Understanding Time Zones: A Complete Guide
Everything you need to know about time zones, from their history to practical tips for scheduling across the globe.
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How Time Zones Work
The Earth rotates 360 degrees in 24 hours, which means it turns 15 degrees every hour. In theory, this divides the planet into 24 neat time zones, each covering 15 degrees of longitude. Coordinated Universal Time, or UTC, serves as the global reference point. Time zones east of the Prime Meridian (which runs through Greenwich, England) are ahead of UTC, while zones to the west are behind. In practice, however, time zone boundaries follow political borders rather than strict lines of longitude. Countries adjust their zones to keep entire regions or nations on the same clock, which is why the actual map of time zones looks more like a jigsaw puzzle than a series of vertical stripes.
Unusual Time Zones
Not all time zones are offset from UTC by whole hours, and some of the exceptions can catch travelers off guard.
Daylight Saving Time Complications
Daylight Saving Time, or DST, adds another layer of complexity to time zone calculations. The basic idea is simple: clocks are set forward by one hour in spring and back by one hour in autumn to make better use of evening daylight. But the implementation is anything but simple. Not all countries observe DST, and those that do often switch on different dates. When the United States springs forward on the second Sunday in March, most of Europe does not follow until the last Sunday of March. During those intervening weeks, the time difference between New York and London drops from five hours to four. Countries in the Southern Hemisphere that observe DST do so during what is winter in the Northern Hemisphere, further complicating cross-hemispheric scheduling.
Tips for Working Across Time Zones
If you regularly schedule meetings or coordinate with people in different time zones, a few practices can save you a lot of confusion.