Friday, March 20, 2009

The Evening AND Morning Star

This morning our conference is over, and I'm trying to tie up some loose ends before heading back to Austin (and then on to McDonald Observatory). I'll write a summary blog post on all of that in the next couple of days.

But I did want to point out that the next few days offers a rare opportunity -- to see the planet Venus in both the evening sky AND the morning sky on the same night.

This is possible because of geometry. Venus is closer to the sun than the Earth, so it goes around the sun faster. Every one and a half years, Venus "laps" the Earth, passing between the Earth and the sun. But the orbits of Earth and Venus are slightly tilted with respect to one another, so Venus usually passes just above or just below the Sun.

This lap, geometry works so that Venus is passing about 8 degrees (a little less than the width of your hand held at arm's length) north of the sun. That distance is far enough that people in the northern hemisphere who look for Venus low in the west right after sunset and low in the east right before sunrise will be able to see the planet, with the Earth blocking the sun.

If you are in the Northern Hemisphere and awake at both sunrise and sunset, try looking for Venus low in the sky at both times. You'll get a rare treat!

For some more information, try reading Sky and Telescope's blog post on Venus observing this month.

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