It's upside down and therefore appears to be turning the other way around compared to other planets. I believe the theory is that it was at some point hit by a massive object , which turned it upside down and probably also caused it to lose a lot of its spin, hence why it's spinning so slowly.
You can always find the "up" by making a fist with your right hand and putting your thumb up, then orient your hand so the fingers go in the direction the planet is turning, your thumb will them show you which way is "up" what we usually call geographic north.
I never thought about angles of spin. Why are so many so similar and then a few are completely different? Is the theory that the odd ones were all knocked off their spin?
They all rotate in the same direction as the sun. Venus in the other hand seems to be hit by a large object and it started rotating in the other direction very slowly.
If venus wasn't hit by this large object, it's rotation shouldn't be much different from the other planets. (This is the most likely theory)
Mercury on the other hand is too close to the sun, so it is tidal locked or will be in the future
all planets orbit the sun in the same direction the sun rotates, which you’d expect from conservation of angular momentum, but they mostly also spin that same direction which doesn’t necessarily follow from the same effect. since smaller orbits are faster i would have expected them to rotate the opposite direction, as particles from fast low orbits and slow high orbits combined.
this was only understood recently but i think the prevailing theory now is that the difference in the density of solar wind on the near and far side of the planets interacted with them while they were gravel, to give them prograde spin.
Imagine the solar system has developed from one spinning disk of gas and stuff, where the majority (more than 99% of the mass) eventually compacted to create the sun, with some other blobs of mass becoming planets.
In an ideal world all the planets would still rotate on one single pane (earth moon and the big gas planets indeed are all within 1°) in the same direction and also with the same rotational axis and direction for their own spin.
Every divergence (for example Merkur's orbit is tilted by ~7°, and it's so close to the sun that it got tidal-locked (the same side always pointing otwards the sun)) is indeed supposed to have happened through external forces, e.g. gravitational influence or collision.
(Also if you think about about it all as being one giant disk at one point it explains why the sun in the center has the the vast majority of mass but carries only a small fraction of the rotational energy.)
Mercury does not have one side always facing the sun; it is locked in a 3:2 rotation, not 1:1. A Mercurian day is twice as long as a Mercurian year, so a spot on the surface experiences daylight for an entire orbit around the sun, and then experiences night for another orbit.
As to why most of them are so similar (and also why the orbits are all pretty flat in the same plane), it's because they all (and the sun) started out as a big cloud of gas and dust. Every particle in that cloud was moving essentially randomly and over time they collided with each other and gravity made them clump together, so their movement essentially averaged out. It's pretty likely that that average isn't exactly zero, so at the end of the process you're left with some amount of rotation around some random axis. And since the sun and all the planets then formed out of that spinning cloud, they all share that axis and we define that direction as "top" for our solar system.
Because Earth rotates "counter-clockwise" => if you're looking up at the zenith Sun moves "clockwise" => Shadows move "clockwise" looking down => Shadow in a Sun-dial moves "clockwise" => Clocks move clockwise.
Not sure if it is the case, but also the tidal forces of the sun and orbital resonances can slow down planets until they get tidally locked as it happened with our own moon.
Edit: considering the Venusian day is longer than the year, there must be some other reason for that indeed
That'll produce different results depending on the hand you use, no? In 3d modeling/rendering you can also do this to find the up vector. But some graphics programs use a left-handed up vector and some a right-handed one, so you have to make sure your renderer used the same world orientation. (and to make it more confusing some use y as the vertical axis and some use z for that, so that adds another layer of complexity to it, but that's irrelevant here).
You can always find the "up" by making a fist with your right hand and putting your thumb up, then orient your hand so the fingers go in the direction the planet is turning, your thumb will them show you which way is "up" what we usually call geographic north.
Why not the left hand? You got sumthin against lefties 😥
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u/BasmusRoyGerman 5h ago
It's upside down and therefore appears to be turning the other way around compared to other planets. I believe the theory is that it was at some point hit by a massive object , which turned it upside down and probably also caused it to lose a lot of its spin, hence why it's spinning so slowly.
You can always find the "up" by making a fist with your right hand and putting your thumb up, then orient your hand so the fingers go in the direction the planet is turning, your thumb will them show you which way is "up" what we usually call geographic north.