Planets · The Sun · Comets and asteroids
Perihelion
Say it: pair-ih-HEE-lee-un IPA: /ˌpɛrəˈhiliən/ noun
Perihelion: The point in an orbit around the Sun where the orbiting body comes closest to the Sun.
Orbits are ellipses, not circles, so the distance to the Sun changes through every orbit. Earth's swings between about 147 and 152 million kilometers.
- Example
- Earth passes perihelion in early January, during the Northern Hemisphere's winter.
- Why astronomers use it
- A body moves fastest at perihelion, and a comet is heated most there, which is often when it is brightest.
- Tiny cosmic connection
- Earth moves about a kilometer per second faster at perihelion than at aphelion: roughly 30.3 against 29.3 kilometers per second.
Observatory Planets The Sun Comets and asteroids
Where to check it
Written for Cool Moon Facts in its own words; the sources cover the same idea in more depth.