As I think was discussed recently in another thread here, and was pointed out by Isaac Asimov in one of his science essays a long time ago, if you were to plot the paths of the Earth and Moon through space, you'd find they are both approximately 12-sided convex polygons around the Sun, out of phase by pi/12. The Moon's path does not look like something a kid would draw with a Spirograph, contrary to popular opinion.
When you look at moons of other planets, their paths do look like a Spirograph drawing.
If you are having trouble visualizing this, imagine two horses racing around a standard horse racing track. On the first straightaway imagine horse 1 is in the lead. At the first turn, horse 2 gets the inside track and pulls ahead. On the back straightaway, horse 2 leads, but on the second turn, horse 1 gets the inside track and takes the lead back in the turn.
It probably wouldn't even occur to you to think of horse 2 as having done an orbit around horse 1, yet if there were a remote control camera mounted on horse 1, and you were controlling it from the stands and you were trying to keep horse 2 in view at all times, you'd find that you have had to rotate the camera around a full circle. So, from horse 1's frame of reference, horse 2 indeed did orbit it once!
Now imagine the horses on a modified track that instead of two straightaways and two half-circle turns has four straightaways and four quarter-circle turns. Now horse 1 thinks horse 2 circled it twice.
That's essentially what the Earth and Moon are doing, but there are 24 turns in the race course, and the straightaways are not there--as soon as you leave one turn you are starting the next. So, from Earth's point of view it looks like the Moon goes around us 12 times a year. But alien astronomers watching would be like spectators at the horse race--they'd just see two planets orbiting the Sun in nearly the same order, taking turns using the inside track to pull ahead.
Another way to look at it is to consider force ratios. For moons such as those of Mars, or Jupiter, or Saturn, and so on, if you look at the force on the moon from the planet, and the force on it from the Sun, you find the ratio of those two is greater than 1. The planet "pulls harder" than the Sun does.
For the Earth and Moon, the ratio is less than 1. The Sun is pulling harder on the Moon than the Earth is!
also, isn't the force ratio issue more an issue of the inverse square law than anything else?
That still wouldn't make the Moon a planet though.
If the same happened to Jupiter, all of those moons would fly out of of the solar system. (Or at least go cometary.) None of the orbits would survive.
If this is the definition, then lets also report that Saturn now has a gazillion moons.
As an extreme example, if the cloud of asteroids was entirely concentrated in the earth's orbit that would increase the odds of a collision. So wouldn't discovering that there's always one increase the odds (by a lot less)?
The number of pieces on a chessboard matters very little. You could be winning or losing based on their arrangement.
Shit, this could be alarming. I'm gonna research this more. (Anybody here see Melancholia?)
2006 RH120 is a tiny near-Earth asteroid with a diameter of about five metres, which ordinarily orbits the Sun but makes close approaches to the Earth–Moon system every twenty years or so. Occasionally the object temporarily enters Earth orbit through temporary satellite capture (TSC).
The only exception I can think of at the moment are natural satellites which are part of a greater planetary ring...
Its pretty much the same as naming our planet the Earth, a pretty generic name for a planet.
