American astronomer (1906–1997) best known for discovering Pluto in 1930. ALS, one page, 8.5 x 11, New Mexico State University letterhead, March 1, 1991. Letter to Dr. Adam Langweiler, in part: "Yes, I was surprised and delighted when Dr. Christy found Charon, because it would yield a reliable determination of its mass—shockingly small (1/400th Earth, 1/6th our moon). During the last 3 years the plane of Charon's orbit was edgewise to our view, resulting in Charon passing in front of and behind Pluto. The changes in brightness and duration resulted in accurate determination of their sizes. The discovery of the super-cluster of galaxies in the fall of 1936, aroused the most interest." In fine condition. Charon is the largest of the five known natural satellites of the dwarf planet Pluto.Format: ALS