Sir David Gill FRS, the Scottish astronomer, was born on the 12th of June, 1843.
Sir David Gill was one of those scientists who is described as ‘the father of’ something; usually an ‘-ology’ or an ‘-ism’. In Gill’s case, he was the ‘father’ of astrography. Sir David Gill was a most remarkable astronomer, noted for his measurements of stellar parallaxes, and devoting a great deal of effort to establishing the distance between the Earth and the Sun; the so-called astronomical unit. His specialty was angular distance measurements and he made some of the worlds most accurate measurements before the space age. He was also a pioneer in the use of astrophotography (the use of photography in the preparation of star catalogs) and, as Astronomer Royal at the Cape of Good Hope, where much of his career was spent, he carried out several major geodetic surveys.
David Gill was born on the 12th of June, 1843, in Aberdeen, and at the age of fourteen, he joined Dollar Academy. The headmaster, Dr. Lindsay, encouraged his early interest in mathematics, natural philosophy and chemistry, and afterwards Gill spent two years in Marshall College, at the University of Aberdeen, as a private student. Gill’s father held a Royal Warrant as Watchmaker to Queen Victoria and, after leaving University, Gill joined his father in the watch making business, spending a year at Besacon, in Switzerland. During this time, of course, he acquired a feeling for precision instruments; a skill that was to be of great value.
In 1863, Gill returned to Aberdeen and started to become actively involved in Astronomy, a subject in which he had been interested from as young as the age of ten. In 1866, he built a small observatory, with a 12-inch telescope that he himself made. Later, in 1869, at a time when photography was still in its experimental stage, Gill took a picture of the Moon. That notable achievement drew attention to the young Scots amateur astronomer and set him off on the career that brought him international fame.
Gill’s photograph was truly excellent, considering the embryonic stage of the art and, in the following year of 1870, it came to the attention of Lord Lindsay of Dunecht. Lindsay was an aristocrat with enough money to build a private observatory, which was lavishly equipped with instruments finer than many of those available in Public Observatories. Lindsay offered Gill the post of Director of his observatory and “the rest is history” as they say.
At the Dunecht Observatory, Gill made some of the most accurate measurements of angular distances to stars using a 4-inch heliometer, an instrument that he later privately acquired from Lord Lindsay. Gill’s innate skill in the use of precision instruments, which had been honed during his watchmaking days in Switzerland, came to the fore. The results he obtained using this instrument, remained amongst the best ever obtained up until the era of space probes and computer technology.
In 1874, Gill went to Mauritius with Lord Lindsay in order to observe the transit of Venus. That was a privately sponsored expedition with Gill as Chief Observer. The results were disappointing, however, Gill later became leader of a successful attempt (in 1882). He next joined the Royal Astronomical Society’s sponsored expedition to the Ascension Islands, in 1877. That was where he first observed the opposition of Mars and calculated a very accurate result for the distance between the Sun and the Earth. Amazingly, the value that Gill calculated back then was within 0.2 per cent of the accepted contemporary value.
With the recommendation of Lord Lindsay, Gill was appointed Her Majesty’s Royal Astronomer and Director of the Observatory at the Cape of Good Hope, in 1879. On his appointment, the place was a bit run down and outdated, but by the time he retired, the Cape Observatory was one of the finest and best equipped observatories in the world. Soon after Gill arrived in Cape Town, he used the Repsold Heliometer to measure the distances to a number of minor planets. The parallax value of 8".80 that he used was employed in the computation of all almanacs until 1968, when radar echo methods and data from the Mariner Probe refined the value – ever so slightly – to 8".794.
When the Great Comet appeared, in 1883, Gill remembered his moon photograph and got the local photographer to fix his camera to the clock driven equatorial telescope. Together, they took several astounding photographs, which showed not only the comet, but the also the background stars, with absolute clarity and sharpness. Gill sent the results to the Royal Astronomical Society and the Paris Observatory. He then ordered a larger lens and embarked upon the most ambitious project of his career. This was ‘The Cape Photographic Durchmusterung for the Equinox 1875’, which extended Argelander’s ‘Bonn Durchmusterung’ to the South Pole. The finished catalogue gave the brightness and approximate positions of nearly half a million stars in the Southern Hemisphere.
In recognition of Gill’s status as the ‘father of astrography’ the Paris Observatory engaged him as an important contributor to its ambitious ‘Carte du del’ project, which set out to create a photographic chart of the entire sky. Its goal was to produce a catalogue giving the precise positions of more than a million stars down to the eleventh magnitude. A fine new telescope, the astrographic refractor, was acquired for the Cape Observatory, but the overambitious project wasn’t completed until long after Gill was dead.
Amongst the awards and recognition Gill gained was ‘Commandeur de la Legion d'Honneur’, from France, the German ‘Order Pour le Merite for Arts and Sciences’, the ‘James Craig Watson Medal’, from the National Academy of Sciences, and the ‘Bruce Medal’. The ‘Gill Award’, South Africa’s highest award in the field of Astronomy, takes his name. There is a planet (#11761) called Davidgill and there is a Gill Crater on the Moon and on Mars. Gill was knighted in 1900 and, in 1906, due to ill health, he and his wife retired to Kensington, in London. Sir David Gill died in London on the 24th of January, 1914, and was taken to his home City of Aberdeen, where he was buried.