Every one hour time zone, if you remember the geography lessons at school, coincides with fifteen degrees of longitude. But in practice of course governments decide how our clocks should be set and time is thus as much a political as an astronomical matter. So after the 1949 Revolution in China, the five time zones in mainland China were merged to create a single time zone — a nice example of political will trying to defy astronomical reality.

Mainland Europe has six time zones. Throw in the Azores and there is yet one more time zone for Europe, making seven in all.