More Moon and Planets

StarDate: June 11, 2013

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There’s a pretty good chance that the young Earth got a “big whack” — it was hit by a body as big as Mars. That spun up Earth’s rotation, and blasted out a huge amount of material, which quickly coalesced to form the Moon.

It’s possible that Venus got a big whack as well. The collision didn’t form a moon — at least not one that’s still around today. But it made Venus spin in the opposite direction from most of the other planets in the solar system.

As seen from above the solar system, Earth and most of the other planets rotate in a counterclockwise direction — the same direction in which they orbit the Sun. Venus also orbits in a counterclockwise direction, but it rotates clockwise.

What’s more, it takes the planet 243 days to complete one turn on its axis. The slow, backward rotation rate means that a “day” on Venus — the interval from one sunrise to the next — lasts 117 Earth days.

There’s no way for Venus to be born that way — the planets should all have been spinning in the same direction. So one possible scenario is that something hit the young planet and either flipped it upside down or caused it to reverse directions — putting a new spin on Earth’s closest planetary neighbor.

And Venus is in good view early this evening. It’s the brilliant “evening star” well to the lower right of the crescent Moon. The much-fainter planet Mercury is a little above Venus. Both worlds set not long after the sky gets good and dark.

 

Script by Damond Benningfield, Copyright 2013

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