Airy's Transit Circle: observation and reduction ledgers and associated papers

The Airy Transit Circle was installed under the direction of George Airy to supersede the separate transit instruments and the mural circles still in use in the 1850s. The new instrument allowed the observer to obtain measurements of both right ascension and declination of a celestial object on the same meridian transit. The purpose of these observations was the production of raw data for the compilation of the star catalogues. The Airy Transit Circle was in operation from 1851 to 1954 although much work done began to be done on alternative instruments from 1920-30s. The principal one of these was the Cooke Reversible Transit Circle which was dismantled and reinstalled to continue work at Herstmonceux whilst the Airy Transit circle remained as museum piece at Greenwich. It appears the CRTRC was being used consistently from 1936 and the Airy TC was last used regularly in 1954. Detailed information about the construction of the transit circles and process of making the observations may be found in ''Greenwich Observatory: Volume 3: The Buildings and Instruments'' (Taylor and Francis; London, 1975).

The items in this collection are both bound and unbound sets of the pre-printed forms which were used to record measurements of the transits of objects across the Greenwich Meridian and thus allow the accurate calculation of their position. Observations made on the Airy and Cooke Reversible Transit Circles were treated by the observers as a continuous sequence and the forms in later volumes are generally headed "Cooke Reversible Transit Circle".

Produced or accumulated by the Royal Observatory, Greenwich and the Royal Greenwich Observatory.

N.B. Some volumes series /1 and series /4 should be ordered 48 hours in advance due to their poor physical condition. Please see individual entries for details.

Please cite as Royal Greenwich Observatory Archives, Airy's Transit Circle: observation and reduction ledgers and associated papers, RGO 126

Further records relating to the Airy Transit circle in the RGO collection include: RGO 6/793, an observing log for 1874/5; in RGO 9/1 some early twentieth century correspondence; and some papers on the use of the Airy Transit Circle, 1940-60s. Other RGO observational records may be found under classmarks bearing the titles of relevant departments, projects or instruments. Of these RGO 164: Cooke Reversible Transit Circle: observations and records may be of particular interest.

The online catalogue for Janus was compiled from an existing list in 2008-9 by Zoe A. Rees, Department of Manuscripts and University Archives.