Weather

Happy Aphelion Day: Earth is farthest from the Sun today

Earth is at aphelion, the furthest point from the Sun in its not-quite-circular orbit, on July 4, 2022. On January 4 we'll be 3.1 million miles closer at perihelion.

Posted Updated
Beaufort sunrise
By
Tony Rice
, NASA Ambassador

As temperatures rise into the 90s, you might guess that Earth is closer to the Sun now than during the winter months, but the opposite is true.

Earth is at aphelion, the farthest point from the Sun in its not-quite-circular orbit, on July 4, 2022. On January 4, we'll be 3.1 million miles closer at perihelion.

Aphelion does have an effect on our weather, but it is not what you might think.

The amount of energy Earth receives from the Sun varies by only about 3.5% over the year. Temperatures are lower in winter months because the Sun's rays reach us at more of an angle, spreading that energy out over a larger area. When the Sun is more directly overhead, the energy is more concentrated, raising temperatures,

This is easier to see when you look at it from the Sun's point of view in these images from the GOES-16 weather satellite that the WRAL Severe Weather team uses everyday in putting together forecasts.

Sun view of Earth on the solstices (Credit: NOAA/NASA)

The increased distance slows Earth's trip around the Sun about 1000 m/s (2237 mph) this time of year compared to perihelion in January. This impacts the length of the seasons. Spring and summer are about 93 days long, autumn and winter last about 89 days.

Aphelion on other planets

Astronomers describe the shape of an orbit as eccentricity, a number between zero and one. Zero is a perfect circle, and as long as that number doesn't reach 1 (a parabola), the planet, moon or whatever else, stays in orbit.

Earth has an eccentricity of 0.017, Venus is the most circular at 0.007. Mars has an eccentricity of 0.094 which has a big impact on its seasons. Summer on Mars is 25 days longer than winter and spring is 52 days longer than autumn.

Mars has four seasons just like Earth, but they last about twice as long. That’s because it takes about two Earth years for Mars to go around the sun. July 4, 2016 just happens to be the start of spring in the southern hemisphere on Mars, where Mars rovers Curiosity and Opportunity are exploring.

Pluto is the winner with an eccentricity of 0.244. Its orbit is so elliptical than it was actually closer to the Sun than Neptune between 1979 and 1999.

So summers are hotter in Australia, right?

You would think that even the small increase in the Sun's energy that the Earth receives around perihelion, would make for summers that are a little warmer in the southern hemisphere. The opposite is true here as well.

The northern hemisphere is about 3.5º F warmer over the year because there is so much more ocean than land south of the equator (80%/20% water/land vs. here in the northern hemisphere). This is easier to see when you look at the Earth from the poles:

more than 2/3rds of Earth's land is in the northern hemisphere

Water requires significantly more energy to increase its temperature than land. Think about that the next time you step out of the cool surf at the beach onto the hot sand.

Related Topics

 Credits 

Copyright 2024 by Capitol Broadcasting Company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.