3915 Fukushima

3915 Fukushima, provisional designation, is a carbonaceous asteroid from the inner regions of the asteroid belt, approximately 21 kilometers in diameter.

It was discovered on 15 August 1988, by Japanese astronomers Masayuki Yanai and Kazuro Watanabe at the Kitami Observatory in eastern Hokkaido, Japan, and named after amateur astronomer Hisao Fukushima.

Orbit and classification
Fukushima orbits the Sun in the inner main-belt at a distance of 2.3–2.5 AU once every 3 years and 10 months (1,392 days). Its orbit has an eccentricity of 0.04 and an inclination of 14° with respect to the ecliptic. The asteroid was first identified as at Heidelberg Observatory in 1926, extending the body's observation arc by 62 years prior to its official discovery observation at Kitami.

Physical characteristics
Fukushima has been characterized as a reddish P-type asteroid by the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer. It is also an assumed C-type asteroid.

Rotation period
Several high-quality rotational lightcurves were obtained from photometric observations since 2003. An observation by Brian D. Warner at the U.S. Palmer Divide Observatory in Colorado rendered a rotation period of $20.38$ hours with a high brightness variation of 0.67 in magnitude (U=3), indicating that the body has a non-spherical shape. This observation concurs with another measurement taken at the Oakley Observatory that rendered a period of $21.993$ and an amplitude of 0.50 mag (U=3), superseding a less accurate lightcurve produced by the PDS of 8.40 hours (U=2). In 2011, an observation by René Roy gave another concurring period of $22.354$ hours and an amplitude of 0.79 mag (U=3). On 16 December 2012, the asteroid occulted the star HIP 4315 over parts of Europe and North America. At the time the body's brightness was 16.3 in magnitude (mag) and that of the star was 8.5 mag.

Diameter and albedo
According to the space-based surveys carried out by the Infrared Astronomical Satellite IRAS, the Japanese Akari satellite, and the NEOWISE mission, the asteroid has a low albedo in the range of 0.044 and 0.056 with a diameter between 20.3 and 22.8 kilometers. The Collaborative Asteroid Lightcurve Link gives preference to the results obtained by IRAS with an albedo of 0.0561 and a diameter of 20.38 kilometers.

Naming
This minor planet was named in honor of Japanese researcher and amateur astronomer, Hisao Fukushima (1910–1997), known for his research in hydrodynamics. He was professor emeritus at Hokkaido University, and, as an active amateur astronomer, a member of the Hokkaido Astronomical Liaison Group. The approved naming citation was published by the Minor Planet Center on 23 December 1988 (M.P.C. 14030).