David Aguilar (617) 495-7462
Christine Pulliam (617) 495-7463

What's New: Two Asteroids Synch Up

This month, the objects known as 1 Ceres and 4 Vesta approach each other in the sky more closely than they have since they were discovered. Ceres, which is now considered (at least according to the International Astronomical Union) both a dwarf planet and an asteroid, was discovered in 1801. It turned out to be the largest member of a belt of asteroids orbiting the Sun between Mars and Jupiter. Vesta, which was discovered six years later, turned out to be the second most-massive member of the Belt, and - as it turned out - the brightest. (In fact, under ideal conditions, Vesta can be seen with the naked eye).

By coincidence, both objects have been cruising in the same part of the sky. Both reached opposition in mid-April, when they were at their brightest and closest to Earth. But, as it happens, they appear closest to each other in July. On the evening of July 4 and 5, they will be separated by only 10 arc-minutes - one-third of the diameter of the Full Moon. They will appear in the same field of view of the average telescope even at high power!

Of course, recognizing them for what they are is another matter; they still appear as dimensionless points of light even in the most powerful telescope. But if you plot their motion against the background stars from night to night, you should be able to distinguish them.

Of course, this apparent alignment is only the view from our perspective on Earth; in space, Ceres lies 46 million miles beyond Vesta. One other thing they have in common: they have had - or will have - a visitor from Earth. The ion-powered spacecraft Dawn has already spent 14 months orbiting and mapping Vesta. It is now on its way to do the same job at Ceres, which it should reach in 2015. The difference between their appearance from distant Earth and a spacecraft close up is illustrated in the following images:

A global map of Vesta, made by the Dawn spacecraft in orbit around the asteroid (click image to enlarge*).

The best image of Ceres currently available, taken in 2007 by the Hubble Space Telescope. (click image to enlarge*).

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