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Astronomy: Bagging Neptune

Easy-to-spot Venus is the key to finding Neptune. Credit: John Chumack

Neptune is the most difficult planet for observers to check off their list. It is faint, at only magnitude 8.0, making it nearly impossible to distinguish from thousands of background stars. But every once in a while the farthest planet from the Sun drifts past another planet as seen from Earth. Using the closer and brighter planet as a guide, we then have a chance to spot the elusive Neptune.

Friday, January 13, 2012, is one such occasion. Venus, the brightest object in the night sky (the moon won’t be up) is easy to find as it glows brilliantly in the west after sunset. Using a pair of binoculars or a telescope, aim them at Venus. Just a little more than one degree to Venus’s right is Neptune. On this night, Neptune isn’t the closest point of light to Venus. Just below Venus is a star that shines at magnitude 6.9, and below that is an even brighter star at magnitude 4.2, Iota Aquarii. These distractions can actually help you spot Neptune.

If what you see when looking through the eyepiece is bright Venus with a small dot above it and a slightly brighter star above that, then you know that your telescope gives you an inverted view so you actually need to be looking to Venus’s left to find Neptune. Iota Aquarii is almost one degree away from Venus, so measure approximately that distance to Venus’s side (right or left depending on whether or not your view is inverted) to find Neptune.

Depending on how good your eyes and equipment are, you may see that Neptune has a bluish color and appears to be more of a disk and not pointlike, as the distant stars appear.

If your skies are cloudy on Friday, you can try again on Saturday, although Venus will already have moved farther away from Neptune, making their separation two degrees. Neptune will be to the lower right of Venus. Try looking just to Venus’s right for a trio of stars, then look just below them for one lonely point of light; this is Neptune.

Venus continues to climb upward away from Neptune each night. By February, Venus will be approaching the second most difficult planet to bag, Uranus. The Venus-Uranus encounter will be a much closer one, with the two planets appearing just 18 arcminutes, or less than a third of a degree, apart.

-- Kelly Kizer Whitt loves clean, clear, and dark skies. Kelly studied English and Astronomy at the University of Wisconsin-Madison and worked for Astronomy magazine. She writes the SkyGuide for AstronomyToday.com. You can follow her on Twitter at twitter.com/Astronomommy.

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