2100 Ra-Shalom, provisional designation 1978 RA, is an eccentric, carbonaceous asteroid, classified as Aten asteroid and near-Earth object, about 2.7 kilometers in diameter. It was discovered by American astronomer Eleanor Helin at the U.S. Palomar Observatory in California, on 10 September 1978.
It was the second Aten asteroid to be discovered after 2062 Aten, the family's namesake, also discovered by Helin in 1976. The group of Aten asteroids feature a semi-major axis of less than 1 AU. Of this group, "Ra-Shalom" has one of the smallest semi-major axes, just 0.832 AU. It comes within 30 gigameter (Gm) of Mars, Earth, Venus, and Mercury. The closest approaches are to Mercury, to about 0.0784 AU (11.7 Gm). The asteroid orbits the Sun at a distance of 0.5–1.2 AU once every 0 years and 9 months (277 days). Its orbit has an eccentricity of 0.44 and an inclination of 16° with respect to the ecliptic.
It has a C-type and Xc-type spectrum on the Tholen and SMASS taxonomic scheme, respectively, and an Earth Minimum Orbit Intersection Distance (MOID) of nearly 0.15 AU, which is far too large to make it a potentially hazardous object.
Over the last two decades, a large number of photometric light-curve observations have determined a concurring, well-defined rotation period of 19.8 hours, while the body's albedo varies from 0.08 to 0.16 and its diameter lies in the range of 1.98 to 2.79 kilometers (also see infobox). Among these differing results, the Collaborative Asteroid Lightcurve Link (CALL) considers an albedo of 0.082 with a diameter of 2.78 kilometers as the most reliable result. In 1981, the asteroid was detected using radar, revealing a relatively smooth surface at decimeter scales.
The minor planet's composed named was chosen by the discoverer to commemorate the Camp David Peace Accords between Egypt and Israel in September 1978, and as a symbol for the universal hope for peace. Ra is the Egyptian Sun-god, who symbolizes enlightenment and life, while Shalom is the traditional Hebrew greeting meaning peace. Naming citation was published before November 1977 (M.P.C. 4548).