The Moon goes around the Earth every 29½ days, so the changing angle of sunlight on it causes its appearance to change night by night – its phases. Each evening you’ll see a bit more illuminated, and the Moon’s position in the sky changes. Now read on…

Thursday, 10 January

If it’s clear you’ll see a lovely crescent Moon over in the south-west, in the twilight sky. You’ll need to look in the early evening, because it gets quite low in the sky after about 8 pm.

Moon on 10 Jan
The Moon on 10 January 2019

Even with the naked eye you can see an obvious oval shape on the crescent. This is known as Mare Crisium – Latin for ‘Sea of Crises’. Of course, there’s no water on the Moon, but the Moon’s main features were named in the 17th century when people had no idea what the Moon was really like. The idea of seas seemed perfectly reasonable, and they gave all the dark areas similar romantic names, as we shall see over the next few days. By the way, the word Mare is usually pronounced ‘Mah-ray’ (except in Weston-super-Mare).

Another such dark area is right below Mare Crisium, known as Mare Fecunditatis, the Sea of Fertility.

This is a good time to see how much detail you can see on the Moon with the naked eye. Try doing a drawing and getting every detail accurate.

If you have binoculars take a look and you’ll see much more detail. There are lots of craters, which are particularly easy to see close to the shadow line.

You’ll probably notice that you can see the rest of the globe of the Moon shining faintly. But if the Moon is lit by the Sun, what’s lighting the rest of the globe? The answer is that it’s Earth. If you were standing on the Moon you’d see an almost full Earth in the sky, shining much more brightly than the full Moon ever does in our sky. Earth has lots of white clouds on its surface, and is about four time as large as the Moon, so the landscape is lit quite brightly even where the Sun is below the horizon. The light is known as Earthshine.

Earthshine on the crescent Moon. Photo: Robin Scagell

Question: Is Earthshine what moonmen call their illegally distilled whisky?
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