公転(こうてん)

公転(こうてん) is the standard astronomical term for orbital revolution — one body moving around another under gravity. It is taught and used as a pair with 自転(じてん) ("rotation on the body's own axis"); Japanese science textbooks contrast the two side by side.

Forms

• 公(こう) (here functioning roughly as "public, around a center") + 転(てん) ("turn, revolve") → 公転(こうてん)

Common collocations

• 公転(こうてん)する: to revolve, to orbit
• 公転(こうてん)周期(しゅうき): orbital period
• 公転(こうてん)軌道(きどう): orbital path
• 公転(こうてん)速度(そくど): orbital speed
• 太陽(たいよう)の周(まわ)りを公転(こうてん)する: to orbit the Sun
• 地球(ちきゅう)の公転(こうてん): the Earth's revolution

CONTRAST WITH 自転(じてん):

• 自転(じてん): rotation on its own axis — produces day and night
• 公転(こうてん): revolution around another body — produces the year, the seasons (when combined with axial tilt), and the lunar month
• The two are usually introduced together; "自転(じてん)と公転(こうてん)" is essentially a fixed phrase in astronomy class.

Similar / related terms

• 軌道(きどう): orbit (the path itself, as a noun)
• 周回(しゅうかい): circling around (used for satellites, e.g., 地球(ちきゅう)を周回(しゅうかい)する)
• 回転(かいてん): rotation, turning (general, non-astronomical use)
• 太陽系(たいようけい): the solar system

Usage

• 公転(こうてん) is restricted to astronomy and physics. For "go around" in everyday contexts, 周(まわ)る or 周回(しゅうかい) is used: 湖(みずうみ)を周(まわ)る ("to go around the lake").
• The pattern is typically [orbiting body]が[central body]の周(まわ)りを公転(こうてん)する: 月(つき)が地球(ちきゅう)の周(まわ)りを公転(こうてん)する.
• Several homophones share the reading こうてん: 好転(こうてん) ("a turn for the better"), 交点(こうてん) ("point of intersection"), 荒天(こうてん) ("stormy weather"). Distinguish them by kanji and context.