RT @NASAhistory: #OTD in 1862, American astronomer Alvan Graham Clark 1st observed the white dwarf companion of Sirius. https://t.co/t86X7T3yS9
RT @NASAhistory: #OTD in 1862, American astronomer Alvan Graham Clark 1st observed the white dwarf companion of Sirius. https://t.co/t86X7T3yS9