Time zone guides and explainers

Long-form answers to the questions the calculators can't: why time zones exist, why they don't line up with the 15° lines you'd expect, and what actually happens to your body — and your calendar — when you cross a lot of them at once.

• The history of time zones

  How the railways and the 1884 Prime Meridian Conference gave the world standard time.

• UTC vs GMT: what's actually different

  Why both names survive, what genuinely separates them, and which to use when it matters.

• The politics of daylight saving time

  Why some countries spring forward every year while most of Africa and Asia never bother.

• The International Date Line

  How a zig-zagging line in the Pacific lets you fly west and land "a day ahead".

• Jet lag: circadian misalignment and how to beat it

  The science of why crossing time zones wrecks your body clock — and what actually helps.

• The world's strangest time zone offsets

  Nepal's +5:45, the Chatham Islands' +12:45 and Kiribati's leap across the date line.

• Why China runs on a single time zone

  One country, five geographic zones, one clock — and what that means at sunrise in Kashgar.

• The countries that span the most time zones

  France, the United States, Russia and the UK — and why overseas territories settle the contest.

• How air travel handles time zones and the date line

  Why your boarding pass shows local times, and what really happens on a date-line crossing.

• How to schedule meetings across time zones

  Finding a fair working-hours overlap, when to switch to async, and why a recurring slot drifts twice a year.

• What is UTC, and why the internet runs on it

  The world's reference clock that every time zone is measured from — what it is, how it differs from GMT, and why servers store it.

• How to find the best time to call another country

  The best time is the overlap of both sides' waking hours — how to find it, and the weekend and daylight-saving traps.