Pronunciation: (per"u-hē'lē-un, -hēl'yun), [key]
—pl. -he•li•aPronunciation: (-hē'lē-u, -hēl'yu). [key] Astron.
the point in the orbit of a planet or comet at which it is nearest to the sun. Cf. aphelion. See diag. under aphelion.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.