为什么地球有时候会比其他行星要靠近太阳啊?拜托啦!还有能多提供一些细节吗~~最好能翻译成英语的啊~~~~

Why is the EARTH sometimes closer to the SUN than the other planets are ?

地球和其它行星的轨道都是椭圆的，把太阳作为其中一个焦点，所以一年中有远近、四季。不知把什么翻成英文？
Why sometes the earth would be closer to the sun than other planets?

The distance of the eight planets in the solar system with the sun from near to far,in turn,are:mercury,Venus,earth,Mars,Jupiter,Saturn,Uranus,Neptune.Not far from our earth from the sun is not close,this makes the earth won't be hot,like mercury is not as cold as Neptune.And this is for the survival of life on earth provides a good condition.
This is very difficult to express clearly concrete to abstract understanding.
If volume and density is not so,for example,would not exist in the close to the sun,and close to the density and mass of the sun must satisfy this condition.,of course,why is this condition such as the upstairs said composition and condition of various factors,it is difficult to a one-time finish.