July 5, 2012 - Earth at Aphelion

In the wintertime for me and billions of other Northern-Hemisphere types, the Earth was at its closest to the Sun (even though it was pretty much the coldest part of the year, for us). Now that the Northern Hemisphere is broiling under a summer Sun, we find out that Earth is at its farthest point from the Sun.

The farthest point of an elliptical (oval-shaped) orbit is called aphelion. And the Earth reached this point today at 3:33 UTC. (UTC means “Universal Time Coordinated.” It represents the time in Greenwich, England, which is seven hours later than my time in California, with Daylight Savings Time.)

Since the Earth's orbit is almost a circle, the difference between its aphelion (furthest point) and its perihelion (closest point) is very small (compared to the size of the orbit, that is!). There is only 3% difference between Earth's aphelion and perihelion. Earth's seasons and climate have nothing to do with this small difference in distance to the Sun. Instead, they are related to the tilt of the Earth on its axis and the resulting change in angle of the Sun's warming radiation.

Some solar system denizens have much more elliptical orbits. Pluto's orbit around the Sun is much less circular than Earth's, for example, and Halley's comet “circles” the sun in a really long, skinny oval.

Find out more about elliptical orbits at Windows to the Universe. Be sure to click the various links—for example, don't miss the interactive animation!

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