The Moon’s current phase can significantly influence what you can see in the night sky. Phases of the moon tell you how illuminated the moon is. A crescent moon, for instance, tells you that only a thin crescent-shaped slice of the moon is lit up by the sun. Light from this slice reflects onto the earth, so when we look at the moon we see a crescent.
The quality of your stargazing session heavily depends on the amount of light being reflected by the moon. Moonlight acts like light pollution – it disperses in the atmosphere and spreads out, blocking many fainter objects in the sky. This isn’t a problem if you’re looking at the moon. For observing anything else, however, it creates a film of light over the sky that can obstruct fainter stars, planets and deep sky objects.
As far as phases of the moon are concerned, you can divide your skywatching goals into ‘Moon’ and ‘everything else’.
The best nights for Moon watching
You might think that a full moon night is best for looking at the moon. Weirdly enough, this isn’t true. Full moon nights are when the Moon’s surface reflects maximum sunlight. This makes it incredibly bright, and washes out most of the surface details. With binoculars or a telescope, it will also be painfully bright to look at.
To observe the moon, try to pick a night when the moon is in or close to its first or last quarter. At these phases, the moon is lit up enough that you can easily discern surface details like craters and valleys. It’s also not too bright – you should be able to look at it comfortably for lengths of time.
The best nights for everything else
Moonlight acts like light pollution – the light spreads through the atmosphere and obscures fainter stars and DSOs. If you want to look at stars, planets and Deep Sky Objects (DSOs), the best way to ensure that you see as much as possible is to avoid the moon at all costs. A new moon night is perfect for this – the new moon sets by sunset, so the sky will be completely dark on these nights, allowing you to see significantly more. The waxing / waning crescent nights close to the new moon will also be ideal.
In a nutshell, moonlight can hinder your stargazing sessions, so check what phase the moon is in on an observing night. Pick a first/last quarter to moonwatch, and a new/crescent moon to look at anything else.
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