphere causing the shooting stars, some reaching the size of big fireballs.

The Geminids shower seems to be intensifying each year, and an average of about 100 meteors per hour are expected to radiate from near the bright star Castor.

Hot on the heels of yesterday's total lunar eclipse, a partial solar eclipse will be visible from the UK on the morning of 4 January 2011. The next solar eclipse visible from the UK will not be until 20 March 2015.

The partially-eclipsed Sun will rise in the south-east a little after 08.00 and the eclipse will end around 09:30. The greatest eclipse will be seen from northern Sweden at 08.50.

The table below shows details of eclipse times and magnitudes for various UK cities:

The best viewing locations with longest viewing time, greatest obscuration and greatest magnitude are in southern and eastern UK, declining towards the north and west.

Viewing the eclipse

The safest way to view an eclipse is via optical projection, such as a pinhole projector. The following links from Exploratorium explain how to make two kinds of projector and also how to obtain safe filters:

• Making a pinhole projector
• Other optical projection and filters

Image: Partial solar eclipse, 3 October 2005, taken through a solar filter. Mike Dryland, Flamsteed Astronomy Society

The first meteor shower of the year is underway and peaking at the moment. The Quadrantids is one of the most spectacular but brief showers of the year, at its peak producing 60-120 meteors per hour.

Meteors, popularly known as 'shooting stars', appear as fleeting streaks of light and most are caused by particles no bigger than grains of sand. These collide with the Earth's atmosphere at up to 70 km per second (157,000 mph) and burn up. With patience, meteors can be seen on any night of the year.

The Quadrantids

All the meteors in the Quatrandid shower appear to come from the same point in the sky, or radiant, situated near the familiar grouping of the Plough. The shower is named for the former constellation Quadrans Muralis, the stars of which once lay in that direction. The Quadrantids are less well-known than many other meteor showers, probably because only the hardiest observers brave the cold January nights.

In contrast with many meteor showers, the Quadrantids are not obviously connected to a particular modern-day comet but some astronomers believe them to originate from a large cometary body that broke up thousands of years ago.

In 2003, SETI institute astronomer Peter Jenniskens suggested that the Quadrantids are tied to the near-Earth asteroid 2003EH1 (see Dr Jenniskens' paper here). Dr Jenniskens believes this object is actually an extinct comet, possibly once seen by the Chinese 500 years ago in 1490. The comet may have subsequently broken up, releasing all its volatile material in a single event. When the Earth passes through the dust cloud each January we see the meteor shower.

Viewing meteors

Unlike many astronomical objects, observers need no special equipment to view meteors. The sensitivity and wide field of view of the human eye are perfect for watching the Quadrantids and all observers need to do is watch the sky for a few minutes. 

As ever, it pays to leave the lights of the city behind and rural sites will offer the best view of the Quadrantids, but (weather permitting) they should be clearly visible all over the UK. 

The next major meteor shower of the year will be the Lyrids, which peak around 22 April. Find out more about annual meteor showers in our fact file.

Image: Meteors in the Quadrantid shower in January 1995. The image superimposed many video frames to illustrate the apparent origin of the meteors from their radiant. Credit: Sirko Molau, IMO, Archenhold-Sternwarte, NASA.