page_title: George Biddell Airy
section_title: Astronomer Royal
hierarchical_section_title: George Biddell Airy / Biography / Research / Astronomer Royal
caption_attribution_description: The Airy Transit Circle was designed by George Biddell Airy, and came into use 150 years ago. The first observation was taken on 4 January 1851, three days later than Airy had intended due to the English weather. The circle remained in continual use until 1938, and the last ever observation was taken in 1954. Mounted in the Transit Circle Room,defining the Greenwich Meridian since 4 January 1851.Makers: Ransomes &amp; May of Ipswich (engineering)Troughton &amp; Simms of London (optical and instrumental)to the design of G. B. Airy. Lens: 8.1 inch aperture objective glass Focal Length: 11 feet 7 inches Magnification: 195 (180 for the Sun).
context_page_description: Sir George Biddell Airy KCB PRS was an English mathematician and astronomer, Astronomer Royal from 1835 to 1881. His many achievements include work on planetary orbits, measuring the mean density of the Earth, a method of solution of two-dimensional problems in solid mechanics and, in his role as Astronomer Royal, establishing Greenwich as the location of the prime meridian. His reputation has been tarnished by allegations that, through his inaction, Britain lost the opportunity of priority in the discovery of Neptune.
context_section_description: In June 1835 Airy was appointed Astronomer Royal in succession to John Pond, and began his long career at the national observatory which constitutes his chief title to fame. The condition of the observatory at the time of his appointment was such that Lord Auckland, the first Lord of the Admiralty, considered that "it ought to be cleared out," while Airy admitted that "it was in a queer state." With his usual energy he set to work at once to reorganise the whole management. He remodelled the volumes of observations, put the library on a proper footing, mounted the new (Sheepshanks) equatorial and organised a new magnetic observatory. In 1847 an altazimuth was erected, designed by Airy to enable observations of the moon to be made not only on the meridian, but whenever it might be visible. In 1848 Airy invented the reflex zenith tube to replace the zenith sector previously employed. At the end of 1850 the great transit circle of 203 mm (8 inch) aperture and 3.5 m (11 ft 6 in) focal length was erected, and is still the principal instrument of its class at the observatory. The mounting in 1859 of an equatorial of 330 mm (13 inch) aperture evoked the comment in his journal for that year, "There is not now a single person employed or instrument used in the observatory which was there in Mr Pond's time"; and the transformation was completed by the inauguration of spectroscopic work in 1868 and of the photographic registration of sunspots in 1873.
  The formidable undertaking of reducing the accumulated planetary observations made at Greenwich from 1750 to 1830 was already in progress under Airy's supervision when he became Astronomer Royal. Shortly afterwards he undertook the further laborious task of reducing the enormous mass of observations of the moon made at Greenwich during the same period under the direction, successively, of James Bradley, Nathaniel Bliss, Nevil Maskelyne and John Pond, to defray the expense of which a large sum of money was allotted by the Treasury. As a result, no fewer than 8,000 lunar observations were rescued from oblivion, and were, in 1846, placed at the disposal of astronomers in such a form that they could be used directly for comparison with the theory and for the improvement of the tables of the moon's motion.
  For this work Airy received in 1848 a testimonial from the Royal Astronomical Society, and it at once led to the discovery by Peter Andreas Hansen of two new inequalities in the moon's motion. After completing these reductions, Airy made inquiries, before engaging in any theoretical investigation in connection with them, whether any other mathematician was pursuing the subject, and learning that Hansen had taken it in hand under the patronage of the king of Denmark, but that, owing to the death of the king and the consequent lack of funds, there was danger of his being compelled to abandon it, he applied to the admiralty on Hansen's behalf for the necessary sum. His request was immediately granted, and thus it came about that Hansen's famous Tables de la Lune were dedicated to La Haute Amirauté de sa Majesté la Reine de la Grande Bretagne et d'Irlande.
  In 1851 Airy established a new Prime Meridian at Greenwich. This line, the fourth "Greenwich Meridian", became the definitive internationally recognised line in 1884.
caption: Airy's Transit Circle in the Transit Circle Room, Greenwich
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