Chapter 09 — Big & Curious
How do time zones work?
The earth rotates 15° per hour, so each hour-wide stripe is one time zone — in theory. In practice, political borders bend them: India is on a single zone offset by 30 minutes, China spans five geographic zones but uses one. The reference is UTC; everything else is an offset from it.
Follow-up questions
What is UTC?
Coordinated Universal Time — the modern successor to GMT, kept by atomic clocks. The world's master clock, technically.
Why do we have daylight saving time?
An early-20th-century energy-saving idea. Modern evidence says it saves little energy and disrupts sleep; many countries are debating ending it.
How do I plan a meeting across time zones?
Use UTC as the anchor, name the city not the offset ('3 p.m. London'), and double-check the week of — DST shifts don't happen on the same date everywhere.
Why does daylight saving time exist?
Originally to save energy by aligning waking hours with daylight. Modern research suggests the energy savings are minimal and the health costs (sleep disruption, more accidents the Monday after) are real.
What's UTC?
Coordinated Universal Time — the global reference clock, essentially GMT without daylight saving. Every other time zone is expressed as an offset from UTC.
Why is the date line zig-zagged?
It bends around island nations so neighbouring islands aren't on different calendar days. Kiribati famously moved the line in 1995 to put its whole territory on the same date.
Why does daylight saving still exist?
Habit and lobbying. The health and economic evidence points to permanent standard time as best; standardization is politically hard.
What's UTC vs GMT?
Functionally identical for civil time; UTC is the atomic-clock version. GMT is a specific time zone (London in winter).
Best way to schedule across zones?
Google Calendar 'World Clock' or timeanddate.com — never do the math in your head.
Why doesn't the ISS have a time zone?
It uses UTC as an operational compromise since it orbits Earth every 90 minutes and passes through all zones.
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