I looked a post where it showed planets rotation speed at 10hrs/sec. It had an arrow pointing out of what I assume to be the North Pole. For example, Venus had it’s North Pole pointing in the general opposite of the Earth’s North Pole.
In: Physics
the right hand rule.
it provides an unambiguous way to define a rotation no matter the frame of reference.
Take your thumb, stick it out. Then curl your fingers like they are holding something. The circular direction your fingers are pointing matches to the direction of rotation, your thumb matches to the North Pole.
Venus rotates backwards so it’s North Pole is opposite.
It’s kind of arbitrary. You look at the axis of rotation and one end will be the north the other end will be the south pole. Since in our solar system and most likely all solar systems all the planets spin pretty much on the same plane we just use the Earth to decide whats north and whats south.
It’s semi-arbitrary; the North poles of the planets are all defined so that they face in the same general direction (i.e. generally towards Polaris as opposed to away from it).
However, this leads to wonky situations like Uranus.
It is true that it is kind of arbitrary which is the North and which is the South on a planet. However to keep things consistent we have defined the North and South poles of a planet based on the direction of rotation. This is why Venus have its North and South pole different to the other planets in the solar system as it rotates the other way. Another possible way to define the North and South pole would have been based on its orbit around the star. However this does not always corespond to the rotation of the planet. For example Uranus is rotating at its side so that once an orbit the North pole is facing directly to the Sun. But the direction of rotation can always be established with certainty.
For a long time, north meant the same general direction as the earth’s north pole. When it was discovered that Venus’s rotated in the other direction, its day was described as retrograde, but it still had the same north as earth. Uranus is what made everything confusing, it’s nearly sideways rotation made us ask that does north really mean.
Right now there are two main camps, one says that North is the counterclockwise pole, the other that north is the same relative direction the earth’s pole points and the counterclockwise pole is the “positive” pole. In either case, measures like angle of inclination are taken from the counterclockwise pole.
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