Nothing's ever easy. Take time, for example.
What time is it right now?
Time is maintained by a number of precise atomic clocks around the world. But this wasn't always so; back in the 19th century, time was purely a local matter.
Want to know what time it is? Go check out the clock on the church steeple or local jeweler's shop window. But travel or communicate across greater distances and you've got a serious problem.
So to help keep schedules straight, the railroads in the U.S. and Canada split the continent into time zones on Nov. 18, 1883.
But then there's Daylight Saving Time. Benjamin Franklin first conceived it in a 1784 essay, but more than a century passed before it became reality in the U.S. On March 19, 1918, U.S. law established the Standard Time Act, which set time zones across the U.S. and established Daylight Saving Time (DST), which begins the second Sunday in March and ends on the first Sunday in November.
For astronomers, we use one time zone -- that of Greenwich, England. We call this time UT, or "Universal Time." And if you know how many time zones you lie east or west of Greenwich, you can calculate your local time.
Each zone west of Greenwich represents a time of one hour earlier. Eastern Standard Time (EST) is 5 hours behind UT. In other words, UT minus 5 equals EST. So if UT is 11 a.m., it's 6 a.m. in New York. And on the West Coast, it's 3 a.m.