Observations of the Great Comet of 1680 by Cassini, 1681. Page from 'Abrege des observations' (1681) by Italian astronomer Giovanni Domenico Cassini (1625-1712). This work contained his observations of the Great Comet of 1680, with this page showing theoretical calculations relating to the orbit of the comet. This comet was the first discovered by telescope. It was one of the brightest comets of the 17th century, reaching peak brightness on 29 December 1680, remaining visible until March 1681. It has the modern designation C/1680 V1, and is also known as Kirch's Comet after its discoverer. It is sometimes called Newton's Comet as the orbital data was used by Newton to verify Kepler's laws of motion.