In 1939, Harold Spencer Jones, our tenth Astronomer Royal wrote a paper titled: Is there life in other worlds? Spencer Jones was not only well regarded and honoured by his peers, he was also a great populariser of astronomy. So it is perhaps no surprise that in 1940, he published a popular book under the title: Life on other worlds. It gives 'a balanced popular survey of current astronomical knowledge and speculation' at that time and was described by the novelist HG Wells as a 'charmingly lucid book'.

So what did Spencer Jones have to say in his chapter Mars - the planet of spent life? He started with some of the practicalities of observing Mars and obtaining images, before going on to look at the work of Schiaparelli and the later work of Lowell. Schiaparelli was the first to observe the so called Martian Canals, whilst it was Lowell who worked up the theory that they had been created by intelligent life. Discarding the evidence on which Lowell based his conclusions, Spencer Jones went on to say that 'it is almost certain that there is some sort of vegetation on Mars'. Spencer Jones' popular books all went through many editions. If you are one of those who likes to browse through a physical rather than an electronic book, there are cheap second-hand copies available on the internet.

Probably the best known - or at least the most photographed - of the weathervanes at the ROG is that which sits on top of the time ball on Flamsteed House. But there are two others that are worth a closer look. They date from the turn of the last century and, as well as being decorative, make interesting allusions to aspects of the Observatory's history.

The first one that you come across as a visitor is on the Altazimuth Pavilion. It is modelled on Halley's Comet, as depicted in the Bayeux Tapestry. It was erected in June 1901, a few years after the building was completed but in time for the comet's return in 1909. There is a clear link with the Observatory's history since Halley was the second Astronomer Royal, although his famous prediction was made fifteen years before he took up the post. It is not clear why the illustration from the Bayeux Tapestry was used as inspiration, although its shape is ideal for catching the wind and echoes that of the weathervanes of the Royal Naval College down the hill.

Weathervane depicting Halley's Comet

The second vane is sited on top of the dome of the South Building, or the New Physical Observatory as it was once known. This building was erected in stages between 1890 and 1899, with the vane being completed in March 1897. This time the allusions to the Observatory's history are a bit less obvious, for it depicts a ship.

Weathervane on the South Building

However, it is not any old ship, but Henri Grace a Dieu, or the Great Harry, a flagship of Henry VIII that was probably the most famous historical vessel before the Mary Rose's resurrection stole the limelight (as suggested by the NMM's collection of prints of this ship.) A bit of digging brings up references that remind us that the original purpose of the ROG was to solve a navigational problem and that throughout the 19th century it was administered by the Admiralty. Henry VIII had founded the Admiralty and the Great Harry's master, Thomas Spert, was the first Master of Trinity House, a foundation that had the safety of seafarers at its heart. In addition, there is a local reference as the ship was built at Woolwich. The naval links are brought out elsewhere in these buildings, particularly in the rounded 'porthole' windows below the domes - for both were designed by William Crisp, an engineer in the Admiralty's Department of Works. The ROG's modern link with the NMM, as well as its history, means that this nautical theme is still entirely appropriate.

In the last few weeks I've been asked about Thomas Cooke (1807-1868) and whether he should be commemorated in some way. Each time my answer has been a resounding yes. Although he's not well known today, his is an inspiring story.

Born in Allerthorpe in the East Riding of Yorkshire, Thomas was the son of a shoemaker. Then in his youth he became inspired by tales of Captain James Cook (no relation) and resolved to go to sea by teaching himself mathematics and navigation. It is said, however, that his mother's tears over the dangers she foresaw caused him to change his mind and turn his attention to optics and making telescopes. This was something he became very good at. After setting set up a firm in York, he gained a worldwide reputation for the quality of his refracting telescopes (which use lenses to gather light).

Portable refracting telescope by T. Cooke & Sons, the firm Thomas Cooke created

As well as winning prizes at international exhibitions, Cooke's telescopes also proved their worth in astronomy. His work included the mount for a telescope William Huggins used for ground-breaking work in spectroscopy, the telescope Norman Lockyer used for work in the same field, and what became the largest telescope in the world (for a short while) - the Newall telescope. This had a main lens of 25 inches in diameter and was made for Robert Newall, a rich industrialist with a private observatory at Ferndean near Gateshead. Sadly, the weather there was too poor for good observing, and the telescope went to Cambridge University's observatory after Newall's death. Then in the 1950s it travelled to the Greek National Observatory in Athens, where it is still in operation.

In his lifetime, Thomas Cooke helped to bring Britain back to the forefront in optical manufacturing, an area in which German and French firms had begun to take over. His firm built telescopes of outstanding quality that were used in many professional and private observatories and which underpinned important astronomical work. His contribution to Victorian science is certainly worthy celebrating.

The 'onion' dome for the Royal Observatory's 28-inch telescope was designed and built by Cooke & Sons

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.

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