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Happy Perihelion Day

January 4, 2014 Leave a comment

Winter started in the northern hemisphere, and summer began on the southern half of the planet, more than two weeks ago, but today marks Earth’s closest approach to the Sun during 2014.

Our planet reached the perihelion of its orbit at 12:00 UST (5:00 am MST). At that time the center of Earth was 147,104,780 kilometers away from the center of the Sun.

Earth does not orbit the Sun in a circle; instead, the planet follows an elliptical orbit. That means we are at times closer to the Sun and at times farther from the Sun.

The point at which we are the farthest from the Sun during the year is called aphelion.

The two benchmarks of Earth’s orbit do not fall on the same day each year. In fact, perihelion aligned with the winter solstice in the northern hemisphere back in 1246 AD. The two events will not again occur on the same day for a very long time. In fact, in the year 6000 AD perihelion will occur on the same day as the northern hemisphere’s spring equinox. Perihelion occurred on the summer solstice about 11,000 years ago.

By the way, seasons on Earth have very little to do with the planet’s distance from its star. We experience winter, spring, summer, and autumn primarily because Earth is tilted on its axis.

Aphelion comes in early July, when Earth will be about three percent farther from the Sun than it is today.

Image

Graphic courtesy National Atmospheric & Oceanic Administration

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The Sun at Earth’s perihelion on Jan. 2, 2013; Solar Dynamics Observatory image courtesy NASA.

Happy Summer!

June 21, 2013 Leave a comment

Summer has begun here in North America. Hooray!

I know, you are saying to yourself “What’s up with this guy, I’ve been out of school for weeks!” But, my friend, I’m not talking about the first day you got to sleep in. No, I’m talking about the solstice.

Earth’s two solstices occur because the planet is tilted on its axis. In the northern hemisphere, the 23.4 degree tilt from the ecliptic means that the north pole is closer to the sun than it is at any other time of the year.

The result is that the sun’s path across the sky in the northern hemisphere is longer than it will be on any other day of the year.

Down south, of course, it’s a different story. Today is the winter solstice there because the south pole is tilted as far away from the sun as it will be all year.

So, yes, go ahead and feel good about sleeping in this morning. You’ve got a long, long day in which to get outside and shake off all that lethargy. The sun won’t set in mid-latitude areas of North America until after 9:00 pm, and if you are living in the Great White North the sun will not set until quite a bit later than that.

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