1552 Bessel

1552 Bessel, provisional designation, is a stony Eoan asteroid from the outer regions of the asteroid belt, approximately 18 kilometers in diameter. It was discovered on 24 February 1938, by Finnish astronomer Yrjö Väisälä at Turku Observatory in Southwest Finland, and named after German astronomer Friedrich Bessel.

Orbit and classification
Bessel is a stony asteroid and a member of the Eos family that orbits the Sun in the outer main-belt at a distance of 2.7–3.3 AU once every 5 years and 3 months (1,909 days). Its orbit has an eccentricity of 0.10 and an inclination of 10° with respect to the ecliptic. First observed as at Heidelberg in 1933, the body's observation arc begins at Turku, 5 days prior to its official discovery observation.

Naming
This minor planet was named after German astronomer Friedrich Wilhelm Bessel (1789–1846), who measured the first stellar parallax in 1838. His measured parallax of 0.314 arcseconds for 61 Cygni gave a distance of 10.3 light-years, which is 9.6% off today's measured distance of 11.4 light-years. Bessel is also honored by the lunar crater Bessel. The official was published by the Minor Planet Center on 30 January 1964 (M.P.C. 2278).

Rotation period and pole
In March 2011, a rotational lightcurve of Bessel was obtained from photometric observations by Italian amateur astronomer Silvano Casulli. Lightcurve analysis gave a well-defined rotation period of 8.996 hours with a brightness variation of 0.29 magnitude (U=3).

In 2016, a modeled lightcurve using photometric data from various sources gave a concurring period of 8.96318 hours, as well as a spin axis of (61.0°, −50.0°) in ecliptic coordinates (λ, β).

Diameter and albedo
According to the survey carried out by NASA's Wide-field Infrared Survey Explorer with its subsequent NEOWISE mission, Bessel measures between 16.63 and 18.817 kilometers in diameter, and its surface has an albedo between 0.1514 and 0.193. The Collaborative Asteroid Lightcurve Link derives an albedo of 0.1448 and a diameter of 18.33 kilometers with an absolute magnitude of 11.4.