Short answer
Aphelion is a planet’s farthest point from the Sun; perihelion is its closest. These are orbital-distance terms, not seasonal labels: Earth reaches aphelion in July and perihelion in January, despite July being summer in the Northern Hemisphere. 1 2
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At a glance
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| Question or attribute | Aphelion | Perihelion |
|---|---|---|
| Distance extreme? | Farthest from the Sun | Closest to the Sun |
| Earth reaches it when? | July | January |
| Earth–Sun distance given by NASA? | 94,500,000 miles | 91,400,000 miles |
| Does the definition specify a season? | No | No |
The distances and months describe Earth; they are not part of either term’s definition. 1 2
What each thing is
Both words identify a point along an orbital path. An orbit is a repeating path around another object, and NASA describes planetary orbits as nearly circular ellipses. Aphelion and perihelion mark the farthest and nearest Sun distances along that path, rather than naming two different kinds of orbit. 1
Key differences
The decisive difference is which distance extreme is meant: maximum for aphelion, minimum for perihelion. For Earth, NASA’s figures differ by more than 3 million miles, although that gap is small compared with the total distance to the Sun. Neither word, by itself, tells you the distance in miles. 1 2
How to tell them apart
Ask two questions: distance from what, and nearest or farthest? If the reference is the Sun, farthest means aphelion and nearest means perihelion. The limit of this rule is the reference body: for a satellite orbiting Earth, NASA uses apogee and perigee instead. A hemisphere or season is not the identification test. 1
Where they overlap
The terms share the same reference—the Sun—and can describe opposite points of the same planet’s orbit. Earth therefore has both an aphelion and a perihelion. They are complementary descriptions of its changing distance, not competing classifications of Earth or its entire orbital path. 1 2
Edge cases
An Earth-centered description can sound deceptively similar. The Moon’s farthest point from Earth is apogee, not aphelion, even though both identify a farthest point. Likewise, the Moon’s closest point to Earth is perigee. What matters is the body from which distance is being measured, not simply that Earth appears in the discussion. 1
Why the distinction exists
The vocabulary separates two opposite distance conditions without relying on a calendar or local seasonal experience. This is especially useful for Earth: its farthest-Sun point falls during Northern Hemisphere summer. NASA’s seasonal explanation instead points to Earth’s tilt, including the South Pole facing toward the Sun during Northern Hemisphere winter. 1 2
Common misconceptions
“Closest to the Sun” does not mean “Northern Hemisphere summer.” Earth’s January perihelion directly contradicts that shortcut. Nor does “nearly circular” mean the two distances are identical: NASA describes planetary orbits that way while giving distinct closest and farthest distances for Earth. Keep orbital geometry separate from seasonal labels. 1 2
Examples
Two concrete cases apply the distinction. First, Earth in July is at aphelion: its Northern Hemisphere summer does not change the farthest-distance label. Second, Earth in January is at perihelion: Northern Hemisphere winter does not change the nearest-distance label. Both cases show why the distance definition is more reliable than a seasonal association. 2