January 31: Telescope maker Alvin Clark discovers dwarf companion of Sirius.

May 27: Astronomer John Campbell born in Lisburn, Co Antrim, Ireland.

May 31: Information obtained from Thadeus S. C. Lowe’s balloon observation saves Union forces from defeat at the Battle of Fair Oaks, Virginia during the U. S. Civil War. Union General George McClellan is warned by Lowe of Confederate General Albert Johnston’s approaching troops.