Perihelion is the point in an orbit where a planet, asteroid, or comet is closest to the Sun. For Earth, that closest approach happens every year in early January, when our planet sits about 91.4 million miles (147.1 million km) from the Sun. The opposite point, when Earth is farthest from the Sun, is called aphelion and occurs in early July.
If that timing surprises you, you’re not alone. January is the dead of winter in the Northern Hemisphere, yet that’s when Earth is physically nearest to the Sun. Understanding why this doesn’t contradict what you know about seasons is one of the most useful things perihelion can teach you about how orbits actually work.
How Elliptical Orbits Create Perihelion
No planet orbits the Sun in a perfect circle. Every orbit is at least slightly elliptical, meaning it’s shaped like a stretched-out circle with the Sun sitting off-center at one focus of the ellipse. This geometry guarantees that every orbiting body has one point where it’s closest to the Sun (perihelion) and one point where it’s farthest (aphelion).
Earth’s orbit is very close to circular, but not quite. The difference between our closest and farthest distances from the Sun is roughly 3.1 million miles. That sounds enormous in everyday terms, but it’s only about a 3.3% variation on a 93-million-mile average distance. Other bodies have far more dramatic swings. A comet plunging in from the outer solar system, for instance, can have a perihelion inside Earth’s orbit and an aphelion beyond Neptune’s.
Why Earth Moves Faster at Perihelion
A planet doesn’t cruise through its orbit at a constant speed. When it’s closer to the Sun, the Sun’s gravity pulls harder, and the planet speeds up. When it’s farther away, it slows down. This behavior is described by Kepler’s Second Law of Planetary Motion: the line connecting a planet to the Sun sweeps out equal areas of space in equal amounts of time. For that to work geometrically, the planet has to cover more ground per second when it’s near the Sun and less when it’s far away.
For Earth, the speed difference is modest but measurable. At perihelion, our planet travels at about 30.3 km/s (roughly 67,700 mph). At aphelion six months later, that drops to about 29.3 km/s (around 65,500 mph). That 1 km/s difference is a direct consequence of the slight ellipticity of our orbit. It also means Earth’s Northern Hemisphere winter is technically a bit shorter than its summer, because the planet is moving faster through that portion of its orbit.
Why Perihelion Doesn’t Control the Seasons
This is the question most people really want answered: if Earth is closest to the Sun in January, why is January so cold in the Northern Hemisphere? The answer is that distance from the Sun has almost nothing to do with the seasons. What drives them is Earth’s axial tilt of 23.4 degrees.
Because Earth’s axis is tilted relative to its orbital plane, the Northern and Southern Hemispheres take turns leaning toward the Sun as Earth completes its yearly orbit. When the Northern Hemisphere tilts toward the Sun (June), sunlight strikes at a more direct angle and days are longer, producing summer. When it tilts away (December), sunlight arrives at a shallow angle and days are short, producing winter. If Earth’s axis were perfectly upright with no tilt, there would be no seasons at all, regardless of the orbit’s shape.
The extra solar energy Earth receives at perihelion compared to aphelion is real, but small. Sunlight is about 6% more intense in early January than in early July. That 6% boost is spread across the entire globe simultaneously and is dwarfed by the effect of axial tilt on any given hemisphere. The tilt determines which hemisphere gets concentrated, long-duration sunlight, and that’s what creates the temperature swings we experience as seasons.
It’s also worth knowing that the timing of perihelion relative to the solstices is a coincidence of our current era. Earth’s closest approach currently lands about two weeks after the December solstice, but that alignment slowly shifts over time through a process called apsidal precession.
How Perihelion’s Date Shifts Over Millennia
The orientation of Earth’s elliptical orbit isn’t fixed in space. It gradually rotates, causing the date of perihelion to drift later in the calendar year over very long timescales. This full rotation, called the cycle of apsidal precession, takes about 112,000 years to complete. Thousands of years from now, perihelion will fall in February, then March, and eventually in July, meaning Earth will be closest to the Sun during Northern Hemisphere summer instead of winter.
This slow shift is one of the Milankovitch cycles, a set of orbital variations that influence Earth’s climate over tens of thousands of years. When perihelion aligns with a hemisphere’s summer, that hemisphere receives slightly more intense sunlight during its warm season. The effect is subtle on human timescales but significant enough to play a role in the timing of ice ages when combined with other orbital changes.
When Earth Reaches Perihelion
Earth’s perihelion occurs in early January each year, though the exact date and time shift slightly. In 2024, perihelion fell on January 2. In 2026, it will occur on January 3 at approximately 17:15 UTC (12:15 p.m. Eastern). At that moment, Earth will be roughly 91.4 million miles from the Sun, compared to about 94.5 million miles at aphelion six months later.
That difference of about 3.1 million miles represents Earth’s perihelion distance of approximately 0.983 astronomical units (AU), where 1 AU is the average Earth-Sun distance. It’s a small but real variation that affects the total solar energy reaching our planet, even if it isn’t enough to override axial tilt in determining the seasons.
Perihelion Across the Solar System
Every planet has its own perihelion distance, determined by its average orbital distance and how elliptical its orbit is. Mercury, the innermost planet, orbits at roughly 0.39 AU from the Sun and has a noticeably eccentric (elongated) orbit, so its perihelion and aphelion distances differ considerably. Venus orbits at about 0.72 AU with a nearly circular path, making its perihelion and aphelion almost identical. Mars, at 1.52 AU, has a more eccentric orbit than Earth, so its distance from the Sun varies enough to produce noticeable differences in solar heating between its perihelion and aphelion.
The gas and ice giants orbit much farther out. Jupiter’s average distance is 5.2 AU, Saturn’s is 9.54 AU, Uranus sits at 19.2 AU, and Neptune orbits at about 30 AU. For these distant worlds, even a relatively eccentric orbit translates to a perihelion that’s only modestly different from their average distance in percentage terms, though the absolute numbers in miles are staggering.
The concept also applies to any object orbiting the Sun. Comets often have extremely elongated orbits, giving them perihelion passages that bring them close enough to the Sun to develop their characteristic glowing tails, followed by aphelion points so distant they spend centuries in cold darkness. For asteroids, knowing the perihelion distance helps scientists determine whether an object’s orbit crosses Earth’s path, which is central to tracking potential impact hazards.