Did you know that Earth reaches its farthest point from the Sun about two weeks after the June solstice? This year, it happens on July 5! We call this point in Earth’s orbit around the Sun “aphelion.” Interestingly, we’re closest to our fiery star in the winter and farthest away in the hot summer. Learn all about perihelion and aphelion!
What Are Perihelion and Aphelion?
The terms perihelion and aphelion describe different points in the Earth’s orbit of the Sun.
Remember that the Earth orbits the Sun in an elliptical path—which is oval, not circular. This means that the Earth is about 3 million miles nearer to the Sun in January at its nearest point than in July at its farthest point.
- Aphelion is the point of the Earth’s orbit that is farthest away from the Sun.
- Perihelion is the point of the Earth’s orbit that is nearest to the Sun.
The words come from Ancient Greek, in which helios means “Sun,” apo means “far,” and peri means “close.”
Perihelion and Aphelion in 2021
In 2021, Earth is at perihelion on January 2 at 8:50 a.m. Eastern Time and at aphelion on July 5 at 6:27 p.m. Eastern Time.
At perihelion, Earth was 91,399,454 miles away from the Sun; at aphelion, it will be 94,510,886 miles away from the Sun.
When Are Aphelion and Perihelion?
- Aphelion always happens in early July. About two weeks after the June solstice, Earth is farthest from the Sun.
- Perihelion always happens in early January. About two weeks after the December Solstice, Earth is closest to the Sun.
Isn’t it interesting that the Earth is farthest from the Sun during the hot summer months and closest during the winter months?
- Though this doesn’t seem to make sense, it’s the not the distance from the Sun that causes our seasons. Seasons happen because Earth’s axis is tilted at an angle. It’s because Earth orbits the Sun on a tilt that our planet gets more or less of the Sun’s direct rays at different times of the year.
Did you know that the Moon’s orbit around the Earth is also elliptical? The point in the Moon’s orbit that is closest to the Earth is called the “perigee” and the point farthest from the Earth is known as the “apogee.” Perigee and Apogee are often confused.
Aphelion and Perihelion on Mars
Though aphelion and perihelion are terms mostly used in reference to Earth since it’s our home planet, they are also relevant to other planets orbiting the Sun. Every planet has points in the orbits when they are farthest or closest away from their star.
For example, planet Mars has an even more elliptical orbit than Earth. In comparison, Earth’s orbit seems almost circular; this almost-circular orbit may be why Earth’s climate is relatively stable.
Mars also has four seasons but they are twice as long because it takes about two Earth years for Mars to go around the Sun. The southern hemisphere of Mars has a warmer, shorter spring and summer than in the north, as Mars is closest to the Sun towards the end of southern spring. The southern winter is longer because Mars is farthest away from the Sun then, moving more slowly in its elliptical orbit around the Sun.
For Mars, going from a colder winter to a warmer spring can be quite dramatic.
Image credit: JPL.NASA.gov