1627 Ivar, provisional designation 1929 SH, is a stony asteroid and near-Earth object of the Amor group, approximately 9 kilometers in diameter. It was discovered on 25 September 1929, by Danish astronomer Ejnar Hertzsprung at Leiden Southern Station, annex to the Johannesburg Observatory in South Africa.
The S-type asteroid orbits the Sun at a distance of 1.1–2.6 AU once every 2 years and 6 months (929 days). Its orbit has an eccentricity of 0.40 and an inclination of 8° with respect to the ecliptic. Ivar's observation arc begins with its official discovery observation in 1929, as no precoveries were taken, and no prior identifications were made. It has an Earth minimum orbit intersection distance of 0.1124 AU (16,800,000 km). The eccentric Amor asteroid is also a Mars-crosser. In 2074, it will pass Earth at 0.141 AU, closer than it actually approached Mars in 1975 (0.150 AU).
A large number of rotational light-curves of Ivar have been obtained from photometric observations since 1985 (see infobox). They give a well-defined rotation period between 4.795 and 4.80 hours with a brightness variation between 0.27 and 1.16 magnitude, indicative of its non-spheroidal shape (also see 3D-model image). Future photometric observations will show whether the YORP effect will slowly change the body's spin rate (as seen with 1862 Apollo).
In 1985, the body was observed with radar from the Arecibo Observatory in Puerto Rico at a distance of 0.20 AU. The measured radar cross-section was 7.5 square kilometers.
According to the EXPLORENEOs survey carried out by the Spitzer Space Telescope, thermal infrared observations by the Keck Observatory, and NASA's Wide-field Infrared Survey Explorer with its subsequent NEOWISE mission, and thermal modeling by Alan Harris, Ivar measures between 8.37 and 10.2 kilometers in diameter, and it surface has an albedo between 0.09 and 0.15. The Collaborative Asteroid Lightcurve Link adopts an albedo of 0.151 and a diameter of 9.12 kilometers with an absolute magnitude of 12.87.
This minor planet was named by the discoverer in honor of his late brother Ivar Hertzsprung. Naming citation was published before November 1977 (M.P.C. 1860).