# Do we really know why astronomical objects rotate and orbit? And, why they are doing that in a certain direction?

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I mean, we know that earth is rotating “eastward” and orbiting “prograde” in relation to the sun. But why those directions? Considering that there is a westward rotation and a retrograde orbiting.

In: Physics

Well, back when all the planets formed, there were most likely a lot more than today. Those were the ones who would orbit the other direction or in a different angle. They’re not here anymore today because they collided with other planets and were destroyed. All the other ones that started orbiting into the same direction with the same angle kind of survived and are still around today

I can explain why some things spin and orbit in certain directions, but as to why nearly *everything* has spin, I’m drawing a blank, despite one of my skills being Astronomy Nerd 100.

Things orbit other things because of gravity. Gravity gets less powerful the further away from the source you get; objects in orbit are far enough away from the object they’re orbiting, and moving fast enough to its side, that they won’t get pulled in and consumed entirety, but the object they’re orbiting still pulls on them enough to change their direction of motion.

Why do orbiting objects almost always orbit in the same direction as the thing they’re orbiting? Let’s take a generic solar system as an example.

Stars spin. They do that because the clouds of gas and dust they form from start to spin during that process, creating a large spinning ball of star-embryo and a disk of gas and dust surrounding it.

Planets can also form from this disk. If they do, they all end up orbiting in the same direction as the star’s spin because all of the stellar disk was moving in the same direction when they formed. I believe this is the reason planets tend to spin in the same direction as their parent star, and I know it’s also why all of a star’s planets orbit it at the same angle.

The only times this does not seem to be true (like with Venus’s reversed spin), scientists tend to think something must have happened to the planet in its past to change it. I could be wrong, but I’m pretty sure they think Venus got hit with a very large object at some point, which slowed and reversed the direction of its spin. They believe something similar happened to Uranus to knock it on its side.

Sorry if that wasn’t ‘like I’m five’ language; I tried my best. Also sorry I can’t seem to remember why the universe seems to like spinning objects so much.

Edits for grammar mistakes and formatting.

Roll two balls towards each other. When they collide their forces will cancel each other out. The two balls after the collision will move in the direction of whichever had the greatest force.

Now apply that to billions of rocks orbiting a star. At first they orbit in all kinds of directions. But after millions of years of rocks colliding into each other their forces cancel out and those with the greatest force dominate, resulting in everything travelling in the same direction.

Apply that same logic to rocks coming together due to gravity to form a planet.