Noon depends on where you stand
Before standardised time, communities often used local time tied to the Sun. Places at different longitudes did not share exactly the same local noon. That was less troublesome when travel and communication were slow.
A practical problem
As journeys connected more places, differences between local clocks became harder to manage. A traveller might need to reconcile the time at their origin with the time at their destination. A shared reference made coordination easier.
Why Greenwich matters
Greenwich Mean Time developed from mean solar time at Greenwich. “Mean” refers to an average: apparent solar days are not all precisely equal. The Greenwich meridian became an important reference for navigation and timekeeping.
A way to picture the idea
Earth turns through roughly 360 degrees in a day. Dividing that by 24 hours gives 15 degrees per hour as a simple geometric model. Actual civil time zones do not follow a perfectly regular grid; the diagram is conceptual, not a current time-zone map.
Sources & further reading
- Royal Museums Greenwich · Time ↗
- Royal Observatory Greenwich · The astronomical basis of timekeeping ↗
Sources checked 13 November 2026. These organisations provide reference material and do not endorse this website.
