Replies

This geometric definition is not valid.

I guess we'll just disagree. While you can make the case that being or not being a 'wanderer' is independent of distance from the sun (so that 'loose' planets far from any star are still planets, and not rocks or whatever), the issue is whether Luna is a planet or a moon. If you took the earth away, then Luna would be a planet at any distance from the sun, so is your definition that distance from the sun doesn't make a body a planet, but distance from another body does?

My definition of the difference between moon and planet would be based on whether the gravitational attraction of the nearby 'planet' (in this case Earth) on the smaller body is greater or less than the gravitational attraction of the sun on that smaller body. In the case of Luna, the sun exerts a greater force than the Earth does.

Obviously, this sort of distinction - whether a particular body is considered a moon or a planet - depends exactly on whether there is another nearby planet which exerts a greater force on the body than the sun itself.

By that definition, though the moons of Jupiter and Saturn would continue to orbit the sun if the planet were removed, they are nonetheless moons because the force on them from their planet is greater than the force on them from the sun.

And this can be recognized by whether their motion is ever retrograde with respect to the sun or whether their motion is ever convex toward the sun.

You're welcome to your own definition any way you want to make it, but I think the gravitational force definition makes more sense. You are, of course, free to disagree.

And this can be recognized by whether their motion is ever retrograde with respect to the sun or whether their motion is ever convex toward the sun.

You're welcome to your own definition any way you want to make it, but I think the gravitational force definition makes more sense. You are, of course, free to disagree.

More or less gravity and whether or not the moon moves slower around a planet than the planet moves arond the sun (thus never being retrograde with respect to the sun) is not a good definition of being a moon. A moon is an object that would continue circling its primary in the absence of the sun. Thus, Saturn, which cirles around Jupiter, would not be a moon of Jupiter because it would go off on its own if the sun were gone. But a rock circling Jupiter slowly tens of millions of miles away would still be a moon of Jupiter if it would continue doing so in the absence of the sun. It is a satellite if it is gravitationally bound (not merely influenced or in resonance with a solar orbit) AT ALL to a primary other than the sun. What's more, scientists would call it a satellite of Jupiter just as they call the moon a satellite of earth except in the context of your silly contention.

And this can be recognized by whether their motion is ever retrograde with respect to the sun or whether their motion is ever convex toward the sun.

You're welcome to your own definition any way you want to make it, but I think the gravitational force definition makes more sense. You are, of course, free to disagree.

More or less gravity and whether or not the moon moves slower around a planet than the planet moves around the sun (thus never being retrograde with respect to the sun) is not a good definition of being a moon. A moon is an object that would continue circling its primary in the absence of the sun. Thus, Saturn, which circles around Jupiter, would not be a moon of Jupiter because it would go off on its own if the sun were gone. But a rock circling Jupiter slowly tens of millions of miles away would still be a moon of Jupiter if it would continue doing so in the absence of the sun. It is a satellite if it is gravitationally bound (not merely influenced or in resonance with a solar orbit) AT ALL to a primary other than the sun. What's more, scientists would call it a satellite of Jupiter just as they call the moon a satellite of earth except in the context of your silly contention.