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Mon, 16 Jan 2017

Vesta at its brightest

Everyone’s heard of asteroids, but how many people have actually seen one? This is a good time to try, because the asteroid Vesta is currently at its brightest for the year and is high in the evening sky. Even small binoculars will show it, and it’s bright enough to be seen through light pollution.

What’s more, the famous Heavenly Twins, Castor and Pollux, in the constellation of Gemini, are providing a good signpost to its position this year. And if you don’t know where to find the Twins, the well-known constellation of Orion points at them. Orion and Gemini are rising in the east as soon as it gets dark, and by 8 pm are easily visible in the south-east or in the south later in the night.

Orion’s Belt of three stars in a line are unmistakable, and are easily spotted even from city skies. Below them and to their right is the bright star Rigel, while above them and to their left is the reddish star Betelgeuse. Draw a line From Rigel through Betelgeuse and you come to the constellation of Gemini, with its main stars being Castor and Pollux, as shown in the map below.

Gemini finder

Click the image to see a larger version

Having found Castor and Pollux, now use your binoculars to scan the area below Pollux, as shown on the next map. Vesta moves slowly night by night, so you’ll need to choose the position relevant to the night when you are viewing. The positions relate to 8 pm on the nights shown.

Vesta in 2017

Click to enlarge

How bright will it appear? Though it isn’t the largest, Vesta is the brightest of all the asteroids, and shines at sixth magnitude. Bright stars are first magnitude and the faintest visible to the eye in dark conditions are sixth magnitude.  But most of us will certainly need binoculars to see it. The faintest stars shown on the large-scale map are seventh magnitude. Vesta will look just the same as a star, even in a large telescope, because it is much smaller than a planet such as Mars or Jupiter. The only way you will be able to tell which is a star and which is Vesta is from its position, and the fact that it moves from night to night.

The easy way with a camera

If you have a good-quality camera and can control the exposures, try photographing the area with a telephoto setting and an exposure time of a second or so at ISO 1600 or higher. You should be able to record Vesta quite easily, even in a city sky. Try a few different exposure times, making sure you are focused on infinity. But with extreme telephoto settings and exposures more than a few seconds the stars will trail, and in a light-polluted sky the stars will be washed out by the light pollution.

Make sure the camera is very steadily mounted, ideally on a tripod. To avoid jogging the camera when you press the button to begin the exposure, use the ‘delayed exposure’ setting that you would use for getting yourself into the picture, on the 2 seconds or 3 seconds option rather than the usual 10 seconds.

For more hints on taking star photos, look at our handy help page.


Added by: Robin Scagell