783 Nora

783 Nora (prov. designation: or ) is a dark background asteroid from the inner regions of the asteroid belt. It was discovered by Austrian astronomer Johann Palisa at the Vienna Observatory on 18 March 1914. The carbonaceous C-type asteroid has a longer-than average rotation period of 55.5 hours and measures approximately 40 km in diameter. It was likely named after Nora Helmer, principal character in the play A Doll's House by Norwegian poet Henrik Ibsen.

Orbit and classification
Nora is a non-family asteroid of the main belt's background population when applying the hierarchical clustering method to its proper orbital elements. It orbits the Sun in the inner asteroid belt at a distance of 1.8–2.9 AU once every 3 years and 7 months (1,310 days; semi-major axis of 2.34 AU). Its orbit has an eccentricity of 0.23 and an inclination of 9° with respect to the ecliptic. The body's observation arc begins with its first observation as at Heidelberg Observatory on 28 August 1911, more than two years prior to its official discovery observation at Vienna Observatory.

Naming
This minor planet was likely named after Nora Helmer, the heroine in the play A Doll's House (1879) by Norwegian poet Henrik Ibsen (1828–1906). The name was given by the discoverer's friends. The was also mentioned in The Names of the Minor Planets by Paul Herget in 1955 (H 78).

Physical characteristics
In the Bus–Binzel SMASS classification, Nora is a common, carbonaceous C-type asteroid. In the Tholen classification it is one of few asteroids considered unclassifiable.

Rotation period
In March 2018, a rotational lightcurve of Nora was obtained from photometric observations by Tom Polakis at the Command Module Observatory in Arizona. Lightcurve analysis gave a rotation period of $38.719 km$ hours with a low brightness variation of $39.58 km$ magnitude (U=2). The result supersedes previous observations by European astronomers at the La Silla, Haute Provence and Hoher List observatories during the 1990s which gave two periods of $40.02 km$ and $55.53 h$ with an amplitude of $0.064$ and $0.065$ magnitude, respectively (U=1/2−). In April 2007, French astronomer Arnaud Leroy determined a period of $0.068$ and a brightness variation of 0.01 magnitude (U=1).

Diameter and albedo
According to the surveys carried out by the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer (WISE), the Japanese Akari satellite, and the Infrared Astronomical Satellite IRAS, Nora measures ($55.53$), ($0.08$) and ($24 h$) kilometers in diameter and its surface has an albedo of ($34.4 h$), ($0.2$) and ($0.08$), respectively. The Collaborative Asteroid Lightcurve Link derives an albedo of 0.0404 and a diameter of 39.84 kilometers based on an absolute magnitude of 11.1. Alternative mean-diameter measurements published by the WISE team include ($9.6 h$), ($38.719$), ($39.58$), ($40.02$) and ($0.068$) with corresponding albedos of ($0.065$), ($0.064$), ($41.712 km$), ($42.407 km$) and ($43.41 km$). On 4 May 2004, an asteroid occultation of Nora gave a best-fit ellipse dimension of ($43.43 km$), with a poor quality rating of 1. These timed observations are taken when the asteroid passes in front of a distant star.