OT: The solar system has 12 planets

[capnq]

henk brouwer said: what if Charon had been in an eleptical orbit, so the barycenter would sometimes be inside, and sometimes outside of pluto, would charon change planet-moon status during it's orbit?

If I'm understanding the definition of barycenter correctly, a barycenter does not move relative to the objects that define it.

[henk brouwer]

Hmm the barycentre is indeed defined by the *average* distance between the two objects. Still, if they are in eleptical orbits the distance to the barycentre can change, if I understand correctly, actually it would have to because the objects move closer to each other, so one or both of them have to get closer to the barycentre. the wiki page on 'center of mass'( http://en.wikipedia.org/wiki/Center_of_mass )has an animation of two objects orbiting around their barycentre in an eleptical orbit when you scroll down a bit. in this animation the distance between the objects and the barycentre changes. If the radius of one of them had been a bit over twice as large the barycentre would disapear in it for part of each orbit. (I really should do the math, but that scares me a bit actually, I just hope I'm right )

[Cipher7071]

It would seem that the barycenter for two perfectly spherical bodies would never move. But, if either or both were oddly shaped and rotating, then the barycenter could shift somewhat.

I find the definition of a pluton that depends on the object's origin compelling. Otherwise, how to decide according to size or orbit seems abitrary to me. They shouldn't spend too much time arguing over it, as much of the argument is semantic.

[ToddT]

Nah, i have a very cynical take on this. Given the perodic discussion as to whether pluto is a planet or not, and now the discovery of other objects almost as big, the ones pushing for planet status of the planets and ensuring pluto's status, or looking make a name for themselves to find other planets in the solar system, which is more glamorous, finding a large rock or a small planet. From what i remember, if pluto had been found several years later it would most likely not have been classified as a planet.
pluto was found while ppl where looking for a 9th planet that had been mathmatically calculated to exist, when it was found it was for smaller than expected, hence part of the reason to found the everelusive tenth planet. I think that was before they new the exist of the ort cloaud and kiper belt.

[Kamog]

Slick said:
Yes, and there is another planet in Earth's precise orbit exactly on the opposite side of the sun at all times so it can't be seen unless you leave the planet.

That's the counter-earth.

[Renegade 13]

The first estimates and predictions of Pluto's mass were far too high, I believe due to miscalculations of the mass of Neptune, which in turn affected the calculations of the mass of Pluto. When they thought it was the size of the Earth, it logically was designated a planet, and when the error was discovered it was a little late.

[ToddT]

i didn't remeber the details haven't really kept track of that stuff in any meaning full detail in years. This redefinition of what a planet it sis doesn't surprise me.

[Cipher7071]

You're right about one thing: Where egos are involved, what's logical will often take a back seat.

[Glyn]

It doesn’t matter how many objects are classified as planets. What real matters are the questions we study.

Teacher:
“Today class we are studding the inter planets and planetary systems. A planetary system is a planet with one or more moons. How many inter planets and planetary systems are there? Nine, right.”

[DeadZone]

Why cant it simply be

A planet is a solar body orbiting a star on its own stationary orbit, having some sort of atmosphere (remember, all nine "current" planets are believed to have one)

With a moon being a solar body that orbits a planet

This is how I always understood it growing up, and it makes complete sense to me

I suppose a size classification would make sense