Summer arrives today -- a moment known as the summer solstice. It's the longest day of the year in the northern hemisphere.
Now before you shoot off those emails telling us how we've completely messed up the date, just relax. You're right that here on Earth, summer started five days ago. What we're talking about today is summer on Mars.
In some ways, the seasons on Mars are quite similar to those on Earth. The planet has a thin atmosphere, which warms up during summer and cools off during winter. And since Mars's tilt on its axis is almost identical to Earth's, the Sun passes about the same height across the sky for the same latitude.
In other ways, though, the seasons on Earth and Mars are quite different. The difference is caused by the shape of the orbits. Earth's orbit is pretty close to circular, so our distance from the Sun doesn't change by much.
But Mars's orbit is much more stretched out, so its distance from the Sun varies by about 20 percent. Mars is farthest from the Sun during northern summer, and closest during northern winter. So summers in the northern hemisphere are a good bit cooler than in the south, while winters are a good bit warmer -- on Mars, that is.
And Mars is in good view early this evening. It's low in the west at nightfall and looks like a fairly bright orange star. The true star Regulus is just a little to its upper left, with the brighter planet Saturn a little farther along the same line.
Script by Damond Benningfield, Copyright 2008
For more skywatching tips, astronomy news, and much more, read StarDate magazine.
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