Wadhurst Astronomical Society Newsletter January 2021
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Wadhurst Astronomical Society Newsletter January 2021 Welcome to the New Year and the January edition of the Wadhurst Astronomy Society newsletter. How many Zoom meetings before we can meet again in person? But first we look at last month’s meeting; our Christmas Zoom meeting. We learnt about the observatory at Greenwich, how it came into being, of its importance to navigation and then we learnt about the Astronomers Royal. John Wayte presided over another of his popular Christmas Quizzes, which was great fun and included some questions to amuse and challenge our knowledge of astronomy. Towards the end of the newsletter, Brian Mills provides his detailed Sky Notes for January, and finally there is a bit of sad news about the loss of a distinguished observatory. THE DECEMBER ZOOM MEETING Phil Berry opened the December Zoom meeting and after outlining the evening’s programme he introduced our own Chairman, Brian Mills to give the Christmas talk but before Brian began, he said it had been decided by the Committee that owing to the pandemic, the Society had been unable to hold any actual meetings at Uplands Community College since March and therefore anyone who paid their subscription any time during 2020 will automatically remain a paid up member of the Society for the year 2021. Greenwich and the Astronomers Royal Brian Mills FRAS At the start of his talk, Brian posed the question, why was the observatory built. In the 17th century Britain, as an island nation was dependent for trade and contact with its colonial outposts solely by sea. We were reminded of the many disasters that occurred at sea with the loss of ships, their crews and their cargo because in those day, maps were not very accurate and sea captains had no real way of knowing exactly where on these maps they were. So, it was necessary to acquire a way of knowing their positions much more accurately. It had been suggested that the position of the Moon as it moved in front of the background fixed stars could be one method of finding longitude at sea. The essential thing was that the position of the Moon and stars would need to be known much more precisely. With this in mind an approach was made to King Charles the Second and work was begun to build the observatory at Greenwich overlooking the Queen’s House and the Thames. The location for the new observatory was on the site of the old Duke of Humphrey’s Tower which had become a ruin. The observatory was built by Christopher Wren and finished in 1675. The new observatory at Greenwich to the left, overlooking the Queen’s House and the River Thames Image: Engraving by S Wellcome/Creative Common licence 1 Brian said that the Royal Society were already planning an observatory at Chelsea with John Flamsteed as observer, so it followed that Charles II appointed Flamsteed as the observer at the new Greenwich observatory. Originally, the building was intended for navigation purposes and not as an observatory and since the original foundations were used, it faced onto the Queen’s House, which meant that it was not in line with the meridian but was 13o off to one side. Early observing was done from the flat roof of the new building using a 16-foot-long telescope which was later replaced with a 27- foot telescope. A 60-foot telescope was also used in the grounds of the observatory. Flamsteed did the observing himself and with help, built the instruments he used, although at the time he wasn’t called Astronomer Royal but Astronomical Observator. We were told that that title wasn’t assumed until Neville Maskelyne adopted the title himself in 1765. The Astronomer Royal was responsible for everything including his budget until 1965 when the Science and Research Council was formed and took over responsibility for the Royal Greenwich Observatory, the Royal Observatory in Edinburgh, the Appleton Laboratory and the Rutherford High Energy Laboratory. Brian said that in 1971, Richard Wooley was still in the post of Astronomer Royal but it was announced that when he retired, the new director would not necessarily be the Astronomer Royal and Margaret Burbage became Director of the Royal Greenwich Observatory, with Martin Ryle becoming Astronomer Royal, a title that became a purely honorary one. The Astronomer Royal has always been a member of the Royal Household, answerable to the Lord Chamberlain and must be available to the Monarch to answer questions on astronomy and science, all for a stipend of just £100 a year. The first person to take on the role of Astronomer Royal was John Flamsteed from 1675. His assistant