You might not need to break out the T-shirts, but Earth is getting its maximum dose of sunlight today. That’s because we’re at perihelion — our closest point to the Sun for the entire year.

Earth’s average distance from the Sun is about 93 million miles. But our planet’s orbit is lopsided. So today, we’re about one and a half million miles closer than average. That means we receive a little bit more sunlight than average. We don’t actually feel the difference, though, because the oceans and atmosphere spread the heat around.

The date of perihelion isn’t fixed. Instead, it drifts through the calendar. Around the year 1246, it occurred on the winter solstice, in December. It moves a day later every 58 years or so. About 4,000 years from now, it’ll take place on the spring equinox, in March.

Even now, the date can wobble a day in either direction from year to year. Part of that is the result of Leap Year. The perihelion moves a few hours later on the calendar each year, on average, until Leap Year, when it drops back. But the change is also influenced by the Moon’s position in its orbit around Earth. At some points, the Moon’s gravity is moving us a little closer to the Sun, while at others it’s moving us a little farther.

One impact of the close approach is a difference in the length of the seasons. Earth moves fastest when it’s closest to the Sun, so winter is the shortest season in the northern hemisphere.
 

Script by Damond Benningfield