http://www.space.com/searchforlife/seti_devore_solstice_021212.html [Broken]It is true that the Earth's distance from the Sun actually does vary during a year--but it is not enough to drive the seasons. The Earth's orbit is an ellipse with the Sun sitting at one foci. The closest approach of the Earth to the Sun is called perihelion, and happens on January 4, 2003 about two weeks after the winter solstice. Aphelion occurs when Earth is farthest from the Sun, and will happen on July 4, 2003, a couple of weeks after the summer solstice. The difference in distance? About 3 million miles, or about 3% of Earth’s total distance from the Sun, not nearly enough to explain the temperature difference between a cold day in January vs. a hot day July.