Eros at Opposition in 2012

Eros is at opposition in early February when it will reach magnitude 8.55 from February 1 to 5 and be 8.6 or brighter between January 27 and February 11. It is actually closest to the Earth on January 31 with a distance of 0.179 Astronomical Units, just under 27 million kilometres. This is about 70 times the mean distance of the Moon. Hence Eros is a Near Earth Asteroid so being the first NEA to be discovered.

Full moon is on February 8 (NZDT) so there will be considerable moonlight at the time Eros is brightest. However Eros is always some distance from the moon so the asteroid is likely to be visible in binoculars.

Eros first brightens to magnitude 9.5 on December 29 as it moves from Leo Minor into Leo. It will then be well north of the celestial equator and low in New Zealand skies. Over the next few weeks during the period near opposition, Eros will be moving to the south as seen from the Earth, rather than the more normal west. After being in Leo, Eros will move into Sextans on January 20 and then cross Hydra during February. It will move into Antlia at the beginning of March as its magnitude drops back to 9.5.

The southerly motion will bring it higher into southern hemisphere skies. It is just south of the equator when brightest at the beginning of February. The north to south motion is similar to that of (1036) Ganymed, the largest NEA, which was at opposition at the end of October 2011 and brightened to magnitude 8.3.

Discovery and History of Eros.

Eros was discovered by G. Witt at Berlin on 1898 August 13. It was also observed a little earlier the same night by A. Chalois at Nice. It was the first asteroid to be discovered that crossed the orbit of Mars to make a close approach to the Earth. At its opposition in 1900/1901 and again at the close approach in 1931 the parallax of was used to determine the distance of the Sun. The parallax is the apparent change in position of Eros as seen from different parts of the Earth.

The previous best determinations of the Sun's distance had been made by observations of the transit of Venus in the 18th and 19th centuries. So it seems appropriate that Eros should make another close approach in 2012 with another transit of Venus also occurring in June. The determinations of the Sun's distance using Eros remained the most accurate until radar measures later in the 20th century.

Eros was visited by the NASA spacecraft NEAR Shoemaker in 2000 when the elongated shape of the asteroid was imaged. In 2001 it descended to the surface. Eros is roughly cylindrical with dimensions about 34km x 11km x 11 km.

Eros's orbital period is 1.761 years, just over 643 days. Its distance from the Sun varies from 1.134 to 1.78 AU with a mean distance 1.46 AU. Thus at aphelion it is beyond the orbit of Mars. The eccentricity of the orbit is 0.223 and its inclination to the ecliptic is 10.8°.

Favourable oppositions of Eros always occur close to the end of January. At that time the Earth is 0.985 AU from the Sun. At the closest oppositions Eros is 0.149 AU from the Earth. The last close opposition of Eros was 1975 January 23 with at a distance of 0.151 AU, the next is 2056 January 24 at 0.150 AU. The close oppositions occur alternately at intervals of 37 and 44 years.

---

Chart prepared using GUIDE 8.0. Program produced by Project Pluto.