I bought a new digital camera a few weeks ago, and I was very impressed by its resolution - a whopping10 Mpx! (10 million pixels). But that is tiny compared to the digital camera involved in the University of Hawaii's Pan-STARRS project...

Their digital camera is a staggering 1,400 Mpx!

I would have to buy another 139 cameras to compete with that!

Pan-STARRS main aim is to repeatedly photograph the sky looking for potentially hazardous asteroids - we only know of 953 PHA's at the moment (according to SpaceWeather.com). Having said that, they will also be able to do lots of other interesting science as well, such as looking for variables stars (e.g. supernovae).

This project continues in the great tradition of astronomers leading the way in digital camera technology. The first CCD (a type of digital camera sensor) was used on the Kitt Peak National Observatory's 1m telescope all the way back in 1979. This CCD was 50x more sensitive than film. It took until 1990 for the first commercial digital camera became available, and now, almost everybody has one!

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.

People often ask why the Greenwich Meridian is where it is and which came first, the line or the Observatory. The short answer is that the Observatory came first and the line is where it is because of the Observatory. But it's a bit more complicated than that!

The Greenwich Meridian

A meridian is any imaginary line running from the North Pole to the South Pole. Astronomers who wanted to plot the positions of stars and planets set their telescopes up on a meridian, which they used as a reference line for their measurements and charts.

In 1850 the Astronomer Royal at that time, George Airy, ordered a new and much more accurate telescope, which he designed himself. It was much larger than previous telescopes so he had to find firms who were capable of making it.

The seventh Astronomer Royal, George Biddell Airy

For the metal castings he chose the engineers Ransomes and Sims of Ipswich. They specialised in agricultural machinery, but had some of the best manufacturing facilities in the country and were related to Airy through his mother. The lenses and other optical parts were made by a well-known firm of specialist opticians in London, Troughton and Simms. They had made other telescopes for the Observatory, so Airy was confident of their ability.

Airy's transit circle, completed in 1851

The new design was for a type of telescope called a transit circle. The name comes from the fact that it was fixed on a north-south line for the observation of stars as they crossed, or transited, the meridian. It also had a circular scale for measuring the height of the stars above the horizon. The line through the centre of this telescope became the Greenwich Meridian.

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

Today has been designated Ada Lovelace Day - an international day of blogging to draw attention to women excelling in technology. It is named after Byron's daughter, Ada Lovelace (1815-1852), the mathematician who is credited with writing the first ever computer programme for Charles Babbage's Analytical Engine, a never-completed computing machine. Taking the idea of technology broadly, I thought this would be a good opportunity to begin a series of occasional blog entries on women connected to the ROG throughout its history.

The first woman who was seriously involved with life and work at the ROG was the wife of the first Astronomer Royal, Margaret Flamsteed (c.1670-1730). She was the daughter of a London lawyer, Ralph Cooke and granddaughter of John Flamsteed's predecessor as rector of the Surrey parish of Burstow. She was probably baptised in Hackney in 1670 making her about 22 when she married the 46-year-old Astronomer Royal on 23 October 1692. Despite the age gap, there seems to have been a sincere attachment between the two, if the words 'beloved Wife' in Flamsteed's will and Margaret's determination to secure her husband's pothumous reputation are anything to go by.

The Royal Observatory from Crooms Hill, in about 1680 - the time that Margaret Flamsteed began living there.

Margaret Flamsteed was clearly a well-educated woman, both literate and numerate. We know from Flamsteed's records that she was occasionally of practical assistance during observational and calculating work, and manuscripts in the RGO archive in Cambridge record her study of mathematics and astronomy. These studies may have reflected those undertaken by Flamsteed's paid assistants and paying pupils - men and boys that Margaret would have taken care of as part of her general management of the household on Greenwich Hill. She seems to have been a particular asset when acting as hostess to the Observatory's visitors, no doubt smoothing over her husband's sometimes prickly temper.

It is, however, as Flamsteed's widow that Margaret is best remembered. Firstly she worked with the Observatory's former assistants to publish the full version of Flamsteed's book, Historia Coelestis, an abridged version of which had, to Flamsteed's fury, been published by Edmond Halley in 1712. Rather more sadly for us, she also removed and sold all of the astronomical and horological equipment that Flamsteed used at the Observatory. This she was probably justified in doing, as Flamsteed had either paid for the equipment himself or had received it as a personal gift from his patron Jonas Moore. It was to take several more Astronomers Royal before the questions of ownership and copyright that dogged the Flamsteeds were sorted out.

Continuing the theme of women connected to the ROG, this post leaps forward from Margaret Flamsteed in the 17th century to Annie Scott Dill Russell, in the 19th. Hired as a 'lady computer' at the ROG in 1891, Annie spent five years calculating and observing at Greenwich. In 1895 she then married E. Walter Maunder, the ROG First Assistant in charge of the Photographic and Spectroscopic Department. And, unusually for this period, marriage did not spell the end of her career in astronomy.

Annie was born in County Tyrone in 1868, and was educated at home and at the Ladies' Collegiate School in Belfast before gaining a scholarship to Girton College, Cambridge, and graduating with second-class honours in the mathematical tripos of 1889. She spent a year teaching mathematics before, in September 1891, she was hired to work at the ROG as one of the few female 'supernumerary computers' - those hired on a short-term basis rather than being permanent members of staff.

