Hour
An hour is a unit of time equal to 60 minutes or 3,600 seconds, and one twenty-fourth of a standard day.
Minute: A unit of time equal to 60 seconds and one-sixtieth of an hour. An hour contains exactly 60 minutes.
Ancient Egyptian timekeeping: The systems used in ancient Egypt to track and organize time through calendars, clocks, and astronomical observation. Egyptian practice helped establish the division of day and night into 12 parts each.
Coordinated Universal Time: The international time standard used to coordinate civil timekeeping worldwide. Civil clocks express UTC time using hours, minutes, and seconds.
Sidereal time: A timekeeping system based on Earth's rotation relative to distant stars. A sidereal day is about four minutes shorter than a solar day, so its hours track a different cycle.
Second: The SI base unit of time, defined by a specified transition frequency in cesium-133 atoms. An hour equals 3,600 seconds.
Babylonian astronomy: The systematic observation and mathematical study of celestial phenomena in ancient Babylonia. Babylonian base-60 mathematics influenced later divisions of time and angles.
Time zone: A region that uses the same standard time, usually defined by an offset from UTC. Time zones assign local clock-hour values to the same instant.
Solar time: Time measured from the apparent or mean position of the Sun in the sky. Solar time follows the Sun, unlike uniform clock hours maintained by standard time.
Day: A period of 24 hours, commonly based on one rotation of Earth relative to the Sun. The standard day is divided into 24 hours.
Sundial: An instrument that tells time from the position of a shadow cast by the Sun. Sundials made daylight hours measurable, though their length varied by season.