Planets and moons

[Whickerman]

Is Pluto a planet?

Does the earth have 4 moons?

[Loosehead]

Yes

No

[rojash]

Pluto is a dog

The earth has New moon, half moon, waxing moon, waning moon, 1st and 2nd quarter moons, blue moon, and big moon rising.

[Salamander]

Try this link

[Loosehead]

As Salamander points out, there is some doubt as to whether Pluto is a planet. This os for various reasons, offset orbital plane and also it ducks inside the orbit of Neptune occasionally. If it where discovered today it may well not be classed as a planet but as it wasn't it is treated as a planet.

[Whickerman]

Thanks on teh pluto thing

As for moons - there's the big one we know, and cruithne, but I'd heard there were two others?

[CT]

Yeah there's a few small asteroids that have odd orbits around earth, and probably a few other small rocks that we haven't noticed yet.

[bernardo]

Pluto is either yes a planet (if you define it to be one) or no, not a planet (if you define it to be not a planet). If it is defined as a planet, then it would be fair to count Sedna, Xena and Quaoar as planets as well. I prefer to think of it as not a planet, because it is substantially smaller than the other planets, and it has an unusual eccentric orbit. The danger of classifying it as a planet would be to open the floodgates for a large number of other Kuiper Belt Objects to be called planets in future if they are discovered. I think that the most sensible way of distinguishing between planets and non-planets would be to have an arbitrary limit on size e.g. 3000 mile diameter.

[ianess]

Interesting point you make bernardo but how and where do you draw the line?
Using the 3000 mile diameter would start a new argument as to whether Callisto,
Ganymede, and Titan in our own Solar System should be reclassified as planets rather than moons.
No doubt the debate on the subject will outlive us all.

[bernardo]

I am not sure, but I think that the 3000 mile limit was suggested by the Patrick Moore. The big moons of Jupiter & Saturn would still count as moons because they are moons around a big planet rather than floating about on their own.

[CT]

I think they should probably be classed as icy-planetoids (the KBO's) or something similar. Seemsthat we may find more of these things the further out we look. They would then be part of the third grouping of planet types, after the earth-like inner rocky planets and the gas giants.

[elginsmarble]

Yes. Pluto is a planet.

And yes. Pluto is also a dog.

Earth has one moon: called Moon.

[WaldoMcFroog]

Pluto is no longer a planet, as of today!

http://news.bbc.co.uk/1/hi/world/5282440.stm