mean sun

9.9

An imaginary sun that moves at a steady speed across the sky to measure time

noun

Specialized

: sol medio

The concept of the mean sun simplifies timekeeping by assuming a uniform movement along the celestial equator.

Examples

To calculate mean solar time, astronomers refer to the position of the mean sun rather than the actual sun.
The mean sun provides a consistent measure of time.
Unlike the mean sun, the real sun's speed varies due to the elliptical shape of Earth's orbit.
Astronomers calculate time based on the mean sun.
The concept of the mean sun helps astronomers calculate time accurately by providing a consistent reference point.
To understand time zones better, one must know that the mean sun moves along the celestial equator at a steady pace.
In daily life, schedules often rely on the position of the mean sun to ensure events happen at the right time.

Surface Forms

mean sun singular

mean suns plural

Morphology

mean + Sun

The element 'mean' (average) combined with 'Sun' does cue an abstract or averaged version of the Sun, so a learner might infer a non-literal/idealized sun. However, the precise technical sense — an imaginary sun moving uniformly used to define mean solar time — is specialized and not directly predictable from the constituent meanings alone, so full comprehension requires domain knowledge.

Etymology

Mean sun imagines a pretend sun that moves at a steady speed across the sky. People use this idea to measure 'mean solar time' because the real sun speeds up and slows down, so the mean sun gives a simple, regular time.