Little Boy Blue and the Man in the Moon

Photo Cred to Kaptain Kobold flickr account

Have you ever gone on a late night stroll and got the eerie feeling that someone was watching you?  As you gaze up into the night sky, you realize the eyes that have been haunting you belong to the "man in the moon."  No matter what time of night or where you are in the world, the "man in the moon" is peering down at you.  Have you ever wondered why?

Oded Aharonson, a professor of planetary science at the California Institute of Technology, has set out to explain exactly why the earth only sees one side of the moon.  As the earth is orbiting around the sun and spinning around its axis, the moon is also orbiting around the earth and spinning around its axis.  It so happens that the moon rotates once around its axis every time it rotates around the earth.  Mere coindidence?  Aharonson and team think not!




When the moon formed just over four billion years ago, Earth's gravity stretched it into and elongated football shape.  At that time, the moon spun around its axis much faster, so that every side of the moon was exposed to the earth at some point.  However, the earth's tidal forces continued to tug on the moon, forming a slight bulge on one side of the moon.  This bulge slowed down the rotation of the moon, locking it into its current orientation.

Previously many thought that it was just chance that "the man in the moon" faces the earth; however, Aharonson disagrees.  By analyzing the physics of the moon, taking into account its dissipation rate (how fast it can slow down its rotational energy).  Computer simulations of this predict that the "man it the moon" side will face the earth 100% of the time.  As for now, the eyes of the man in the moon will always be peering down from the night sky.

More information on this topic can be found here.