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Thursday, February 11, 2010


Opposition of Vesta February 2010

The North-east horizon as seen in Australia at 11 pm local daylight saving time (10:00 pm non-daylight saving time) showing the location of Vesta (click to embiggen) on the 10th of February.

While Mars is the focus at the moment, another opposition is upon us. That of the asteroid Vesta. Remember, an opposition is any time we are directly between an astronomical object and the Earth. Oppositions of Mars and Jupiter can be spectacular, but even humble chunks of rock can have oppositions. We generally don’t notice them, because they are invisible to the unaided eye.

One asteroid is an exception. At certain times the asteroid Vesta (hardly a humble chunk of rock, but the 4th largest asteroid) is visible to the unaided eye. Okay, so its magnitude 6, at the threshold of the eyes ability to see, and even in a strong amateur telescope, Vesta is a featureless dot. But still you are able to see a real asteroid, that was once counted as a planet, a left-over from the era of the formation of the Solar system.

This year, Vesta is not only visible (just, and then only if you are out at dark sky sites away from city lights), but it is relatively easy to find, being within a binocular field of the bright star Algieba (gamma Leonis) in the constellation of Leo. Algieba is the second brightest star in the distinctive, hook-shaped “sickle” of Leo which stars from the bright star Regulus. If you look to the north-east at around 11 pm local daylight saving time the sickle of Leo is clearly visible above the horizon to the right of distinctive red Mars (see Map above). Follow the sickle down from Regulus and you will find Algieba easily. Vesta will be off to the left of Algieba until the 16th, then it will be on the right. Vesta starts off on the 10th one and a half fingerwidths from Algieba, and gets closer every night until the 16th, when Vesta shoots between Algieba and the nearby 40 Leonis. There is only one other star as bright as Vesta within 2 fingerwidths radius of Algieba, and Vesta is obvious as it’s the one that moves from night to night.

Binocular Map showing the location of Vesta from 10-26 February, as seen through 10x50 binoculars (circle indicates field of view, click to embiggen) a printable PDF map is here.

Vesta will be at its brightest (and visible to the unaided eye) from 16-22 February, although it will be closest on 22 February (although it will take light 12 minutes to reach you from Vesta). While the challenge is to see Vesta with the unaided eye (again, you will need to be somewhere dark away from city lights to see Vesta without instruments), following Vesta in binoculars is very easy and highly rewarding.

You can test out your sketching skills by sketching the position of Vesta from night to night. The highlight of this opposition will be Vesta passing between Algieba and 40 Leonis on February 16th (update: see my observations here). This is best observed with binoculars or the low power eyepiece of a telescope (otherwise you won’t get both stars and Vesta in the field). Vesta moves fast enough that you can see it drift between the two bright stars.

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