91 Aegina (from Latin Aegīna, Aegīnēta) is a large main-belt asteroid. It was discovered by French astronomer Édouard Jean-Marie Stephan on 4 November 1866. It was his second and final asteroid discovery. The first was 89 Julia. The asteroid's name comes from Aegina, a Greek mythological figure associated with the island of the same name.

This body is orbiting the Sun with a period of 4.17 years and an eccentricity of 0.105. The orbit of this object brings it to within of the dwarf planet Ceres, and the resulting gravitational interaction has been used to produce mass estimates of the latter.

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