precession
precession — noun
1. a gradual change in the direction of a planet's or star's spin axis as the body
a gradual change in the direction of a planet's or star's spin axis as the body travels through space around another body
The textbook explains how Earth's precession changes the night sky over centuries.
Earth's precession in astronomy
Because of precession, the pole star is not always the same star.
A museum video shows precession as the planet's axis slowly shifts.
Scientists measure precession to predict where the equinox points will move.
- axial drift
a plain-language description, not the fixed scientific term
- wobble
broader and less precise than the astronomical sense
用法筆記
Used for long-term changes in the axes of planets or stars. Distinguish from sense 2, which is about the visible wobbling motion of a spinning object such as a top or gyroscope.
2. a movement where a spinning object's line of rotation slowly circles another lin
a movement where a spinning object's line of rotation slowly circles another line, so the object appears to wobble around a cone
When the toy top slowed down, its precession became easy to see.
precession in a spinning top
The lab camera recorded the wheel's precession as it spun on its stand.
Kemi drew a cone to show the precession of the spinning disk.
Students noticed precession when the gyroscope's axis began to circle.
用法筆記
This sense is used for tops, gyroscopes, wheels, and other spinning objects. Distinguish from sense 1, which refers to the slow change in a planet's or star's axis over time.