1535 Päijänne

1535 Päijänne, provisional designation , is an asteroid from the outer region of the asteroid belt, approximately 25 kilometers in diameter. It was discovered on 9 September 1939, by Finnish astronomer Yrjö Väisälä at the Turku Observatory in Southwest Finland. It was later named for Lake Päijänne.

Orbit
Päijänne orbits the Sun in the outer main-belt at a distance of 2.6–3.8 AU once every 5 years and 8 months (2,057 days). Its orbit has an eccentricity of 0.19 and an inclination of 6° with respect to the ecliptic. It was first identified as at Simeiz Observatory in 1916. The body's observation arc begins 6 years prior to its official discovery with its identification as at Heidelberg Observatory.

Physical characteristics
Päijänne is classified as both S-type and transitional CX-type asteroid.

Lightcurves
In September 2006, a rotational lightcurve of Päijänne was obtained from photometric observations taken by French amateur astronomer Laurent Bernasconi. The lightcurve analysis gave a well-defined rotation period of 8.8448 hours with a change in brightness of 0.50 magnitude (U=3).

Diameter and albedo
According to the surveys carried out by the Infrared Astronomical Satellite IRAS, the Japanese Akari satellite, and NASA's Wide-field Infrared Survey Explorer with its subsequent NEOWISE mission, Päijänne measures between 23.836 and 26.72 kilometers in diameter, and its surface has an albedo between 0.1299 and 0.164. The Collaborative Asteroid Lightcurve Link derives an albedo of 0.0638 and a diameter of 26.36 kilometers with an absolute magnitude of 11.5.

Naming
This minor planet was named for Finland's second largest lake, Päijänne, located in south-central Finland, and more than a thousand square kilometers in size. The official was published by the Minor Planet Center on 20 February 1976 (M.P.C. 3929).