libration
/laɪˈbreɪʃən/
noun
Origin
Latin
librare — to balance, swing, or poise
Overview
Meaning Now
- A real or apparent oscillatory motion of a celestial body, such as the Moon, as viewed from another body, such as the Earth.
- A slight swaying or balancing motion.
Literal older meaning
a balancing or weighing
Language path
Latin → English
Earliest form
libratio
Earliest period
17th century
Journey
The term was popularized in astronomy during the 17th century, notably by scientists like Galileo and Hevelius, to describe the phenomenon where the Moon appears to nod or rock, revealing slightly more than 50% of its surface over time despite being tidally locked.
Evolution
- Latin
libra
“a balance, scale, or pound”
The noun base from which the verb librare is derived.
- Late Latin
libratio
“a balancing, swaying motion”
- 17th century English
libration
“balancing motion, especially in astronomy”
Adopted into technical astronomical discourse.
Connections
Word parts
libr-
root
balance
-ation
suffix
action or process
Related across languages
French
libration
Spanish
libración
libration
Explore next
Related to libration
External references use DefinedTerm semantics.