Lots of bright lights will punctuate tonight’s sky — part of the coast-to-coast celebrations of Independence Day. But the biggest, brightest skylight of them all — the Sun — is actually a little smaller and fainter than usual. That’s because we’re farthest from the Sun for the entire year — a point in Earth’s orbit around the Sun called aphelion.
The distance to the Sun changes because Earth’s orbit is an ellipse, which looks like a circle that’s been stretched and flattened. The Sun is a bit off the center of the ellipse.
Today, this elliptical orbit has carried us to a distance of more than 94 million miles from the Sun — about three million miles farther than we were back in January.
The change in distance affects how much light and heat we receive from the Sun — about six percent more in January than in July. But Earth’s oceans and atmosphere are quite efficient at storing and distributing heat, so they keep the 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. We move fastest when we’re closest to the Sun, and slowest when we’re farthest, as we are now. That means that summer in the northern hemisphere 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 2012
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