John Goodricke (1764-1786)
Autograph letter signed (‘J Goodricke’) to Nathaniel Pigott, 'M. Yard' [York], 18 December n.y.
Two pages, 159 x 200mm, bifolium. Provenance: Sotheby's, 24 July 1978, lot 233.

Sending instructions to a fellow astronomer on observing Uranus through a telescope: ‘I believe you will see a star of the 6^th May very bright which when you see, you must take as the Georgium Sidus and accordingly observe it’. The present letter details the exact timings and position of Georgium Sidus [Uranus] in the night sky, giving precise instructions to locate it: ‘I now take this opportunity to send you the Right Ascensions of the Georg. Sidus in sidereal time’. Advising Pigott to ‘move the telescope up & down one degree above 60° [...] If you observe it twice, you can be sure whether it is the planet by its motion, which I believe is sensible in a day or two [...] I will look for the relative position of the planet amongst the small star near it’. Goodricke concludes by wishing Pigott success in his viewing.

Georgium Sidus was originally discovered by William Herschel in 1781: it was later renamed Uranus.