Friday, March 9, 2012

Worlds: Mercury

If you think of Earth as home, then they're our next door neighbors. If you rather like to think of Earth as whizzing around the galaxy (at half a million miles per hour!), then they're our fellow travelers. Either way, this month is one of the best in years for viewing the other planets in our solar system. All five planets known to the ancients - Mercury, Venus, Mars, Jupiter, and Saturn - are visible in the sky this month, and you don't even need a telescope. All but Saturn and Mercury are easy to find just by going out at the right time and looking up in the right spot. And so I'm going to try to spot them all this month: You should give it a shot, too. Priority one is Mercury.

Taken by Mariner 10 in 1974. Until the 2008 visit from Messenger, only half of Mercury had ever been seen.

Mercury stays close to the Sun, so it's only visible when the Sun is far enough below the horizon that it's kind of dark, but not so far that Mercury is also below the horizon. This means you can theoretically see Mercury from about 30 minutes after sunset to about an hour and a half after sunset, but 30 minutes after sunset the sky is still too bright unless you know exactly where to look, and an hour and a half after sunset Mercury is so low on the horizon to be obscured by hills or trees. Realistically, you have about a 15 minute window about an hour after sunset. Get somewhere with as clear a view to the west as you can find, and look low, where the Sun was just before it set. Since all the planets are in the ecliptic plane, you can use Jupiter and Venus to help: They'll be the brightest looking 'stars' on that side of the sky, fairly close together. If you were to draw a line between them and extend it toward the horizon, they point to Mercury. Like this:


Mercury is going to be hard to find: I've never seen it myself. How the heck did ancient astronomers find this thing in the first place? A good pair of binoculars should make things easier. All you can do is try.

The window of opportunity ends in a few days, then Mercury will be below the horizon before it gets dark enough to see, so make this planet the first priority or you'll miss your chance.

Happily, all the other planets will be much easier to find, and the window of opportunity is longer, so I'll save those for another night. Get after Mercury ASAP.

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