Four-color photometry of the Galilean satellites

Photometry obtained in 1973 on the uvby system yields high-precision rotational light curves for Io, Europa, and Ganymede at a mean phase angle of about 6 deg. By combining our observations with photometry obtained by others over a broader range of phase angle, we also derive improved values for the phase coefficients and opposition surges of the four Galilean satellites. The values of V(1, 0) obtained by linear extrapolation to zero phase are accurate to + or - 0.03 magnitudes. We also derive the colors of the sun on the uvby system and use these to obtain albedos of the satellites in four colors.