libration.

A periodic rocking or oscillation, especially one that changes how much of a moon’s surface is visible.

Use it for

Words that belong together

• lunar libration
• libration angle

On the page

Lunar libration revealed more of the moon’s edge.

The observer measured the libration angle.

Usage notes

Primary category: sci-fi. Forms: Usually uncountable. Legacy lexical fields mirror sense 1 only. Use numbered sense fields for all meanings.