Iris at Opposition in 2010/11

Iris will be in Gemini when it brightens to magnitude 9.5 early in October 2010 but moves on into Cancer on October 14. Its easterly movement takes it near Praesepe, the Beehive, star cluster, Iris is about 3.5° south of the cluster in early November.

Iris is stationary on December 10, but doesn't reach opposition until 2011 January 24, when it will be at magnitude 7.9, making it reasonably favourable. Following opposition Iris fades much rather more quickly than it brightened before it, dropping to 9.5 by late March. In late February the retrograde motion of the asteroid takes it briefly back into Gemini. It is stationary for a second time on March 6 and subsequently returns to Cancer on March 23.

The distance of Iris from the Sun varies between 1.833 and 2.937 AU, so that at the most favourable oppositions the asteroid is about 0.83 AU from the Earth. At the 2010 opposition the Iris is 2.16 AU from the Sun and 1.18 AU from the Earth. So the 2010 opposition is better than average.

At the poorest oppositions, eg in May 2012, Iris' brightest magnitude is 9.5. At the best oppositions it can be as bright as 6.7. No such opposition will occur in the near future.

Iris's diameter is 200 km. Its orbital period is 3.68 years, the orbit being inclined at 5.527° to the ecliptic. Iris was discovered in 1847 on August 13 by J R Hinds in London. This was his first asteroid discovery.