Earth at Perihelion
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An astronomy teacher's favorite trick question is this: What's the closest star? Well-prepared students raise their hands in unison to answer "Alpha Centauri," or if they're really sharp, Proxima Centauri -- the closest member of Alpha Centauri's three stars. The teacher smiles -- evilly, the unkind might say -- and springs the trap: No, the closest star is the one that shines all day long -- the Sun.
What brings this to mind is that the Sun is even closer than normal this week. Tomorrow, in fact, Earth will be closest to the Sun for the entire year -- a point in our orbit known as perihelion.
The average distance from Earth to the Sun is about 93 million miles. But the distance varies because Earth's orbit around the Sun isn't a circle. Instead, it's an ellipse -- like a circle that's been stretched out just a little. So over the course of the year, Earth's distance from the Sun varies by about three million miles. We're closest to the Sun in early January, and farthest in early July.
Even though we receive more energy from the Sun at perihelion, it's not really reflected in Earth's climate. The oceans and atmosphere store and distribute heat, keeping the climate relatively stable throughout the year -- a fact that might make another good question for the tricky science teacher.
Script by Damond Benningfield, Copyright 2007
For more skywatching tips, astronomy news, and much more, read StarDate magazine.