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Morning Mercury

May 23, 2010

The planet Mercury just peeks into view in the east a little before sunrise the next few days. But it's quite low in the sky, so it's hard to see. You need to be in the southern half of the country to have a realistic chance of spotting it.

The problem is geometry. Mercury lies along the ecliptic -- the Sun's path across the sky. At this time of year, the ecliptic is tilted at a low angle in the early morning, so objects along the ecliptic don't climb very high as they rise -- they just scoot along the horizon.

The tilt is more severe as you go farther north. By the time Mercury pops above the horizon, the Sun is just a little below the horizon, so it's already filling the sky with light.

The best chance to see Mercury comes from about Dallas or Los Angeles and points southward. The little planet is a few degrees above the eastern horizon around 30 to 45 minutes before sunrise. It looks like a fairly bright star. And there are no other bright planets or stars around it, so it has that region of sky all to itself. Even so, you need a clear horizon to see it.

For a really good view of Mercury, you'll need to head even farther south. From the southern hemisphere, the ecliptic arcs high overhead at sunrise, so Mercury is in good view. So if you just happen to find yourself in Sydney, Cape Town, or Buenos Aires, Mercury is a breeze to find. But from here in the States, it'll take a little work to see this elusive little planet.

Script by Damond Benningfield, Copyright 2010

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