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Earth at Aphelion

July 5, 2015

You’ve probably never noticed it, but the Sun appears to change size a little bit over the course of a year. The Sun itself doesn't change, though. Instead, it looks bigger and smaller because the distance to the Sun changes — by about three-and-a-half percent.

That happens because Earth’s orbit around the Sun isn’t a circle. Instead, it’s an ellipse, which looks like a slightly flattened circle. The Sun is a bit off the center of the ellipse.

This orbit will carry us farthest from the Sun for the entire year tomorrow afternoon, at a distance of more than 94 million miles — about three million miles farther than we were back in January.

The change in distance affects how much energy we receive from the Sun: we get about seven percent more in January than in July. But Earth’s oceans and atmosphere are quite efficient at storing and distributing heat, so they keep our planet’s overall temperature pretty much the same year ’round.

One other effect of the elliptical orbit is that Earth’s orbital speed changes over the year. Our planet moves fastest when we’re closest to the Sun, and slowest when we’re farthest, as we are now. That stretches out the summer season in the northern hemisphere — it lasts about five-and-a-half days longer than in the southern hemisphere.

So enjoy the extra days of the summer season — days that are made possible by our planet’s lopsided orbit.

-- Script by Damond Benningfield, Copyright 2015

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