What Time Is It?
Last updated 3/22/2022 at 11:02am
Here we are at that magical time of year when I encounter a surprising number of people who believe that we lose an hour by resetting our clocks forward from "standard" time to "daylight saving" or "summer" time. It's a ritual many of us go through twice a year, but trust me, folks: It doesn't alter the length of our day by even one second.
This whole time business, however, can be quite befuddling because not everyone observes this change. Perhaps a look at how we measure time would help resolve some of the misconceptions.
We all know that the Earth rotates on its axis and that it's this rotation that causes the sun to appear to rise in the east, drift across the sky and set in the west. If the sun shines in our sky, it can't also be in the sky on the other side of the planet. Modern technology frequently shows this to be true; we can watch a live news report from Ukraine, for example, where the sky is dark, but outside our windows in the U.S. it's broad daylight.
Our measurement of time is maintained by hundreds 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 the time, you'd go check out the clock on the local church steeple. If you traveled or communicated across greater distances you would have had a serious problem. Such long-distance travel wasn't a major issue for most back then, but it sure became one as transportation technology improved.
So, to help keep schedules straight, the railroads in the U.S. and Canada split the North American continent into time zones on Nov. 18, 1883. And, though this system was 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, U.S. law established the Standard Time Act, which not only set time zones across the U.S. but established daylight saving time (DST) – 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 might seem, for 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 Daylight Time (EST), for example, is four hours behind UT. In other words, UT minus four equals EST. So, if UT is 11, it's only 7 a.m. in New York. And on the West Coast, it's 4 a.m. Unless, of course, it's standard time.
So, what the heck time is it anyway?
Well, that all depends...