built the mural arc with which he and Flamsteed made 28,000 observations of star positions. At the time, Isaac Newton was perfecting his calculations on the motion of the Moon and needed precise data which Flamsteed already had and was continuing to obtain. But Flamsteed regarded the data as his personal property and there was conflict between the two with the result that they became hostile to each other. Somehow the Royal Society managed to get hold of a copy of Flamsteed’s work and 400 copies appeared in 1712 against Flamsteed’s wishes. He manages to get hold of 300 of them and burnt them in Greenwich Park. John Flamsteed suffered from ill health towards the end of his life and died in 1719 at the age of 73. His widow and assistants completed his “Historia Coelestis” Britannic in 1725 and his “Atlas Coelestis” in 1729. We were told that his widow removed all the equipment from the observatory as directed in Flamsteed’s will. John Flamsteed, the first Astronomer Royal Edmond Halley, the Second Astronomer Royal Image: Portrait by Godfrey Kneller/ Wellcome Library Image: Portrait by R Philips Brian said that by comparison, the second Astronomer Royal, Edmond Halley, was by all accounts a far more agreeable man. 2 Halley was born in Hackney to a rich family in 1656. He went to Queen’s College in Oxford where he met Flamsteed but left his studies at Oxford to travel to St Helena and record the southern stars to complement Flamsteed’s work. Although he only managed to record 341 star positions, the results were published in 1678 in his “Catalogue of the Southern Stars”. When trying to explain Kepler’s three laws of planetary motion from his observations, Halley couldn’t manage ellipses so contacted Isaac Newton who said he had already worked it out and eventually Halley paid for Newton’s work on the results to be printed as Newton’s “Principia”. In 1703 Halley became professor of Geometry at Oxford despite Flamsteed’s objections. We were then told that Halley eventually took on the role of Astronomer Royal at Greenwich Observatory in 1720, having to replace the equipment removed by Flamsteed’s widow. One of his tasks was to follow and measure the precise position of the Moon over one entire Saros cycle which Brian described as the time between the Earth, Moon and Sun being in line and returning to almost exactly the same geometric positions, taking 18 years, 11 days and 8 hours. The purpose was to allow more accurate lunar tables to be calculated and so more accurate longitude measurements to be recorded. Halley was quite elderly when he took over the post and died from a stroke, dying five years later in 1742 aged 85. But he was able to predict that the comet of 1682 would reappear in 1758 and finally the comet would be named after him. The next Astronomer Royal was James Bradley, also educated at Oxford. Whilst at Oxford he became professor of astronomy and discovered the Aberration of Light which produces an apparent motion a celestial object to be displaced towards the direction of the observer’s motion. Brian said that from this it showed finally that the Earth was not at the centre of the Universe and that the Earth was in fact orbiting the Sun. Bradley was Astronomer Royal from 1742 to 1762 and during his time managed to improve on previous levels of accuracy of observations and also showed the nutation of the Earth. Precession taking 26,000 years was already known but these small fluctuations, taking just 8.6 years, became apparent because of Bradley’s accuracy in observations. Brian said this nutation is caused by the gravitational effects of the Sun and Moon through the Earth’s equatorial bulge. Nathaniel Bliss became the next Astronomer Royal in 1762 and remained in office until only 1764 but we were told he contributed very little to astronomy. Brian then briefly covered the following Astronomer Royals beginning with Nevil Maskelyne in the role from 1765 until 1811. During his tenure he was a great critic of John Harrison who made more and more accurate clocks to be carried on board ships to improve the measure of longitude of the vessels as they travelled at sea. Maskelyne’s concern was in how the Board of Longitude was spending public money. Maskelyne attempted to measure the mass of the Earth by using an almost conical shaped mountain in Scotland and multiplied it up to try and calculate the density of the Earth. The next Astronomer Royal was John Pond from 1811 until 1835. It was Pond that was responsible for the installation of the Time Ball on the observatory roof in 1883, so that when it was released and fell at one-clock, ships in the Pool of London could see it and set their clocks.