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In our own solar system, not all planets rotate in the same direction. Venus actually rotates west to east, very slowly. Its year is shorter than its day. Ura
by geuis 5y ago
In our own solar system, not all planets rotate in the same direction.
Venus actually rotates west to east, very slowly. Its year is shorter than its day.
Uranus rotates nearly 90 degrees in relation to the ecliptic.
Mercury rotates east to west, but has a special orbital resonance with Earth. Because its so close to the sun, for decades we could only see it well enough at certain points in its orbit. Because of the resonance, we basically always see the same face which made it appear to be tidally locked. It rotates quite fine, but it wasn't until the last couple of decades of sending probes by Mercury that its rotation could actually be detected.
There's just 3 examples in our own real solar system that disprove the "convention". Not even to mention the hundreds to thousands of other smaller bodies that are unique in their own ways.
- Groxx 5y agoI'm curious how Venus's direction is decided, since everything I can find claims it has no magnetic field (except one generated in the atmosphere). Given that: how do you define what rotational-pole is "north", to derive east/west? Or is it not based on a planet's qualities, in which case it's likely something solar, and then what would Uranus' "north" (or east) be?
- mcphage 5y agoLooking at it from above, wouldn’t one way be a clockwise rotation, and the other be a counterclockwise rotation?
- retsibsi 5y agoDepends on which 'above' you're looking from though, right? (edit: that wasn't meant to be obnoxiously rhetorical, just to signal that I might be messing up the visualisation myself.) If the planet is rotating around the axis from pole to pole, then from above one pole (or anywhere that side of the equator) the rotation will appear clockwise, from above the other pole it will appear anticlockwise, and from directly above the equator it will just be 'left' or 'right' (or forward or back) depending on your orientation. edit: perhaps from directly above the equator you would still consider the spin to be clockwise or anticlockwise -- but which one would depend on your orientation.
- mcphage 5y agoI would suggest using whatever we consider North for the sun—individually, what way is up doesn't matter, all that matters is we use the same direction for the whole solar sytem.
- SamBam 5y agoThe issue is what is "above." Using the elliptic plane is a fine answer, but is just a convention.
- mcphage 5y agoI guess, for above I'd use whatever we consider "North" for the sun.
- murderfs 5y agoIt's defined relative to the ecliptic plane: the north pole is the pole that's on the same side of the ecliptic plane as Earth's.
- deleted 5y ago[deleted]
- Groxx 5y agoSo it'd be ambiguous / splitting hairs for something arbitrarily near 90 degrees? And given that planets wobble, seems like that'd let poles flip arbitrarily quickly, which would be weird. Uranus might be too far off for this (~8 degrees is a lot more than Earth's wobble, it might take an impact to shift that far and then I think it's fair to reassess), but heck, it got to this point somehow, it'll happen somewhere else too. For relatively perpendicular though, yeah - that largely works I think. But then we should expect most to be "sun rises in the east" as, as far as I'm aware, most solar system bodies orbit and rotate in the same direction as their star does.
- anigbrowl 5y agoDid not know that about Mercury, still thought it was tidally locked. Thanks for pointing that out.
- alisonkisk 5y agoEast<->West is a homomorphism (there is no "up" in space), so you need at least 2 planets before you can meaningfully say that one of them doesn't rotate East to West.