Definition:Time/Unit/Day
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Definition
The day is a derived unit of time, based on the period of rotation of Earth about its axis.
In common parlance, this equates to the mean solar day.
Conversion Factors
| \(\ds \) | \(\) | \(\ds 1\) | mean solar day | |||||||||||
| \(\ds \) | \(=\) | \(\ds 24\) | hours | |||||||||||
| \(\ds \) | \(=\) | \(\ds 60 \times 24\) | \(\ds = 1440\) | minutes | ||||||||||
| \(\ds \) | \(=\) | \(\ds 60 \times 60 \times 24\) | \(\ds = 86\, 400\) | seconds |
Symbol
The symbol for the day is $\mathrm {day}$ or $\mathrm d$.
Also known as
The day as defined here can be referred to as a solar day, in order to distinguish it from the sidereal day.
Also see
Historical Note
Until $1967$, when the second was redefined to be the SI base unit of time, the day was the fundamental unit of time.
It was defined as being the length of time it takes the Earth to rotate once on its axis relative to the sun.
Sources
- 1986: David Wells: Curious and Interesting Numbers ... (previous) ... (next): $24$
- 1997: David Wells: Curious and Interesting Numbers (2nd ed.) ... (previous) ... (next): $24$
- 1998: David Nelson: The Penguin Dictionary of Mathematics (2nd ed.) ... (previous) ... (next): day
- 2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) ... (previous) ... (next): day