It was discovered on 18 February 1977, by Japanese astronomers Hiroki Kosai and Kiichirō Furukawa at the Kiso Observatory in Japan.

It is located in the leading Greek camp at the Gas Giant's L4 Lagrangian point, 60° ahead on its orbit (see Trojans in astronomy).

[7] In February 2013, a rotational lightcurve of Sinon was obtained from photometric observations by Lawrence Wasserman at Lowell Observatory and by Robert Stephens at the Center for Solar System Studies.

Lightcurve analysis gave a well-defined rotation period of 8.135±0.002 hours with a brightness amplitude of 0.72 magnitude, indicative of a non-spherical shape (U=3).

[7][8][a] According to the survey carried out by the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer, Sinon measures 37.86 kilometers in diameter and its surface has an albedo of 0.093,[6] while the Collaborative Asteroid Lightcurve Link assumes a standard albedo for a carbonaceous asteroid of 0.057 and calculates a diameter of 48.48 kilometers based on an absolute magnitude of 10.3.