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Moon and Mars

January 29, 2010

The full Moon has a "full" companion tonight -- the planet Mars. They're low in the east at nightfall, with Mars a little to the left of the Moon. The planet looks like a brilliant star -- so bright that its orange color should be obvious even through the glare of moonlight.

Like the full Moon, Mars is lining up opposite the Sun in our sky. It rises at sunset, climbs high overhead during the night, and sets around sunrise. It's brightest for the year, too -- it outshines everything else in the night sky except the Moon, two other planets, and one star.

This alignment is known as opposition. It occurs when Earth passes Mars in our planet's smaller, faster orbit around the Sun. It's the closest approach for the two planets, which is why Mars looks so bright.

Unfortunately, this isn't a great opposition -- Mars is still 62 million miles away. A few years ago, it passed just 35 million miles away.

It's so much farther this time because Mars is close to its farthest point from the Sun. The planet's orbit is much more elongated than Earth's is, so its distance from the Sun varies by tens of millions of miles, compared to just three million miles for Earth. A few years ago, we passed Mars near its closest approach to the Sun, so it was also a lot closer to Earth.

Even so, Mars is still putting on a grand display. It'll start to fade next month, but will remain bright and prominent throughout winter and spring.

Script by Damond Benningfield, Copyright 2009

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