The correspondence is chiefly with other astronomers in the United States and deals with astronomy in general including Pettit's work at Mount Wilson, telescopes and ultraviolet light research. The rest of the collection is made up of manuscripts, notes, notebooks and printed items. The majority of the manuscripts are by Edison Pettit (two are co-written with Seth Barnes Nicholson and there is one abstract by Harold D. Babcock). The manuscripts deal with astronomy including thermocouples, Pettit's ultraviolet research, the Sun, the Moon and telescope lenses. One notable manuscript is a rather lengthy typed manuscript with handwritten edits (facsimile copy) regarding the moon and which is probably written by Edison Pettit (but never published?). There are also miscellaneous notes related to astronomy in general and more specifically the moon and nebulae including galley proofs for the book Physics and astronomy of the Moon, edited by Zden k Kopal. The twelve Nebular Photometry notebooks in boxes 8 and 9 were kept by Pettit while at work observing the sky. There are also three reprints of articles (one by Pettit). The albums in box 10 include one with photographs (nebulae) but the other three contain handwritten notes and lists kept by Pettit. The collection has several photographs scattered throughout the collection.