There’s just no doubting that the single number 1 target of telescopes is Earth’s own satellite: The Moon. That’s right, THE Moon. Not “a” moon. THE Moon. 2nd in brightness only to the sun (albeit a very distant second) the Moon is usually the first thing a budding astronomer aims his first telescope at. And why not? Its big and easy to find. It is bright – so bright that it laughs at any effect light pollution would have on it. You can even view it when there are a few clouds in the sky.
The Moon, of course, goes through changes throughout the month. New Moon, Waxing Moon, Full Moon, Waning Moon. Of these, the Full Moon is perhaps the biggest siren call to folk who just got their first telescope. When people come out at night and see a full Moon they often think it would be a great target for a telescope. And when people with a telescope happen to step outside at night and see the full Moon their first instinct may well be to grab the telescope and bring it out for what is obviously an awesome astronomy target!
But its not.
Oh, its not bad. In fact aiming for a full Moon is actually a good way to learn how to use your telescope for the first time. Sometimes aiming the telescope in the dark can be a little bit trickier than it was in the living room. But the fact remains that while it is an easy target, it is not a very good target.
The problem is one of definition: The full Moon is full because the sunlight is falling straight onto it. This makes for a very bright Moon, but it also means that the details get washed out in the brightness. Even worse, since the sunlight is coming straight down on the Lunar surface there are no shadows being cast. This means that the mountains, craters and all the other surface features have almost no definition to them whatsoever. Sure you can see some details, but they get washed out. Even using a Moon Filter won’t help much as it doesn’t add any definition, just takes away the overexposed wash-out.
By comparison, a waxing or waning Moon is a much more detailed target. The sunlight is coming from the side of the Moon (at least from our perspective) and so all those crater edges, mountains, and seas now cast shadows that give them much greater definition.
If you look at the photo on the right you will notice that even though it is a much smaller photo than the full moon picture above, there is much more detail to be seen. Craters now stand out a lot more and you can see more of them. Other features now stand out a lot more as well, such as the contrast between the ‘seas’ and the other parts of the Lunar surface.
Now this surface is much more worthy of study, and it still bright enough that you can really crank up the magnification. Usually most astronomy hints will tell you to keep magnification moderate, but when it comes to the Moon, don’t be shy with it. Try and get the maximum recommended power out of your telescope (Which is 2x per mm of aperture or 50x per inch of aperture) and really enjoy close-up detail of the Lunar surface.
So remember, while the full Moon is very tempting, it is not really the best time to view the Lunar surface.
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