Number of Planets possibly up to 12.

The Sumerians did have a written language which limits the possible interpretations. One can only interpret a few things from the sentance "There are 7 planets". But since I havent found the exact text yet, it may be more vague than that.

As for the reclassifications, as I said before, Bring it on!!!

So, most moons would not qualify as the new class of dwarf planets, despite having the size. For example, Luna orbits Earth and is not fully tidally locked, so it wouldn't qualify, despite the size.

To be honest, I don't feel comfortable with this definition of the term "planet". If the Pluto-Charon system is defined as a double planet, then I would argue that the Earth-Moon system should be similarly defined. This is because the Moon has one very special orbital property that it does not share with any other large planetary satellite........

It actually orbits the Sun.

Originally posted by Mogget
To be honest, I don't feel comfortable with this definition of the term "planet". If the Pluto-Charon system is defined as a double planet, then I would argue that the Earth-Moon system should be similarly defined. This is because the Moon has one very special orbital property that it does not share with any other large planetary satellite........

It actually orbits the Sun.

Uh.... WHAT!?

You get three for that last, bolded comment of yours, my friend... Last time I checked, the Moon orbits around the Earth. Of course, the Earth, in turn, orbits the Sun, so I suppose in an round-about way you would be correct.

The main reason that the Pluto/Charon system differs the Earth/Luna system is that Pluto and Charon orbit around a point between the two boedies, while Luna clearly orbits around a point inside the Earth.

The reason the moon wouldn't qualify is that it's center of gravity lies within Earth. Pluto and Charon are a double planet because thier center of gravity lies in space between the two planets.

Uh.... WHAT!?

You get three for that last, bolded comment of yours, my friend... Last time I checked, the Moon orbits around the Earth. Of course, the Earth, in turn, orbits the Sun, so I suppose in an round-about way you would be correct.

OK, let me explain my comments.

Since the gravitational field strength of the Sun acting on the Moon is roughly twice that of the Earth, it could be argued that the Moon is actually in solar orbit, and the Earth simply "perturbs" that orbit. The situation is (of course) rather complex, but the theory is valid. The Moon is the only large satellite in the Solar System that is in this position, and that makes it unique. In my opinion, that is sufficient to class the Earth-Moon system as a double planet.

The reason the moon wouldn't qualify is that it's center of gravity lies within Earth. Pluto and Charon are a double planet because thier center of gravity lies in space between the two planets.

Yes, and I am saying that because the Sun exerts a significantly greater gravitational force on the Moon than the Earth does, the Moon should be considered as being in solar orbit. All other things considered, that would make the Moon a planet.


[edit on 18-8-2006 by Mogget]

[edit on 18-8-2006 by Mogget]

[edit on 18-8-2006 by Mogget]

Ah, very well stated. I hadn't even thought of it like that.

I still don't agree with you, though, solely for the fact that in Earth's perturbations of Luna's orbit it is caused to orbit around Earth.

Yes, it's fair to say that the Moon is in orbit around the Earth and the Sun. The reason that the Moon stays in orbit around the Earth is because of the fact that the Sun also exerts a force on the Earth. The overall result of this is that the "force difference" (for want of a better term) between the "Sun-Earth" and "Sun-Moon" interactions is quite small when compared to the singular force that the Earth exerts on the Moon.

So much of this debate reminds me of the "pile" problem in philosophy.

Take a pile of sand. When does a pile become a pile? If I add one grain of sand to an empty table, is that a pile? Usually not. How about if I add another grain of sand, is that a pile? No. How about three grains of sand? When we get to a hundred grains of sand, is that a pile? Maybe. If we had one more grain of sand, making 101 total grains, does it make sense for us to say, "a ha! now we really have a pile of sand."

The attempt to define what a planet is seems, ultimately in my eyes, arbitrary.

Here is a chart of other potential planets:

I like the definition the special IAU committee came up with and wholeheartedly agree with it. My one concern is that the number of planets will grow so large school children will stop memorizing them. So, unlike an earlier poster, I think the potential for future generations to know less about the bodies in our solar system is greater than it would have been had they opted for only eight planets.

There are only eight planets.

Ceres, Pluto, Charon, et al are going to be "dwarf planets." They'll be no more planets in the school children sense than the asteroids and comets are "minor planets." If anything, school books will still include these, if not only to touch on the subject of the "dwarf planets."

Ceres, Pluto, Charon, et al are going to be "dwarf planets."

If that's true, then the entire situation is pathetic. We might as well demote Pluto to the status of "KBO", and make do with eight major planets. It would make a lot more sense.

That's what they're doing...

Eight "Classical Planets"
A myriad of "Minor Planets" (This class has been around since the 1800s)
Currently around a dozen "Dwarf Planets"

Certainly once the barycenter of Earth/Luna is outside of Earth they'll have to reclassify the Moon, but until that time billions of years from now it'll stay a moon.

EDIT TO ADD:

Pluto would still be a KBO, but also a dwarf planet. Just like Ceres is still an asteroid, but also a dwarf planet. KBO is just the blanket term to classify everything that orbits between the orbit of Nepture and the Oort Cloud.

[edit on 8/20/2006 by cmdrkeenkid]

In other words, they prefer to complicate matters for no fathomable reason. What a pack of idiots.

I did some research and I found that the Moon is more gravitationally pulled by the Earth than by the sun, under the same manner in which the Earth's oceans are more pulled by the Moon than by the Sun.

So Mogget is wrong, if Pluto and Charon should be considered in a biplanetary system then Moon does not need to be considered in a biplanetary system with the Earth.

By the way Mogget you wouldn't happen to be one of those Neo-Pagan or Druids that worship the Moon now would you?

[edit on 24-8-2006 by Timeseer]

Your "research" is flawed. The Sun's gravitational force acting on the Moon is greater than that of the Earth. The Sun's tidal force acting on the Moon is weaker than that of the Earth.

This is because the force of gravity obeys an inverse square law. That means that if you double the distance, the force of gravity drops by a factor of 4.

Tidal force obeys an inverse cube law. This means that if you double the distance, the tidal force drops by a factor of 8.

In other words, tidal force drops off very quickly with distance. Why do you think that the Moon affects Earth's tides more than the Sun ? It's because even the Moon exerts a more powerful tidal force on the Earth than the Sun does.

For anyone interested, here's an updated map of the solar system
szyzyg.arm.ac.uk...

Here is te site for more info

szyzyg.arm.ac.uk...