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SYFY WIRE Bad Astronomy

Perihelion 2014!

By Phil Plait
Two images showing the Sun at aphelion in 2005 (left) versus perihelion six months earlier. Credit: Anthony Ayiomamitis

If youâre feeling particularly chummy with the Sun today, like you two seem really close for some reason, then you may be right: Today at 12:00 UTC (07:00 EST) the Earth is at perihelion, the point in its orbit when itâs closest to the Sun. At that time, the center of the Earth is 147,104,780 kilometers (91,406,672 miles) from the Sun.

The Earthâs orbit is an ellipse, so sometimes weâre farther from the Sun and sometimes closer (the farthest point is called aphelion). The average distance of the Earth from the Sun is about 149,597,871 km (just a hair under 93 million milesâthis distance is called an Astronomical Unit or AU), but due to the eccentricity (the ellipticalness, to coin a word) of the orbit that distance can vary by about two or so million kilometers either way.

I know, for most folks itâll seem weird that weâre closest to the Sun in the dead of winterâthe solstice was only a couple of weeks ago!âbut the seasons have very little to do with our distance from the Sun. There is a small effect, but itâs totally swamped by the fact that the Earth is tilted by about 24 degrees relative to its orbit.

Last year, when we were at perihelion (on Jan. 2, 2013) I wrote a lengthy explanation of it, including this fun picture:

One of those is a perfect circle, and the other an ellipse scaled to match the shape of Earthâs orbit. Can you tell which is which?

The one on the right is the ellipse. Itâs pretty amazing, but if you shrank the Earthâs orbit down to this size, itâs barely distinguishable from a circle. But that ellipticity, small as it is, does have an effect on temperature, the length of our day, and even the timing of sunrises and sunsets!

So if you get a chance, go outside today and feel the sunlight on your skin ⦠and consider that it took 8.18 minutes to reach you from the Sun, about 16 seconds less than it will take to reach you when the Earth is next at aphelion ⦠on July 4, 2014.

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