Earth is about to reach its farthest point from the sun. So why is it so hot?

A rising sun and Earth's horizon are featured in this image photographed by an Expedition 13 crewmember on the International Space Station.

Earth is about to reach aphelion, the planet's furthest point from the sun. (Image credit: NASA)

Temperatures in the Northern Hemisphere might be high, but on July 6, our planet will be at its farthest point from the sun this year. It's an annual occasion called aphelion, a term that comes from the Greek words "apo" (away) and "helios" (sun), according to Almanac.

If it seems counterintuitive for our planet to be at its farthest from the sun while you endure the summer heat, consider how Earth orbits the sun and how our planet rotates.

Astronomers refer to the average Earth-sun distance as an astronomical unit (AU), which is approximately 93 million miles (150 million kilometers), as defined by the International Astronomical Union (IAU). However, Earth's slightly elliptical orbit around the sun means that each year, there is one day when Earth is closest to the sun (perihelion) and one day when it's farthest from the sun (aphelion). In 2023, perihelion occurred on Jan. 4, when Earth was 0.98 AU from the sun. On July 6, at aphelion, Earth will be 1.01 AU from the sun, according to astronomer Fred Espenak.

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Although the difference between perihelion and aphelion can be millions of miles, it has very little impact on the temperatures on Earth. What causes the seasons is the 23.5-degree tilt of Earth's axis, which means the sun shines on different latitudes at different angles throughout the year. It's the axial tilt that causes the seasons. In July, the Northern Hemisphere is tilted toward the sun, receiving the full glare of our star in summer. Meanwhile, the Southern Hemisphere is tilted away from the sun, and days are shorter and colder there.

Although aphelion comes just a few weeks after the June solstice and perihelion arrives close to the December solstice, the events are not connected. The exact timing is caused by variations in the eccentricity of Earth's orbit, according to timeanddate.com, with the dates of perihelion and aphelion drifting by a day every 58 years since the 13th century.

Jamie Carter is a Cardiff, U.K.-based freelance science journalist and a regular contributor to Live Science. He is the author of A Stargazing Program For Beginners and co-author of The Eclipse Effect, and leads international stargazing and eclipse-chasing tours. His work appears regularly in Space.com, Forbes, New Scientist, BBC Sky at Night, Sky & Telescope, and other major science and astronomy publications. He is also the editor of WhenIsTheNextEclipse.com.