Planet Earth reaches its most distant point from the sun for 2014 on July 4 – American Independence Day 2014 – at 0 hours UTC). That’s 7 p.m. Central Daylight Time in the U.S. on July 3. And it’s sort of an independence day for Earth, too. Woot, woot! Farthest from the sun! So why is it so hot outside for us in the N. Hemisphere?
Earth’s independence is limited and temporary. That’s because our world’s orbit is very nearly circular. We’re not that much farther away from the sun on July 3-4 than we ever are. Today, we’re about three million miles (five million kilometers) farther from the sun than we will be six months from now. That’s in contrast to our average distance from the sun of about 93 million miles (150 million km).
Astronomers call this point in Earth’s orbit its aphelion. The word aphelion comes from the Greek words apo meaning away, off, apart and helios (for the Greek god of the sun). Apart from the sun. That’s us, today.
Looking for Earth’s exact distance from the sun at aphelion? It’s 94,506,462 miles (152,093,481 km). Last year, on July 5, 2013, the Earth at aphelion was a tiny bit farther away, at 94,508,959 miles (152,097,427 km).
Why is it so hot outside for us in the N. Hemisphere? We’re always farthest from the sun in early July during a N. Hemisphere summer – and closest in January during a N. Hemisphere winter – and that’s a good illustration of the fact that it’s not the Earth’s distance from the sun that creates the seasons on our world.
Instead, the seasons result from Earth’s tilt on its axis. Right now, it’s summer in the Northern Hemisphere because the northern part of Earth is tilted most toward the sun.
Meanwhile, it’s winter in the S. Hemisphere because the southern part of Earth is tilted most away from the sun.
Okay? Earth’s varying distance from the sun doesn’t create the seasons. But it does affect the length of the seasons. That’s because, at our farthest from the sun, like now, Earth is traveling most slowly in its orbit. That makes summer the longest season in the N. Hemisphere and winter the longest season on the southern half of the globe.
Conversely, winter is the shortest season in the N. Hemisphere and summer is the shortest in the S. Hemisphere – in each instance, by nearly 5 days.
Happy Earth independence day, y’all!
Bottom line: Planet Earth reaches its most distant point from the sun for 2014 on July 4 at 0 hours UTC). That’s 7 p.m. Central Daylight Time on July 3, here in the U.S. Astronomers call this yearly point in Earth’s orbit our aphelion.