When Earth is closest to the Sun, it is winter in the northern hemisphere and summer in the southern hemisphere. Thus it is possible to see that Earth's distance from the Sun does not noticeably cause the seasons to change; the relatively minor effects of differences in distance is somewhat masked by the mainly oceanic southern hemisphere vs the half-continental northern hemisphere. Therefore, the Earth's seasons come and go mainly because Earth does not rotate with its axis exactly upright with respect to the plane of the Earth’s orbit around the sun. Earth's axial tilt is 23.5 degrees. This puts the Sun farther south in December and January, so the north has winter and the south has summer. Thus winter falls on that part of the globe where sunlight strikes least directly. Summer falls on that part of the globe where sunlight strikes most directly.