Perihelion is the point in an orbit where a body is closest to the Sun — for Earth, in early January.
Coined by Johannes Kepler in 1596 as the Modern Latin perihelium, from Greek peri ('near') + helios ('sun'); re-Greeked into English as perihelion in the 1680s — a Greek-derived scientific formation.
// Where it sits
The distance effect is real and measurable. It's just swamped by 23.5 degrees of tilt.
What it really means
Earth is at its closest to the Sun in early January. Not July. January — in the depths of the northern winter, when a substantial fraction of the planet's population is scraping ice off a windscreen.
NASA makes the point directly: the seasons are mostly caused by the axial tilt, not by Earth's elliptical orbit. If distance drove temperature, the entire Northern Hemisphere's calendar would be inverted.
What does drive them is the 23.5-degree axial tilt — which changes both how directly sunlight strikes a given hemisphere and how many hours it spends above the horizon. Tilt beats distance so decisively that the distance effect goes almost unnoticed.
But almost is the interesting part, because the difference is genuinely measurable. Earth's orbit is an ellipse: about 147.1 million km at perihelion, 152.1 million km at aphelion. That's roughly 7% more sunlight arriving in January than in July, and a Sun whose apparent disc is a little over 3% larger — visible in a side-by-side photograph, invisible to anyone standing in a January street.
The prefix pair is worth keeping, because it generalises cleanly. Peri- near, apo- far, then swap the suffix for whatever you're orbiting: perigee/apogee for Earth, periastron/apastron for another star, periapsis/apoapsis when you don't want to specify.
Where it comes from
The peri-/apo- prefix pair generalises to any primary: perigee/apogee for Earth, periastron/apastron for a star, periapsis/apoapsis generically. Change the suffix, keep the logic.
Myths & misconceptions
Earth is closest to the Sun in summer — that's why it's hot.
Exactly backwards for the Northern Hemisphere. Earth is at perihelion in January, during northern winter, and at aphelion in July. NASA puts it plainly: the seasons are caused mostly by the 23.5-degree tilt of Earth's spin axis, not by its elliptical orbit.
The distance difference is negligible, so it has no measurable effect at all.
It's small but real. Sunlight at perihelion is about 7% more intense than at aphelion, and the Sun's apparent diameter differs by a little over 3% — enough that a composite photograph shows it clearly. It just doesn't drive seasons.
Compare & contrast
Perihelion vs aphelion
The same orbit's opposite extreme, about 5 million km further out, reached in early July. The pair exists because Earth's orbit is an ellipse rather than a circle — and the eccentricity is small enough that tilt beats distance decisively.
| // | Perihelion | Aphelion |
|---|---|---|
| When | Early January | Early July |
| Distance | ~147.1m km | ~152.1m km |
| Sunlight | 7% more | 7% less |
| Northern season | Winter | Summer |
How it connects
Tell it apart
Questions people ask
- When is Earth closest to the Sun?
- Early January — around 3–4 January, at roughly 147.1 million km. Earth is furthest away in early July, at about 152.1 million km.
- If we're closest in January, why is it winter?
- Because seasons come from Earth's 23.5-degree axial tilt, which determines how directly sunlight strikes each hemisphere and how long it stays above the horizon. NASA puts it plainly: the seasons are mostly caused by the axial tilt and not by Earth's elliptical orbit — and the January perihelion is what makes that obvious. Distance is a minor factor riding on top.
- Can you see the difference?
- Yes, in a side-by-side photograph: the Sun's apparent diameter is a little over 3% larger at perihelion, and the sunlight reaching Earth is about 7% more intense.