Question

Question #578f9

Answer 1

Because the Earth moves in an elliptical orbit around the Sun, it varies.

Explanation:

We are actually closest to the sun on about the 3rd of January (called ‘perihelion’) and furthest from it 6 months later (called ‘aphelion’.) The difference amounts to about 3% of our orbital diameter, so in January we are `1.471xx10^11` m away and in June around `1.521xx10^11` m, in other words about 150 million kilometres or 93 million miles.

Just for info. the fact that all planets (and moons etc.) move in ellipses was Kepler’s 1st law (his other two are equally amazing feats of observational astronomy completed without the use of a telescope!) If you are interested see here.