3133 Sendai

3133 Sendai, provisional designation, is a stony Flora asteroid from the inner regions of the asteroid belt, approximately 8 kilometers in diameter. It was discovered on 4 October 1907, by German astronomer August Kopff at Heidelberg Observatory in southwest Germany. The asteroid was named for the Japanese city of Sendai.

Orbit and classification
Sendai is a member of the Flora family, one of the largest groups of stony asteroids in the main-belt. It orbits the Sun in the inner main-belt at a distance of 1.8–2.5 AU once every 3 years and 3 months (1,176 days). Its orbit has an eccentricity of 0.16 and an inclination of 7° with respect to the ecliptic.

Physical characteristics
Sendai has been characterized as a stony S-type asteroid.

Diameter and albedo
According to the surveys carried out by NASA's Wide-field Infrared Survey Explorer and its extended NEOWISE mission, the asteroid's surface has an albedo of 0.21 and 0.31, with a diameter of 8.3 and 7.3 kilometers, respectively. The Collaborative Asteroid Lightcurve Link assumes an intermediate albedo of 0.24 – which derives from 8 Flora, the largest member and namesake of this orbital family – and calculates a concurring diameter of 7.5 kilometers.

Lightcurves
In 2010, two rotational lightcurves were obtained by amateur astronomer Ralph Megna at Goat Mountain Astronomical Research Station (G79), and by the U.S. Palomar Transient Factory in California. The concurring lightcurves showed a rotation period of $7.25$ and $8.323$ hours, respectively (U=3-/2).

Naming
This minor planet was named for the second largest city north of Tokyo, Sendai (pop. 1 million), location of the Tōhoku University. It is the home of the Sendai Astronomical Observatory, which was founded in 1955, on appeal by the Sendai Amateur Astronomical Association. The observatory has discovered several minor planets. The official naming citation was published by the Minor Planet Center on 29 September 1985 (M.P.C. 10045).