 When Ceres has an opposition near the perihelion , it can reach a visual magnitude of + 6 @.@ 7 . This is generally regarded as too dim to be seen with the naked eye , but under exceptional viewing conditions a very sharp @-@ sighted person may be able to see it . Ceres was at its brightest ( 6 @.@ 73 ) on 18 December 2012 . The only other asteroids that can reach a similarly bright magnitude are 4 Vesta , and , during rare <unk> near perihelion , 2 Pallas and 7 <unk> . At a conjunction Ceres has a magnitude of around + 9 @.@ 3 , which corresponds to the faintest objects visible with 10 × 50 <unk> . It can thus be seen with <unk> whenever it is above the horizon of a fully dark sky . 
