A planet’s perihelion is the point in its orbit where it comes closest to the Sun. The word comes from two Greek roots: “peri,” meaning near, and “helios,” meaning Sun. Because planets travel in oval-shaped (elliptical) orbits rather than perfect circles, their distance from the Sun constantly changes, and perihelion marks the moment that distance is at its minimum.
Why Orbits Have a Closest Point
Planets don’t orbit the Sun in perfect circles. They follow ellipses, which are stretched-out circles with two focal points instead of one center. The Sun sits at one of those focal points, not in the middle. This is Kepler’s First Law of Planetary Motion, established in the early 1600s and still fundamental to how we understand the solar system.
Because the Sun is off-center within the ellipse, a planet is inevitably closer to the Sun on one side of its orbit and farther away on the other. The closest point is the perihelion. The farthest point is the aphelion (from the Greek “apo,” meaning away). Every object orbiting the Sun, whether it’s a planet, comet, or asteroid, has both a perihelion and an aphelion.
What Happens at Perihelion
A planet doesn’t just get closer to the Sun at perihelion. It also speeds up. Gravity pulls harder when the distance is shorter, so a planet moves fastest at perihelion and slowest at aphelion. This is especially dramatic for objects with highly elongated orbits, like comets. As they approach perihelion, comets whip through the inner solar system at tremendous speed before slowing down again as they swing back out toward the far edges of their orbits.
For planets with nearly circular orbits, like Venus, the speed difference between perihelion and aphelion is small. For planets or objects with more stretched-out orbits, the contrast is striking.
Earth’s Perihelion
Earth reaches its perihelion in early January each year. At that point, the planet sits about 91.4 million miles (147.1 million km) from the Sun. At aphelion in early July, it’s about 94.5 million miles away. That’s a difference of roughly 3 million miles.
This timing surprises many people, since January is winter in the Northern Hemisphere. If Earth is closest to the Sun in January, why is it cold? The answer is that seasons are driven by the tilt of Earth’s axis, not by distance from the Sun. In January, the Northern Hemisphere is tilted away from the Sun, receiving less direct sunlight, while the Southern Hemisphere is tilted toward it. The distance difference at perihelion versus aphelion changes the total solar energy reaching Earth by only about 6%: roughly 3% above average at perihelion and 3% below average at aphelion. That’s not enough to override the much larger effect of axial tilt.
For 2026, Earth’s perihelion falls on January 3 at 17:00 UTC (noon Eastern Time, 11 a.m. Central). The exact date shifts slightly from year to year but stays in the first week of January.
The Same Idea With Different Names
Perihelion applies specifically to orbits around the Sun. Astronomers use different terms for closest approach depending on what’s being orbited. An object orbiting Earth, like the Moon or a satellite, reaches its closest point at perigee (“gee” from the Greek for Earth). A body orbiting another star reaches periastron (“astron” for star). The general, catch-all term for closest approach in any orbit is periapsis.
Mercury’s Perihelion and General Relativity
A planet’s perihelion doesn’t stay in the same spot forever. The point of closest approach slowly rotates around the Sun over time, a phenomenon called precession. All planetary orbits precess, mostly because the gravitational pull of other planets tugs on each orbit and shifts it slightly.
Mercury’s perihelion precession became one of the most famous puzzles in physics. Astronomers measured Mercury’s orbit precessing at 5,600 arcseconds per century (an arcsecond is 1/3,600 of a degree). Newton’s equations, accounting for the gravity of all the other planets, the slight deformation of the Sun from its rotation, and the fact that measurements are made from a non-stationary Earth, predicted 5,557 arcseconds per century. That left 43 arcseconds unaccounted for, a tiny but persistent discrepancy that Newtonian physics could not explain.
In 1915, Albert Einstein applied his new General Theory of Relativity to the problem. His equations predicted that the curvature of spacetime near the Sun would cause Mercury’s orbit to precess by exactly 43 extra arcseconds per century, with no adjustments needed. In curved spacetime, a planet doesn’t trace a static, repeating ellipse the way Newton’s theory describes. Instead, the ellipse itself slowly rotates. Einstein’s ability to account for Mercury’s anomalous precession was one of the earliest and most convincing confirmations of general relativity, and it remains a landmark result in the history of physics.