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

Don't forget that our clocks will return to Greenwich Mean Time this Sunday morning (the 28^th of October).

This means that we have to turn our clocks backwards one hour... but we do get an extra hour in bed on Sunday morning to make it all worthwhile!

For full details, please see our Time and timekeeping page.

For 84 years the major global news headlines of the day have been preceded by the six Greenwich Time 'pips'. When the news of Neil Armstrong’s first steps on the Moon, President John F Kennedy’s assassination, and the destruction of the Berlin Wall were broadcast across the world on the BBC, they followed the familiar sound of the Greenwich pips.

The six-pip Time Signal was introduced on 5 February following the successful broadcast of the chimes of Big Ben to usher in the new year of 1924. Late in 1923, Frank Dyson, ninth Astronomer Royal, visited John Reith, Director General of the BBC, to discuss the idea of public time signals being broadcast. The six-pip Time Signal (pips for seconds 55, 56, 57, 58, 59, 60) was Dyson’s brain-child, devised in discussion with Frank Hope-Jones, inventor of the free pendulum clock, who had originally advocated a five-pip signal.

In 1939, the six-pip signal and the Time Service moved from Greenwich to the magnetic observatory at Abinger in Surrey. They then moved to Herstmonceux, Sussex in 1957. In 1990, the Greenwich Time Signal transmitted its last pips. Since then the BBC has originated its own pips based on signals from the GPS satellite network and from the 60kHz radio transmitter at Anthorn, Cumbria, operated by VT Communications under contract to the National Physical Laboratory.

The original clock used for the six-pips signal is in the Time and Greenwich gallery at the Royal Observatory. This is currently closed for redecoration, but will reopen on 1 March 2008.

The clock is regulator number 2016 by Dent of London. It was made in 1874 for use across the globe when observing the Transit of Venus astronomical phenomenon that year, before moving to Greenwich. It was the very first to provide the six-pip signals in 1924 with pendulum roller contacts, which are still in the Observatory collection.

Time by Wire: 175 years of the Greenwich Time Service David Rooney The Institute of Engineering and Technology 3 December 2008 >> go to webcast>> recommend to friend

David Rooney, Curator of Timekeeping at The Royal Observatory, Greenwich was honoured to give The Wheatstone Lecture 2008. In his lecture, David Rooney explored the curious history of time distribution from Greenwich, revealing little-known stories behind one of Britain's best-known measurement systems: Greenwich Mean Time.

Today is Chinese New Year and sees us saying goodbye to the Rat and hello to the Ox. But, while most of us are relatively familiar with the idea of animals marking the 12-year cycle of the Chinese calendar, we probably know less about how this calendar works.

It is a luni-solar calendar, meaning that it is based on the apparent motions of both the Moon and the Sun. Because the lunar months (29.5 days) do not match the solar year (365.25 days), there always several days 'left over'. This problem is solved by adding an extra, intercalary month seven times in every 19 years. The Chinese new year moves around (between 20 January and 19 February) in our calendar because it is timed to coincide with the first new moon after the winter solstice.

The 12 animals assigned to the years reappear elsewhere in Chinese calendars and astronomy. They are used to represent the 12 ordinary months, a cycle of 12 days and even two-hour periods within each 24-hour day. In astronomy, the animals are associated with the stations which Jupiter passes through in one revolution around the Sun (an 11.86-year cycle) and yet another association is with compass directions. Chinese compasses and sundials in the Museum collections therefore include the characters for the animals.

Families will get a chance to have a closer look at instruments like this during half-term (20 February 2008) when I will be displaying and talking about them at the ROG. You can find about more about details of this and other Chinese New Year events at the museum.

This week H1 is to be dismantled for repairs in the conservation workshop here at the Royal Observatory. The Harrison timekeepers are so popular that they're rarely off display.

Harrison's first timekeeper, H1

The problem with the timekeeper occurred last year when the connection broke between one of the balances and its lower balance spring. The balances and springs are the vital 'beating heart' of the timekeeper, and being complete and well adjusted is fundamental to the good going of the instrument.

H1's right balance and its broken spring connection

As Senior Specialist in Horology at the Museum it's my job to undertake this exciting and delicate work, and it was with some trepidation that we prepared H1 for its 40 metre trip yesterday morning to the workshop. It's now on the 'operating table' (a medical trolley we use for transporting) and my first task is to take photographs all round the timekeeper before any dismantling takes place.

During the work, there is a screen set up in H1's showcase with a short slide show telling visitors what's happening. If staffing allows, the on-going work on H1 can be seen from the Time for the Navy gallery, which is next to the workshop and has a glass-backed showcase through which parts of the workshop can be viewed.

Working on H1 is going to be very special for me as one of my great heroes in the Harrison story is Lt.Cdr R.T.Gould, who rescued the timekeepers from oblivion back in the 1920s and 30s. It was almost 90 years ago, in 1920, that he first started that work. I'll be contributing two or three entries a week to this blog, so keep an eye out if you're interested!

