秤動ひょうどう

noun

libration; oscillation of a celestial body

Technical term in astronomy for the apparent wobbling or oscillation of a celestial body, especially the Moon, as seen from another body.

• 月つきの秤ひょう動どうによって、地ち球きゅうからは月つきの表ひょう面めんの約やく59%が見みえる。

  Due to the Moon's libration, about 59% of its surface is visible from Earth.