Monday, January 3, 2011

Feeling warmer?

Short post since I drove home from near Washington, D.C. today and I'm a bit tired (but happy to be in my own home again).  There was an important astronomical event today.

Believe it or not, the Earth is closer to the Sun today (January 3 around 2:00 pm EST) that it has been since last January.  The Earth, and all of the planets, orbit the Sun in ellipses, not circles, as discovered by Johannes Kepler around 1605 with his First Law of Planetary Motion.

 As you can see, the difference between perihelion (from the Greek peri or "near" + helios or "Sun") and aphelion (from the Greek apo or "away" + helios or "Sun") is only 3 million miles given the average distance of 93 million miles or about a 3% difference.

It's not enough to make a difference in temperature here on the surface (the reason we have seasons is the TILT of the Earth's axis, not our distance from the Sun) but a size difference can be seen in a telescopic image (view here).

One consequence of Kepler's Second Law of Planetary Motion is that the Earth moves faster in its orbit near perihelion than it does at aphelion (here's an animation).  It's not much of a difference, 18.8 miles per second versus 18.2 miles per second for maximum and minumum orbital velocities.

Sometimes people claim crazy shit about the Earth's orbit.  P.Z. Myers at Phyrangula recently posted an example.

Finally, pop your head out tonight and look up.  The Quadrantids meteor shower will be peaking after midnight (early Tuesday morning, January 4).  Look to the northeast.

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