Why is summer hotter than winter?

I have found a interesting question at TED site.

Why is summer warmer than winter?

Is it because during summer, the earth gets closer to sun?
Then you might imagine ellipse shape of the path of earth around sun like this:
But actually it is not true. It is not ellipse.
In fact it never gets closer at all like this:

The real question is that why do we come up with the ellipse shape for the path?
I think it is because we have never experienced about solar system ever.
Or we have not had any chance to think about the path.
I have never seen the Mars by my eyes.
I have never checked any path of any star.

Lack of experience stupifys us.