MLA

Kepler, Johannes, 1571-1630. De cometis libelli tres : I. Astronomicvs, theoremata continens de motu cometarum ubi demonstratio apparentiarum & altitudinis cometarum qui annis 1607. & 1618. conspecti sunt, ... : II. Physicvs, continens physiologiam comentarum nouam ... : III. Astrolo. 1619, [i.e. 1620]. https://collections.library.yale.edu/catalog/2041908.

APA, 6th edition

Kepler, Johannes, 1571-1630. (1619, [i.e. 1620])[De cometis libelli tres : I. Astronomicvs, theoremata continens de motu cometarum ubi demonstratio apparentiarum & altitudinis cometarum qui annis 1607. & 1618. conspecti sunt, ... : II. Physicvs, continens physiologiam comentarum nouam ... : III. Astrolo]. https://collections.library.yale.edu/catalog/2041908.