Monday, 2 March 2009

Did you know...

Full-moon is the worst phase to study through a telescope.

Astronomers, you see, thrive on shadow - like murderers. I'm in no way comparing our sky-gazing friends to our homicidal enemies know. At full-moon the moon is coated in the bright rays of the sun (lucky the moon is such a poor reflector of light or we might all be a little blinder by the morning). We need shadow for the contrast it creates.

Craters and mountains cast fantastic shadows when the sun's light is skimming the surface we can see and throwing darkness over the part we can't (or can just a little). The boundary between the 'day' and 'night' side of the moon is called the terminator. This terminator crosses the moon twice in a month, from new moon to full and back to new. Each night the dividing line moves a little, causing a different shadowy effect: either a little extra light beside a crater, or a longer shadow behind a mountain.

It's a real treat to watch the changing phases. But if you're going to walk in pitch darkness, aim for the full-moon; I hear it's pretty bright when there aren't clouds in the way.

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