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Astronomy: It's Like a Heat Wave

7-22-11 Sun and Planet NASA
The Sun … it’s coming. Credit: NASA

Writing a blog on a day when the temperature is expected to reach 96 degrees F with a heat index near 110, it’s hard to think about any celestial object other than the Sun. Although the Sun cannot really be blamed for this heat. The Sun is not any hotter today than it was a week ago. Day-to-day weather is caused by the atmosphere. And the Southern Hemisphere is trudging along with their regularly scheduled winter. In fact, Earth reached aphelion, its farthest point from the Sun, on July 4.

For the past several billion years since its birth, the Sun has been remarkably steady in its output, with occasional minor changes but nothing so severe as to keep life from flourishing on Earth. This is typical for a G-type main-sequence star like our Sun. G-type stars spend about 10 billion years busily converting hydrogen to helium. We are about midway through the Sun’s helium production phase. About 5 billion years from now, the Sun will run out of hydrogen for fuel, and that’s when Earth will really begin to feel the heat. The Sun will swell into a red giant, its outer layers bulging outward until it swallows Mercury, Venus, Earth, and probably Mars, too. As the sun’s heat nears Earth it will boil off the oceans and the atmosphere, leaving our planet a decidedly lifeless place well before it is enveloped in a solar embrace.

I bring this up not to alarm you, but to reassure you that our Sun still has a long happy life in front of it. Last night my friend was watching the movie The Road, based on Cormac McCarthy’s bleak book about an apocalyptic future. My friend made me promise her that the world will never end. The best I could promise her is that it wouldn’t happen in her lifetime. While a global nuclear war or deadly pandemic could surely decimate our Earthly population, neither of these things are guaranteed to happen and even if they did, I like to think that there will always be pockets of life that make it through the calamity. The fate of the Earth is assured by the eventual demise of the Sun, but that is such a long way down “the road,” that it is the least of our worries.

I made a point not to bring up meteor strikes. Nothing good can come from thinking about that.

The best you can do is go out and enjoy the hot summer day, or wait until the sun sets and the air begins to cool, then sit back and look at all the stars shining in the night sky. Look south at Scorpius the Scorpion with its low, looping tail and pincers facing west. See the brightest star by the head? That’s Antares, which is a red giant star. Imagine that it has finally reached this stage after billions and billions of years as a quiet, gentle Sun like ours. And then imagine that any inhabitants circling Antares have long ago discovered how to pack and move to a more suitable location before their own planet was eaten in the encroaching stellar atmosphere. Imagine whatever you want. There’s no rush. You have plenty of time.

-- Kelly Kizer Whitt loves clean, clear, and dark skies. Kelly studied English and Astronomy at the University of Wisconsin-Madison and worked for Astronomy magazine. She writes the SkyGuide for AstronomyToday.com. You can follow her on Twitter at twitter.com/Astronomommy.

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