Vesta, the brightest asteroid

by Tanya
Publish date
29 July 2011
Comments (1)

Now is your chance to see an asteroid from within the asteroid belt. Vesta will be at its best for the next few weeks and it is the only asteroid that can ever be seen with the naked eye. Even thought it's smaller and further away than the dwarf planet Ceres (the largest object in the asteroid belt), Vesta's surface is great at reflecting sunlight.

Mind you, it still won't be easy. Astronomers measure brightness in magnitudes and by historic convention, the lower the magnitude, the brighter the object. The Sun comes in at a whopping -27. Alpha Centauri, a famous bright star and the closest star to the Sun, clocks in at -0.3.

In comparison Vesta, at its brightest, will reach a magnitude of 5.6. That's only just above the naked eye limit. So you will have to get out to a dark location to see it. Of course with binoculars or a small telescope you'll be doing much better. Remember though, it's only 530km across, so it will only ever look star-like.

Finding chart for Vesta at 9pm on 5th August.Finding chart for Vesta looking eastward at 9pm on 5th August, prepared with the help of "Starry Night" software.
Source: Museum Victoria

So what's so special about now? Vesta will be at opposition on the 5th August, which means opposite the Sun in the sky. It will be in the sky all night and all of the Sun's light will be shining on it (just like a Full Moon occurs when the Moon is at opposition).

And there's more - objects are generally closer to us at opposition and this opposition will bring the asteroid particularly close - still 184 million km away, but 27 million km closer than last year.

NASA's Dawn Spacecraft was 5,200km from Vesta when it took this image.NASA's Dawn Spacecraft was 5,200km from Vesta when it took this image.

But for a really close view of Vesta, nothing can beat the Dawn Spacecraft which entered orbit around the asteroid just two weeks ago. Dawn is the first craft to orbit an asteroid and will stay with Vesta for a year before moving on to study Ceres.

Exploring Vesta is sure to uncover some fascinating science. Asteroids are the oldest objects in the Solar System and from them we hope to learn more about how the planets, including Earth, formed.

And did you know that we have more pieces of Vesta here on Earth, than we have of the Moon! It's clear that something crashed into Vesta creating a huge crater and all that rock was sent flying out into space. About 5 percent of all meteorites that fall to Earth are said to have come from that collision.

Asteroids are fascinating relics of the Solar System, if you've ever wanted to see one now's the time to do it.

Comments (1)

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Lucy 1 August, 2011 15:31
So interesting!!
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Updates on what's happening at Melbourne Museum, the Immigration Museum, Scienceworks, the Royal Exhibition Building, and beyond.