Archive for November 8, 2016

11/08/2016 – Ephemeris – As the Moon wobbles

November 8, 2016 Comments off

Ephemeris for Election Day, Tuesday, November 8th.  The Sun will rise at 7:31.  It’ll be up for 9 hours and 50 minutes, setting at 5:21.  The Moon, 1 day past first quarter, will set at 1:14 tomorrow morning.

Tonight’s Moon bears close examination.  The Moon has an elliptical orbit of the Earth, so its motion around the Earth moves fastest when nearer and slower when farther from the Earth.  The Moon’s rotational speed, however is constant, Because of this the Moon appears to wobble back and forth.  It also nods a bit.  The effect is called libration.  As of yesterday the Moon was rotated its greatest to the right for the month.  It’s a small amount, only 8 degrees.  On the 18th only 10 days from now the moon will nod 8 degrees to the left.  A good way to tell the state of this libration for the waxing Moon is to check the position of the small gray sea near the right edge of the Moon, the Sea of Crises.  Now it’s right at the edge of the Moon.

Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.


Moon's libration animation

Simulation of the Moon’s phase and libration for October 2007 by Tomruen. Image is in the Public Domain.  Downloaded from the Wikipedia entry for the Moon.

You can run a continuous simulation like this using the free program Virtual Moon Atlas.




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