Aphelion

Context: Earth reaches aphelion every July. This year it did so on the 5th of July.

About Aphelion

• Aphelion is the point in the orbit of a celestial body (like a planet or comet) that is farthest from the Sun. Earth reaches aphelion around early July each year.
• Earth’s aphelion happens because its orbit is elliptical, not circular. All planets in the solar system move in oval-shaped orbits around the Sun, and this is probably true for planets around other stars too.
• Gravity is the reason behind these elliptical orbits. The planets pull on each other, making their orbits less circular. Jupiter, being the largest planet, has the most influence.
• The shape of an orbit is measured by its eccentricity: the higher the eccentricity, the more oval-shaped the orbit is. Mars has an eccentricity of 0.094, meaning its orbit is more elliptical. Pluto’s orbit is even more oval-shaped with an eccentricity of 0.244. In comparison, Earth’s orbit is almost circular with an eccentricity of 0.017.

How far is the Earth from the Sun at aphelion?

• At aphelion, Earth’s distance from the Sun is about 152.1 million km.
• Six months later, in early January, Earth reaches perihelion, the point at which it is closest to the Sun. At perihelion, the distance between Earth and the Sun is roughly 147.1 million km.

Does aphelion affect temperatures on Earth?

• The distance from the Sun is a common misconception for the cause of seasons.
• At aphelion, Earth receives 7% less sunlight, leading to milder summers and winters in the Northern Hemisphere.
• Earth is farthest from the Sun during aphelion, it doesn’t cause the coldest weather. The distance change is actually too small to significantly impact global temperatures.
• The main reason for seasons is the tilt of Earth’s axis, not the slight variations in distance to the Sun. As Earth orbits the Sun, the tilt means different hemispheres receive more direct sunlight at different times. This creates the cycle of summer, fall, winter, and spring.

What would happen if there were no aphelion?

• If Earth’s orbit were a perfect circle, the lengths of seasons would be equal, right now, spring and summer are a few days longer than fall and winter in the Northern Hemisphere.
• If Earth’s orbit became more eccentric, seasons in the Southern Hemisphere would become extreme. This could lead to intolerable summers and winters, causing crop failures and freezes.