Question: There are three problems with the setting of *Game of Thrones*: 

1. Because if the continent of Westeros in the show (and books) are probably set on either a parallel Earth or a very Earth-like alien world.
2. But the problem is that we find out that there are roughly forty years of winter for every ten years of summer (it could be more or less) so this planet is obviously not Earth because it must have a very different orbit to our world. It obviously takes fifty Earth years to orbit their sun and the planet is only positioned for summer for a short period of that time.
3. But we see in the opening credits that Westeros is inside the shell of a planet and at the centre is their large mechanical artificial sun, I don't think the opening credits of the show show us what is literally happening, I think it's an artists representation, so it's good to bear this point in mind but safe to ignore it.

So any ideas? 

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I believe I have confused some people with this question, first of all the story tells us something along the lines of "The summers last years and the winters last lifetimes!" I'm not sure what the exact wording is, but whether the tilt of the planet or the distance from the sun or the atmosphere is responsible is irrelevant, I think we can agree that it's not Earth or at least not our version of Earth. 

What I was hoping for was a little specific info on what this planet is for example, Lord of the Rings happens in a lost age in Europe, back when Elves, Hobbits and Dwarves shared the world with man, so we know Middle Earth, is Earth. Also we know Masters of the Universe happens on Eternia, Transformers happens on Earth and Cybertron so what planet does Game of Thrones happen on?

Answer: 
G.R.R. Martin is very keen on basing *invented* things in real ones, such as names (Geoffrey turns to Joffrey, for instance) or even food. Therefore, a planet which seems quite similar to Earth but its definitely not, is most likely the answer.

And for the Seasons length, as [Till B](https://scifi.stackexchange.com/questions/17093/what-planet-does-game-of-thrones-happen-on#comment31736_17093) says, Martin has stated that the [explanation](https://scifi.stackexchange.com/questions/3008/explanation-of-seasons-in-a-song-of-ice-and-fire) is magical, and will be given in the last book.
From the mouth of the creator himself;

"It's Earth. But it's not our Earth"
====================================

> 
> *[JH] This may be a silly question, but: When you think of the world you’ve created, where seasons last for years, where is it? It is another planet?*
> 
> 
> [GRRM] It’s what Tolkien wrote was “the secondary world.” **It’s not another planet. It’s Earth. But it’s not our Earth.** If you wanted to do a science fiction approach, you could call it an alternate world, but that sounds too science fictional. Tolkien really pioneered that with Middle Earth[sic]. He put in some vague things about tying it to our past, but that doesn’t really hold up. I have people constantly writing me with science fiction theories about the seasons — “It’s a double star system with a black dwarf and that would explain–” It’s fantasy, man, it’s magic.
> 
> 
> *- [A Dance With Dragons Interview, James Hibberd, July 12, 2011](http://ew.com/article/2011/07/12/george-martin-talks-a-dance-with-dragons/)*
> 
> 
> 

It seems that George may have changed his mind or updated his theory on the style choice to compare it to Middle-earth as an [earlier answer](https://scifi.stackexchange.com/a/56426/57310) in 1999 stated something similar, but in a more ambiguous way. I believe this interview in 2011 clears up some of this ambiguity and clearly draws the "secondary Earth" parallel.