Lexell Comet

a bright comet discovered by the French astronomer C. Messier in 1770. It was the first known short-period comet and was named in honor of A. J. Lexell (A. I. Leksel’), who calculated its orbit. The considerable variations in its orbit during close approaches to Jupiter in 1767 and 1779 explain why the Lexell comet was not observed before or after 1770. Since the comet’s close approach to the earth in 1770 did not cause noticeable variations in the earth’s motion, P. Laplace concluded that the comet’s mass was less than 1/5,000 the mass of the earth.