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date 14.Sep.2014

■ How come the moon rolls its eyes?

Who in their right minds would think of putting a stellar observatory at Greenwich? The place is overcast 90% of the time. I lived in the UK for 15 years and I can't remember watching a single full moon. Greece on the other hand is perfect for star gazing, especially in the summer months, where you would be unlucky to have a cloud spoil a full moon. Being able to observe then ask questions about the sun, the moon and the stars is one major factor that made ancient Greece the jewel it was.

We still like watching the night sky down here and ask ourselves the odd question. Everybody knows about the phases of the moon, and its moving in the sky in an arch like the sun does it — an illusion caused by the rotation of the earth. But have you ever noticed that the full moon, whilst remaining a circle throughout the night, it appears slightly different towards the end of its stroll, when it nears the horizon where it sets?

Most people see the moon when it first rises, and with a little imagination it looks like a face — some big craters look like eyes making the whole thing resemble a head. But only insomniacs would bother looking at it for long enough to realize that the face actually rotates as it moves in the heavens. How can that be?

The other day, the moon was in its waning phase, so it was quite big yet visible early in the morning and I was showing it to Vanessa (age 4), when I finally decided I must find an answer to this "rolling eyes" moon effect. With the help of the junior astronomer, we put together a mathematical model of the moon and used it to simulate the lunar orbit. And sure enough if you hold the drawing above your head, it looks like a proper face, but as you move it in a circle down towards the horizon, it appears to rotate like the moon does it. QED
the rolling face of the moon

So there you have it, all is not lost of that glorious ancient Greek spirit <g>. It's not about what other people (claim) they know, its about what one can figure out and understand for oneself. Thanks Socrates!

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