Dismantling of H1 has progressed smoothly this last week, and there has been considerable interest in the project from colleagues and the public. Last Thursday the Guardian newspaper's delightful Maev Kennedy paid us a visit with photographer David Levene, and an extraordinary double page 'centrefold' picture appeared in the paper on Monday with H1 pictured from a fascinating and engaging angle. If I'd known my rough notes, visible next to the timekeeper, would be readable in a national newspaper I'd have tried to make them less inscrutable!

Also on Monday we had a visit from the current students and tutor, Matthew Read, from the Clock Course at West Dean College, who were duly impressed by being able to inspect H1 partially apart, and were consequently able to better understand some of its intricacies.

So far, the dials are all off and the front plate has been removed, revealing the 'motion work' (the gears which ensure the hands go round at the correct rate). The calendar wheel had a particularly lovely surprise, in that I found Harrison had decorated the little part on the wheel called the 'jumper' with a most beautiful, rather Celtic style tail and with a front end shaped in the form of a little bird's head!

None of this can be seen when the clock is complete of course, and it must have been included entirely to please himself, and future clockmakers. Well, it certainly pleased me John!

Next will be the main train of wheels and all their roller bearings; it will be interesting to see if much wear is evident after nearly half a century of virtually constant running.

Dismantling of H1 has progressed well and the timekeeper is now almost totally in pieces. As parts come off I'm taking the chance to look at them closely and am developing a much more detailed idea of the restoration carried out by Gould and the Chronometer Section in the 1960s.

In spite of his descriptions of the restorations in his notebooks, Gould did not provide complete data, and I am now busy counting teeth on wheels, measuring parts and keeping a tally of the total number of parts in H1. Some statistics are proving quite surprising. For example, just the two fusee chains (which link the driving springs with the wheels of the clock) between them total almost 4,000 bits!

Now that the wheels and roller bearings are all out it is becoming clear that the timekeeper is in very fine condition. Almost no wear is perceptible on the bearings, and Harrison's 'rolling contact' arrangement has stood the test of time extremely well. The only evidence of long use is what one might call the 'computer mouse' problem, where the rolling contact has caused thin layers of dust to become compacted on the rollers (just as it does inside the mouse sometimes).

Next is extensive photography and measuring, and I have to decide on the best (and most conservative) way to repair the broken balance spring connection.

This Sunday sees the 150th anniversary of the starting of the Great Westminster Clock, popularly known as Big Ben after its great bell. While Parliament is enjoying this anniversary (see http://www.bigben.parliament.uk/), it seems timely to remember the ROG's connection to these events. 

Edward John Dent, engraving by Charles Baugniet, 1853.

 
The Westminster Clock was built and designed by Edward John Dent, who made many of the clocks used by the ROG and now in the NMM collections. His recommendation as maker, and much of the design was, however, suggested by George Biddell Airy, the 7th Astronomer Royal. 

George Biddell Airy, engraving by Thomas Herbert Maguire, 1852

Airy had frequently collaborated with Dent on Observatory equipment and to try out his own ideas in clock-making theory. Not least, they had already collaborated on another important turret clock, which was made for the Royal Exchange. This was so successful that Dent remarked, "The mechanical world in my opinion lost its greatest genius when Mr. Airy became an Astronomer....".
 
Perhaps most importantly, from the ROG perspective, it was Airy who drew up the specification to which both the Royal Exchange clock and the Westminster clock should conform. They were to be far more accurate than previous public clocks of this type, for Airy specified that the first stroke of each hour should be accurate to a second. This was to be regulated to Greenwich Time, by being checked twice a day at the ROG via telegraph. As historian of science Jim Bennett explains, Airy not only devoted a lot of time to these clocks, but "it is clear that his general intention was not simply that another clock should be built, but to effect a change of attitude to public timekeeping". 
 

Westminster Clock Tower, watercolour by William Lionel Wyllie (late 19th/early 20th century)

Things did not proceed quite as easily as they had with the Royal Exchange clock and, perhaps because of lack of time, Airy asked the MP and amateur clock-maker Edmund Beckett Denison to assist in overseeing the project. Differences between the two led to Airy resigning in 1853 - but his demand for accuracy and the link to GMT remained.

See the UK Parliament website for an account of the various other delays that hit the building of the clock, the tower and the bell - and you can see some fantastic images of the Clock Tower and the workings of the clock on the BBC website.

The summer solstice occurs today, 21 June, at 11.38 UTC (GMT).

The summer and winter solstices mark the times when the Sun is at its furthest from the celestial equator (the projection of the Earth's equator onto the sky). The world 'solstice' comes from the Latin solstitium meaning 'Sun stands still' because the apparent movement of the Sun's path north or south stops before changing direction.

The summer solstice does not always fall on 21 June. Because the Earth takes approximately 365.25 days to go around the Sun, the precise time of the solstices and equinoxes occurs about 6 hours (0.25 days) later each year, with a jump of a day backwards on leap years. The last time the summer solstice was not on 21 June was 1975 when it occurred on 22 June at 00.27, and in the year 2012 it will occur on 20 June at 23.09.

