Eli5: Moon Phases

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Can someone please explain how/why we see the different phases of the moon (ie. Quarter, half, full, new, etc.). Where is the sun in relation to the moon and earth to produce the different moon phases? Thank you eli5! Bonus points for poorly drawn pictures.

In: Physics

2 Answers

Anonymous 0 Comments

Who needs poorly drawn pictures? Wikipedia has good-quality pictures!

https://upload.wikimedia.org/wikipedia/commons/4/46/Moon_phases_en.jpg

The sun always lights up half the moon. Whatever fraction of the moon that we can see lit up, that’s because of the angle between us and the lit-up side. So if you see only a small crescent of lit-up moon, it’s because the moon is mostly between us and the sun, and we can only see a small fraction of the lit-up side. But a full moon is when the moon is behind us relative to the sun, so we can see the entire lit-up side.

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