The Airy Transit Circle, installed in 1850 and first used on 4th January 1851 is emblematic of the revolution in working practice introduced by Airy at the Royal Observatory. It sits on the north-south line, which today marks longitude 0°. This Prime Meridian, signals the start of the Universal day for the entire world. At the time of its installation, the Airy Transit Circle marked a huge advance on existing technology. A transit instrument is always lined up with a north-south line, or meridian. When a star passes over the meridian, the transit instrument can be used to measure the angle at which this happens. Read more
The Airy Transit Circle was designed by George Biddell Airy, and came into use 160 years ago. The first observation was taken on 4 January 1851, three days later than George 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. Read more