Earth was at its farthest point from the sun yesterday – So why is it so hot?

Posted at 10:18 AM, Jul 05, 2012
and last updated 2012-07-05 10:42:36-04

If the sun looked a little smaller than usual on the Fourth of July, it’s not your imagination: Earth was farther from the sun than on any other day this year.

That’s because the orbits of all the planets in our solar system are not perfectly circular. The orbits are elliptical in shape the sun is offset from center. Earth’s elliptical orbit means there will be a point each year when the planet is closest to the sun, called perihelion, and a point when it is farthest away, known as aphelion.

This Fourth of July Earth was at aphelion, 94,511,923 miles from the sun. On the flip side, this year’s perihelion was on January 3rd, when Earth was 92,955,807 miles from the sun.

On average, Earth is about three million miles (about 3%) farther from the sun at aphelion than at perihelion. As a result, the apparent size of the sun in the sky will be about 3 percent smaller, but you may not notice the difference.

So if Earth was farthest from the sun on the 4th, why was it so hot?

It has more to do with the seasons than the distance… The Earth’s tilt determines the seasons. Earth’s north-south axis is tilted by about 23.4 degrees, so during its orbit, the poles point in different directions from the sun. When the northern hemisphere is tilted toward the sun it is summer, away and it’s winter.

During our summer months we receive a longer duration of sunshine, so the day is longer and the night is shorter. Also the sunlight hits the ground more vertically. These two things together contribute to the difference in heating for the seasons.

Credit: National Geographic