A rotational lightcurve for this asteroid was obtained from photometric observations made at the Australian Oakley Southern Sky Observatory (E09) in September 2014. The lightcurve gave a rotation period of 7.823±0.005 hours with a brightness variation of 0.50 in magnitude (U=3-).
Diameter and albedo
According to the 2015/16 NEOWISE mission results of NASA's space-based Wide-field Infrared Survey Explorer,
Geisei measures 5.21 and 5.23 kilometers in diameter and its surface has an albedo of 0.34 and 0.38, respectively. Preliminary WISE results gave a diameter of 6.582 kilometers and an albedo of 0.275.
The Collaborative Asteroid Lightcurve Link assumes an albedo of 0.24 – derived from 8 Flora, the largest member and namesake of the Flora family – and calculates a diameter of 6.81 kilometers using an absolute magnitude of 13.0.
This minor planet is named after the small Japanese village of Geisei, where the discovering observatory is located. Geisei is situated near the city of Kōchi, after which Tsutomu Seki's first discovery, the asteroid 2396 Kochi, is named. The approved naming citation was published by the Minor Planet Center on 6 June 1982 (M.P.C. 6956).