Minor planets. I. The rotation of Vesta

A set of 13 light curves for 4 Vesta was obtained between November 1958 and May 1959. The set is compared with light curves observed in 1950 (by H. L. Johnson), in 1952 (D. L. Harris), in 1954 (L. Bin- nendijk), and in 1967 (this paper). The speed as well as the sense of rotation are derived from the effect of aspect change on the apparent rotational period ("photometric astrometry"). The rotation is direct, the true period is 5h20 31.665 (+0.003 p.e.), and the ecliptic longitude and latitude of the north pole are 126 (+5 ) and +65 (+4 ). Vesta differs from the other asteroids in that its light curve has only one maximum and one minimum, indicating a nearly spherical shape for Vesta with a darker, and slightly bluer, region on one side. The brightness-phase function shows a nonlinear increase near opposition ("opposition effect"). The colors B - V and U - B increase with the orbital phase angle ("reddening with phase").