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What you will learn in Moons and Natural Satellites

1. Why the Moon changes shape
Nothing paints a crescent. One light from the Sun falls on a ball, half of it is always lit, and the shape you see is that half from wherever Earth happens to be standing. Earth's shadow is not in the formula at all.
2. One face, always
The Moon turns exactly once per orbit, so the same hemisphere faces us for ever. That is not a coincidence, it is not luck, and the other side is not dark.
3. Tides
The Moon pulls the oceans toward it, which explains one high tide. There are two. The missing idea is that a tide is a difference, not a pull.
4. Jupiter's four
Io, Europa and Ganymede are locked into a resonance that is not the 1 : 2 : 4 it is usually described as — and the thing that is exact about them is what melts Io.
5. Ocean worlds
Most of the liquid water in the Solar System is not on Earth. It is under the ice of moons, and a density read off a chart is the first clue that it is there.
6. Rings and the Roche limit
Close enough to a planet, a moon cannot hold itself together — and the distance at which that happens depends on what the moon is made of, which is why Saturn's rings sit where they do.
7. How many moons?
Saturn's moon count has more than tripled since 2019, and it will be out of date again by the time you read it. The honest answer to 'how many' is a number with a date on it.

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1. Why the Moon changes shape
Nothing paints a crescent. One light from the Sun falls on a ball, half of it is always lit, and the shape you see is that half from wherever Earth happens to be standing. Earth's shadow is not in the formula at all.
2. One face, always
The Moon turns exactly once per orbit, so the same hemisphere faces us for ever. That is not a coincidence, it is not luck, and the other side is not dark.
3. Tides
The Moon pulls the oceans toward it, which explains one high tide. There are two. The missing idea is that a tide is a difference, not a pull.
4. Jupiter's four
Io, Europa and Ganymede are locked into a resonance that is not the 1 : 2 : 4 it is usually described as — and the thing that is exact about them is what melts Io.
5. Ocean worlds
Most of the liquid water in the Solar System is not on Earth. It is under the ice of moons, and a density read off a chart is the first clue that it is there.
6. Rings and the Roche limit
Close enough to a planet, a moon cannot hold itself together — and the distance at which that happens depends on what the moon is made of, which is why Saturn's rings sit where they do.
7. How many moons?
Saturn's moon count has more than tripled since 2019, and it will be out of date again by the time you read it. The honest answer to 'how many' is a number with a date on it.