Vesta during 2011

DAWN at Vesta

NASA's DAWN spacecraft entered orbit round Vesta on July 15/16 nearly 16000km from the asteroid. At this distance the 530km asteroid has an apparent diameter just under 2 degrees. This is nearly 4 times the apparent diameter of the full moon and about the size the Earth appears from the moon. DAWN's orbit will be lowered in the coming days. The spacecraft will stay in orbit round Vesta for a year before going onto Ceres, the largest asteroid, arriving there in February 2015. More details and a picture are on the NASA site.

Vesta from the Earth in 2011

Vesta is currently in Capricornus. It reaches opposition on August 5 when it will be magnitude 5.6, chart of Vesta's path in Capricornus.

Vesta will be a morning object moving through Sagittarius from mid January up to 2 April 2011 after which it moves into Capricornus until December when it enters Aquarius. It is stationary on June 24 after which it moves in a retrograde sense to the west until its second stationary position on 17 September when it resumes moving to the east.

Vesta is at opposition on August 5, when its magnitude will be 5.6. This will make it just visible to the unaided eye from a dark site on a moonless night - for those with sharp vision! It will of course be an easy binocular object

In the first half of the year, Vesta will principally be a morning object. By the beginning of July it will rise soon after 8pm NZST, so be reasonably easy to locate by 10 pm. During the first months of the year, Venus and Vesta will be moving on almost parallel paths. Venus will overtake the asteroid on February 9/10. In the morning sky on the 10th, Vesta and Venus will be just under half a degree apart, that is just less diameter of the full moon. A 4.86 magnitude star will be about a quarter degree from Vesta.

Vesta has a diameter of 530 km.   The orbital period is 3.63 years, its distance from the Sun varying between 2.15 and 2.57 AU, the orbit having an eccentricity if 0.09.   The orbit is inclined at 7.1° to the ecliptic. The opposition distance from the Earth varies between 1.14 AU and 1.57 AU.

Vesta's greatest distance from the Sun is only slightly more than Ceres' minimum distance.  Vesta is the brightest of the asteroids, at the best oppositions it does become a faint naked eye object.  It is the second largest asteroid, with a diameter just under 60% that of Ceres, but has a considerably lighter surface, reflecting some 42% of the light falling on it.  This, combined with Vesta's closer approach to the Sun, means Vesta is usually the brightest asteroid.

Vesta was the fourth Minor Planet or Asteroid to be discovered, being first observed as a minor planet in 1807 by H W Olbers at Bremen.   Because of its opposition brightness, it must, of course, have been seen naked eye many times before that, although as a faint star.