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Implausibilibuddy t1_j27r5tq wrote

Reply to comment by Aseyhe in How fast does the Milky Way spin? How far does Earth move through space in a year? by Sabre-Tooth-Monkey

How does that work? I don't doubt it but it runs counter to my experience of kerbal space program orbital simulation software wherein an increase in orbital diameter requires an increase in velocity. Conversely, to decrease your altitude you must decrease your orbital velocity. 10 objects orbiting at the same velocity around a planet, in a perfectly circular orbit, will all be the exact same distance from the centre of the planet.

Actually, I've just looked up the moon's orbital velocity at 1km/s and low earth orbit as 7km/s so that's the complete opposite of what the simulation implies, which definitely requires prograde burns to increase apoapsis. I may need a layman's explanation for all this craziness.

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Aseyhe t1_j2838pk wrote

The difference is that you are thinking about orbits fully outside the gravitating body (the star, planet, or moon). In contrast, objects in a galaxy are orbiting inside an extended mass distribution. This means more distant objects feel the gravitational influence of more mass below them.

> Actually, I've just looked up the moon's orbital velocity at 1km/s and low earth orbit as 7km/s so that's the complete opposite of what the simulation implies, which definitely requires prograde burns to increase apoapsis.

Both are correct. You have to speed up to get to a higher orbit, and yet that results in you moving slower on average! As I noted in another comment, that is very interesting because it means gravitational systems have a negative heat capacity (adding energy cools them).

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Implausibilibuddy t1_j29fiwc wrote

That's a great point I hadn't considered, thanks!

The second point still breaks my brain, but I'm happy to take your word for it that both are true.

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