The earth’s orbit around the sun is not a perfect circle. Rather, it's just a smidge elliptical - that is, oval-shaped. As a result, the earth isn't the same distance from the sun at all times of the year.

The average distance from the earth to the sun is about 93 million miles. But that ranges from 91 million to about 94 and a half million over the course of a year. From time to time, I hear this change in earth-sun distance used to explain why we have seasons. After all, it makes sense that it would be warmer - summer - at the time of our closest approach to the sun. And colder - winter - when earth is farthest from the sun.

But there's a fundamental problem with that argument. When it's winter here, it's summer in the Southern Hemisphere, and vice versa. So the changes in distance between the sun and the earth can't be the cause of the seasons, because you can't have it both ways. Another way to look at this - solely from a Northern Hemisphere perspective - is to realize that the earth made its closest approach to the sun just about ten days ago - right smack dab in the middle of our winter.