Find out more about solstices and equinoxes in our fact file.

Hour Angle

To mark the solstice, the Royal Observatory is hosting Hour Angle by composer John Eacott, a free musical performance sonifying the exact moment of the summer solstice. A real-time calculation of the Sun's declination will be transformed into live notation played by 12 musicians. The piece will allow visitors the chance to experience the solstice in an unforgettable way. The performance will start promptly at 12.08. Visitors are advised to arrive early.

For the last few weeks, H2 has been in the horology conservation workshop at the Royal Observatory undergoing research. The work, which is part of the continuing research for a full published catalogue of the NMM's collection of marine chronometers, involves the complete dismantling of the timekeeper. Every part is being studied, measured and photographed, the intention being to take a fresh look at Harrison's work on his longitude machines.

Last year H1 was dismantled and studied, and some interesting comparisons can now be made about Harrison's early work. It has always been believed that the simple portrayal of Harrison as a lone craftsman, was too simplistic, and we know that H1 was constructed with the help of Harrison's brother James, and almost certainly with advice and supplies from George Graham's contacts in London.

Harrison is known to have had help in his construction of H2, which was made in London, and the current study confirms this, with a much more professional feel to the materials and the finishing of this timekeeper; if H1 is a reminiscent of a fascinating 'country clock', then H2 has all the trappings of a 'scientific instrument'.

There is no doubt Harrison had help in construction, but this doesn't diminish the status of this extraordinary timekeeper, which teems with interesting 'Harrisonian' designs and construction features.

The timekeeper is now completely dismantled and before reassembly can begin there is full photography and measurement for CAD drawings to be done. Analysis is also planned on both the special alloys and the wood used in the timekeeper. It has always been said that the latter is lignum vitae, but as far as is known this has never been positively proved before.

Further updates will follow before the timekeeper returns to exhibition in the Longitude Gallery, now estimated to be sometime in late July.

Conserving the H3 Timekeeper from Royal Observatory Greenwich on Vimeo.

A short film documenting the dismantling of John Harrison's third marine timekeeper H3. It has been removed from display for cleaning and research for a new chronometer catalogue. It will be back on display in April 2011.

Conserving the H3 Timekeeper from Royal Observatory Greenwich on Vimeo.

This second installment reveals how the timekeeper is being dismantled and recorded.

Conserving the H3 Timekeeper part 3 from Royal Observatory Greenwich on Vimeo.

With H3 almost completely dismantled, Jonathan Betts reflects on his progress so far and how the project affected the last man to undertake the task.

As part of a large cataloguing project to research all the NMM's marine chronometers, I am currenmtly undertaking a close study of Harrison's third marine timekeeper, H3 (made during the 1740s). It is proving hugely interesting and revealing as can be seen in the videos which have been tracking my progress.


Marine timekeeper, H3 (ZAA0036)

The aspect I'm studying at the moment is the extraordinary (at least to me) glazed brass case of the instrument, and I'm wondering about 18th century 'instrumental' practice where glazed cases are concerned? The case (which the timekeeper fits in very closely indeed and which stands just over 60cms high) has a 'top', a middle band (attached to the timekeeper) and a 'bottom', the three parts held together round the middle with 32 screws. The whole thing is incredibly beautifully made, using cabinet-making techniques, and consists of precisely 501 parts, all fitted together mechanically, with no solder anywhere. The brass panels are just 2mm thick and the four main vertical edges are dovetailed (yes!) all the way from top to bottom with a total of 174 tiny dovetails rather in the way that coppersmiths tie plates together before soldering, but much finer and without solder. The dovetails are so well cut the vast majority cannot be seen, but I show a patch where corrosion and stress has revealed some of them (I have temporarily marked the lacquered surface with felt-tip pen to identify them).


The brass panels with dovetails

The structure inside forming the frames for the glazed panels are all pinned and riveted with 425 rivets, and the glass is then puttied in. The decorative moulded cornice is also 'invisibly' attached all round with pins, disclosed at one corner where the case was damaged in the past and was apparently heated to repair it, not very successfully.


The decorative moulded cornice

I wonder whether such large cases are unusual at this period, or are other instruments made in the mid-18th century that are housed in such cases? If so, how are they constructed? I am familiar with the 18th century grand orreries (e.g. those by Wright etc) in the lovely 'cold-frame' type wooden glazed covers, but can't think of anything in metal at this period. If anyone knows of any examples please do get in touch below.

Conserving the H3 Timekeeper part 4 from Royal Observatory Greenwich on Vimeo.

The timekeeper is now completely dismantled, but the job is not over yet for Jonathan. The case is keeping him busy and presenting surprises as well.

Conserving the H3 Timekeeper part 5 from Royal Observatory Greenwich on Vimeo.

H3 has returned to public display after a thorough cleaning and cataloguing. This video captures Jonathan's feeling about the project as well as the timekeepers move back into its showcase.

Conserving the H3 Timekeeper part 6 from Royal Observatory Greenwich on Vimeo.