In 1849 Petersen found the open cluster NGC 2194 in Orion with the 7" Repsold refractor at Altona Observatory (near Hamburg). However, the very discoverer is W. Herschel.
| D | N | NI | Y | Ap | I | T | Discoverer | Observer | Con | Type | S | Author | Title | Source |
| N | 2194 | 1849 | 7,0 | Rr | v | Herschel W. 11.2.1784 | d'Arrest 18.9.1862 | ORI | III1r | 4 | Petersen, A. C. | Letter from Dr. A. C. Petersen of the Altona Observatory to the editor | AJ 1, 47-48 (1850) |