Word of the Day

: September 21, 2014

aphelion

noun a-FEEL-yun

What It Means

: the point in the path of a celestial body (such as a planet) that is farthest from the sun

aphelion in Context

The comet is predicted to reach aphelion a mere 22 years from now.

"Although this seems somewhat counter-intuitive for those of us in the northern hemisphere, Earth is actually at perihelion in early January each year, and at aphelion? in early July." - Alan Hale, Alamo Gordo News, August 14, 2014

Did You Know?

Aphelion and perihelion are troublesome terms. Which one means a planet is nearest to the sun and which means it is farthest away? An etymology lesson may help you keep those words straight. Just remember that the "ap" of aphelion derives from a Latin prefix that means "away from" (the mnemonic "'A' for 'away'" can help too); peri-, on the other hand, means "near." And how are aphelion and perihelion related to the similar-looking astronomical pair, apogee and perigee? Etymology explains again. The "helion" of aphelion and perihelion is based on the Greek word hēlios, meaning "sun," while the "gee" of apogee and perigee is based on gaia, meaning "earth." The first pair describes distance in relation to the sun, the second in relation to the earth.