But during rare oppositions , every 81 years , such as in 1975 and 2056 , Eros can reach a magnitude of +7.1 , which is brighter than Neptune and brighter than any main belt asteroid except 4 Vesta and , not usually , 2 Pallas and 7 Iris . During rare oppositions , every 81 years , such as in 1975 and 2056 , Eros can reach a magnitude of +7.0 , which is brighter than Neptune and brighter than any main-belt asteroid except 4 Vesta and , rarely , 2 Pallas and 7 Iris .