At 4 o’clock this afternoon, the earth will reach aphelion – that’s the point in our planet’s slightly elliptical orbit where it’s farthest from the sun. On average, we're about 93 million miles from the sun, but right now we are roughly 94 and a half million miles out. So how come we're having summer? Well, not everyone on earth is experiencing summer; winter has just begun for folks south of the equator. Our seasons aren't caused by any variation in the earth-sun distance; after all, that extra million and a half miles only makes for a tiny 2% difference. Temperature changes occur because our planet is tilted over a little, about 23 and a half degrees, from straight up and down. During summer in the northern hemisphere, the top half of earth leans inward, which puts the sun higher in our sky, and causes summer; in the winter the top half of earth leans away from the sun, putting it lower in our sky, which cools things down.