#OTD in 1862.
Alvan Graham Clark discovers the white dwarf star Sirius B, a companion of Sirius, through an 18.5-inch (47 cm) telescope now located at Northwestern University.
This discovery of Sirius B, or affectionately "the Pup", proved an earlier hypotheses (Friedrich Wilhelm Bessel in 1844) that Sirius, the brightest star in the night sky with an apparent magnitude of −1.46, had an unseen companion disturbing its motion.
