mean solar day: meaning, definition, pronunciation and examples
C2technical, scientific, formal
Quick answer
What does “mean solar day” mean?
A 24-hour period, defined as the average time it takes for the Sun to return to the same position in the sky, used as the standard civil day.
Audio
Pronunciation
Definition
Meaning and Definition
A 24-hour period, defined as the average time it takes for the Sun to return to the same position in the sky, used as the standard civil day.
The fundamental unit of solar time in astronomy and civil life, representing the average length of an apparent solar day over a year to account for Earth's elliptical orbit and axial tilt.
Dialectal Variation
British vs American Usage
Differences
No lexical or conceptual differences; usage is identical in both scientific communities.
Connotations
Purely technical and neutral.
Frequency
Extremely low frequency in general discourse; used almost exclusively in astronomy, geodesy, timekeeping, and related technical fields.
Grammar
How to Use “mean solar day” in a Sentence
The [duration/definition/length] of a mean solar day is 24 hours.A mean solar day is [defined as/based on] the average...It differs from an apparent solar day by [a few minutes].Vocabulary
Collocations
Examples
Examples of “mean solar day” in a Sentence
noun
British English
- The mean solar day forms the basis of our civil timekeeping.
- A discrepancy of several minutes can occur between apparent and mean solar time.
American English
- Universal Time (UT1) is directly based on the mean solar day.
- The length of a mean solar day is increasing due to tidal friction.
Usage
Meaning in Context
Business
Virtually never used.
Academic
Used in astronomy, physics, geology, and engineering contexts when precise time measurement is discussed.
Everyday
Not used; replaced by the simple word 'day'.
Technical
The standard term in astronomy, navigation, and time standardisation for the 86,400-second SI day.
Vocabulary
Synonyms of “mean solar day”
Strong
Neutral
Weak
Vocabulary
Antonyms of “mean solar day”
Watch out
Common Mistakes When Using “mean solar day”
- Confusing it with 'apparent solar day'.
- Pronouncing 'mean' with a negative connotation rather than as /miːn/.
- Omitting 'solar' and just saying 'mean day', which is ambiguous.
FAQ
Frequently Asked Questions
Yes, by modern definition, a mean solar day is precisely 86,400 seconds (24 hours), which is the SI unit 'day'.
Because the Earth's orbit is elliptical and its axis is tilted, the actual solar day (apparent solar day) length varies. The 'mean' averages these variations to provide a constant unit of time.
Almost exclusively in technical fields: astronomy, advanced geography, time standardisation (e.g., defining UTC), and historical scientific texts.
UT1 is time measured by the Earth's rotation relative to the Sun (based on the mean solar day). UTC is the coordinated civil time standard, kept within 0.9 seconds of UT1 by adding 'leap seconds' when needed.
A 24-hour period, defined as the average time it takes for the Sun to return to the same position in the sky, used as the standard civil day.
Mean solar day is usually technical, scientific, formal in register.
Mean solar day: in British English it is pronounced /ˌmiːn ˌsəʊ.lə ˈdeɪ/, and in American English it is pronounced /ˌmin ˌsoʊ.lɚ ˈdeɪ/. Tap the audio buttons above to hear it.
Phrases
Idioms & Phrases
- “On a geological timescale, the mean solar day is gradually lengthening.”
Learning
Memory Aids
Mnemonic
Think MEAN as in 'average' (not nasty) + SOLAR as in 'sun' + DAY. It's the AVERAGE sun-based day.
Conceptual Metaphor
TIME IS A MEASURABLE CYCLE (the solar cycle, averaged).
Practice
Quiz
What does 'mean' signify in 'mean solar day'?