Usually computers were boys, arriving straight from local schools. But hiring women allowed William Christie, then Astronomer Royal, the luxury of gaining well-trained mathematicians at a cheap rate (they were paid about £4 a month, rising to £6 as 'soon as efficiency in the use of the Photographic Equatorial is acquired'). The experiment was something of a stop-gap, for Christie was in the process of persuading the Admiralty to increase the Observatory's (male) workforce. There may also have been a shortage of women prepared to accept the low wages: as Annie wrote, it 'is so small that I could scarcely live on it'.

Annie resigned her post in 1895, in preparation for marriage, although she did return to formal duties at Greenwich as a volunteer during the First World War. In between these periods she continued to pursue her interests in practical astronomy, receiving a small grant from Girton College to make a photographic study of the Milky Way. However, it was her husband's connection with Greenwich and her involvement with the British Astronomical Association that allowed Annie access to the equipment and resources needed for serious astronomical work.

She accompanied Walter on several eclipse expeditions and worked with him on the periodicity of sunspot activity, as well as publishing a number of books and papers under her own name or jointly with her husband. These included a catalogue of some 600 recurrent sunspot groups observed and photographed at Greenwich (1907), and The Heavens and their Story (1910). She was also editor of the BAA's journal for 15 years.

Annie Maunder (centre) preparing to observe the 1900 eclipse in Algiers with the British Astronomical Association (from E. Walter Maunder (ed.), The Total Solar Eclipse of May 1900).

In 1916 Annie became one of the first female fellows of the Royal Astronomical Society. She survived her husband by almost 20 years and late in life became an authority in ancient astronomies. Although she lived in Greenwich for at least 33 years, she later moved to Wandsworth, where she died in 1947.

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.

Back in April we met Annie Russell Maunder, but she was not, in fact, the first woman to be paid for her work at Greenwich under Astronomer Royal William Christie's new scheme. Russell's friend Alice Everett (1865-1949) had begun work as a supernumerary computer almost two years earlier, in January 1890.

Like Russell, Everett had attended Girton College, Cambridge and took the Mathematical Tripos, which essentially made both women as well-qualified as the Chief Assistant, Frank Dyson, who began work in 1894. Before this Everett had also attended Queen's College, Belfast, where she had taken first place in the first-year scholarship examination - causing the college authorities to question and decide against the eligibility of women in the competition.

At Greenwich, Everett was assigned to work in the Astrographic Department, contributing to the international Carte du Ciel project which aimed to map the skies using the still-new technique of stellar photography. Although her job-title was 'computer' (i.e. those who carried out routine calculations to 'reduce' raw observational data into usable tables), Everett was in fact trained to use the Observatory's new astrographic telescope in order to take the photographs, as well as then measuring the plates, calculating the co-ordinates of the stars and reducing the data for the catalogue. She also made observations for the Transit Department with the Prime-Meridian-defining Airy Transit Circle. Everett necessarily worked at the ROG at night, though we don't know whether she made her way through the park or stayed on-site when it was dark.


The Royal Observatory, Greenwich's astrographic telescope

Again like Russell, Everett was proposed but rejected for fellowship of the Royal Astronomical Society and instead found an outlet for her enthusiasm in the amateur British Astronomical Association, although she published in the Monthly Notices of the Royal Astronomical Society as well as in the BAA's journal, The Observatory and elsewhere.

After five years at Greenwich, Everett moved to the observatory in Potsdam, Europe's leading institution for astrophysical research, to continue work on the Carte du Ciel. This was only a temporary post, and after three years Everett was on the move again, this time for a year at the observatory of Vassar College. She failed to find another post in the USA and returned to London in 1900, where her interests turned to optics. She undertook a translation of a German optical text and carried out a number of experiments, but was unable to find regular paid work until the First World War, which gave many women an opportunity to enter the workforce. In 1917 she joined the staff of the National Physical Laboratory, where she remained until her retirement in 1925.

Even after retirement, Everett did not sit still. She took qualifications in electrical engineering and became involved with the Baird Television Company and Television Society, associations that were to last for the rest of her life. On her death in 1949 she left her library of scientific books to the Television Society.

For more information on and pictures of both these remarkable women, see Mary T. Brück, 'Alice Everett and Annie Russell Maunder torch bearing women astronomers'.

The Royal Observatory has several possible birthdays. I have, for example, seen it given as 4 March or 22 June 1675. The first is the date of Charles II's Royal Warrant that ordered the Board of Ordnance to pay for "the support and Maintenance" of John Flamsteed, appointed "our astronomical observator" and charged "to apply himself with the most exact care and diligence to the rectifying the tables of the motions of the heavens, and the places of the fixed stars, so as to find our the so much-desired longitude of places for the perfecting the art of navigation".

It should come as no surprise that a 17th-century astronomer was capable of drawing up an astrological chart. Although astronomy and astrology are now very different things, in the early modern period they were still closely allied. In this context it can be useful to think of astronomy as the observational practice that supplied data for a number of purposes, chiefly navigation, surveying, timekeeping and astrology. Flamsteed, like many other early modern astronomers, supplied his data to astrologers and evidently knew well how to cast and interpret a horoscope himself.