This whole business can, however, be quite befuddling, as not everyone observes this change. Perhaps a look at how we measure time would help clear up some of the misconceptions.
Our measurement of time is maintained by a number of precise atomic clocks around the world, but this wasn’t always so. Back in the 19th century, for example, time was purely a local matter. If you wanted to know what time it was, you’d go to check out the clock on the local church steeple. If you traveled or communicated across greater distances, you had a serious problem. This wasn’t a big issue for most people back then, but it sure became one as technology improved.
So to help keep schedules straight, the railroads in the U.S. and Canada split the continent into time zones on Nov. 18, 1883. And though this was an idea not immediately embraced, its practicality soon became clear.
Then came daylight saving time. It was none other than Benjamin Franklin who first conceived of this scheme in a 1784 essay, but more than a century passed before it became reality in the U.S. On March 19, 1918, the U.S. passed into law the Standard Time Act, which not only set time zones across the U.S., but also established daylight saving time — a concept that still isn’t accepted by all states.
For those who do, however, DST begins on the second Sunday in March and ends on the first Sunday in November.
As complex as time seems, to astronomers, it’s relatively straightforward. By convention, we use one time zone — that of Greenwich, England. We call this time Universal Time, or simply UT. And if you know how many time zones you lie east or west of Greenwich, you can use basic arithmetic to calculate your corresponding local time.
Each zone west of Greenwich represents a time of one hour earlier. Eastern Standard Time, for example, is five hours behind UT. In other words, UT minus 5 = EST. So if UT is 11 a.m., it’s only 6 a.m. in New York and 3 a.m on the West Coast — unless, of course, it’s daylight saving time.