Earth's orbit about the sun is not perfectly circular.  Like all planets, it is an ellipse with at least a little eccentricity, for Earth this being 0.0167.  This means that our planet's distance from the sun ranges from 94,509,460 miles to 91,402,640 miles.  This difference results in an almost seven percent difference in solar energy reaching us between periapsis and apoapsis.

Oddly, the northern hemisphere summer occurs when the sun is furthest away, and its winter when the sun is closest.  The effects of our 23.5 degree axial tilt clearly overwhelms the orbital eccentricity effect, although it factors into the Milankovitch cycles, developed by  Milutin Milanković.

Many pseudoscientists and other quacks have abused these facts to put forth their own "theories" about the seasons; for example, in his book Your Right to Know by the then living Master of ECKANKAR, "Sri" Darwin Gross, we are told that Earth's magnetic forces are pulled by the sun's greater distance, causing internal terrestrial heat to well up and "cause" summer.  Gross was apparently unaware of the elementary fact that when it is summer in the northern hemisphere it is winter in southern, and so forth.

I confess that the reason I know this so well is because at that time I was a member of ECKANKAR.  This issue probably did more to drive me back to my scientific childhood than anything else (though there were many other factors) and into a career and lifelong devotion to science and reason.  I suppose, ironically, I owe an intellectual debt to Darwin Gross (who died not long ago) and ECKANKAR for demonstrating how distressing the irrational life is and, consequently, how rewarding the rational life can be. ECKANKAR, by the way, is still with us, still strong and, yes, profitable and tax-exempt, with tens of thousands of followers.  They keep a pretty low profile, but are rather like Scientology in their tactics, from what I've recently read.