Earth is farthest from the Sun annually in early July, an astronomical event known as Aphelion. This timing often seems contradictory in the Northern Hemisphere because it occurs during the warmest part of the year. The varying distance to the Sun is a natural consequence of Earth’s orbital shape, but it is not the main influence on terrestrial temperatures.
Naming the Farthest and Closest Points
The maximum distance point in Earth’s orbit is formally called Aphelion, derived from Greek roots meaning “away from the Sun.” Conversely, the point at which Earth is closest to the Sun is called Perihelion, occurring approximately two weeks after the December solstice in early January. Aphelion typically falls between July 3rd and July 6th, though the exact date shifts slightly each year.
At Aphelion, Earth is approximately 94.5 million miles (152.1 million kilometers) from the Sun. At Perihelion, the distance shrinks to about 91.4 million miles (147.1 million kilometers). This results in a difference of about 3.1 million miles (5 million kilometers) over the course of the year.
Why Earth’s Orbit Changes Distance
The annual fluctuation in Earth’s distance from the Sun is a direct result of the geometry of its orbit. The planet’s path is not a perfect circle but is instead an ellipse, a slightly elongated or oval shape. This elliptical path is a consequence of gravitational forces and is described by Johannes Kepler’s first law of planetary motion.
The Sun is not located at the geometric center of this ellipse but rather at one of its two focal points. Because the Sun is offset from the center, the distance between the Earth and the Sun must naturally vary as the planet traverses its orbit.
The measure of how much an orbit deviates from a perfect circle is called orbital eccentricity. Earth’s orbit has a very low eccentricity, meaning it is only slightly oval. This minor deviation is enough to create the Aphelion and Perihelion points annually, resulting in a distance difference of only a little over three percent of the average Earth-Sun distance.
Distance Does Not Cause Seasons
The change in distance between Aphelion and Perihelion is too small to be the main factor controlling the seasons or surface temperature variations on Earth. If distance were the primary cause, both hemispheres would experience their warmest temperatures at Perihelion in January and their coldest at Aphelion in July, which is clearly not the case. The slight distance variation only causes a minor change in the solar energy received, about seven percent, which is overshadowed by the effect of the axial tilt.
The actual mechanism driving the seasons is Earth’s axial tilt, known as obliquity, which is fixed at approximately 23.5 degrees relative to its orbital plane. This tilt means that as Earth orbits the Sun, the Northern Hemisphere is tilted toward the Sun during its summer, while the Southern Hemisphere is tilted away.
When a hemisphere is tilted toward the Sun, solar rays strike the surface more directly, concentrating energy over a smaller area. This direct angle, combined with longer daylight hours, causes summer. Conversely, when tilted away, sunlight strikes at a shallower angle, spreading the energy and resulting in less heating and shorter days, causing winter.