309 Fraternitas is a typical Main belt asteroid. It was discovered by Johann Palisa on 6 April 1891 in Vienna. The asteroid name is Latin for 'fraternity'; it was so named in order to commemorate the 25th anniversary of the Maturitätsprüfung Fraternity.

This minor planet is orbiting the Sun at a distance of 2.665 AU with an orbital eccentricity (ovalness) of 0.115 and a period of 4.35 yr. The orbital plane is inclined at an angle of 3.72° of the ecliptic. Analysis of the asymmetric bimodal light curve of the asteroid from photometric data collected during 2014 provide a rotation period of 22.398±0.001 h with a brightness variation of 0.12±0.01 in magnitude.

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