The knowledge of time
Everything time
means.
From the 9,192,631,770 atomic oscillations in one second to the political decision behind a time-zone boundary.
Time zones
What do PDT, MDT, CDT and EDT mean?
The four daylight-time abbreviations used across the contiguous United States, their UTC offsets and their standard-time partners.
Read the answer →How do time zones work?
Time zones convert one global instant into the local civil time chosen by each jurisdiction.
Read the answer →What is daylight saving time?
Why clocks move, why the date differs by country and why a city’s offset cannot be assumed year-round.
Read the answer →How does the International Date Line work?
The place where neighbouring civil time zones can carry dates one calendar day apart.
Read the answer →How time works
Why is a day 24 hours long?
Earth’s rotation gives us the day; ancient counting systems gave it 24 named hours.
Read the answer →Why are there 60 minutes in an hour?
The answer runs through Babylonian base-60 mathematics, Greek astronomy and medieval clockmaking.
Read the answer →Solar time vs clock time
Why the Sun is not always highest at 12:00 and why sunrise changes with both longitude and the calendar.
Read the answer →Standards
How does an atomic clock work?
Atomic clocks turn an invariant atomic transition into the world’s most stable tick.
Read the answer →UTC vs GMT: what is the difference?
GMT is a historic mean-solar reference and modern time-zone label; UTC is the atomic international time standard.
Read the answer →What is a leap second?
A one-second adjustment that has kept atomic civil time close to Earth’s irregular rotation.
Read the answer →History