Nothing’s ever easy. Take time, for example.
What time is it right now? Most people find that a quick glance at their wristwatch gives a sufficient answer. For those of us in science, however, the answer often depends on several factors.
When writing about upcoming astronomical events for national and international audiences, I’m constantly faced with determining the time of a celestial event where you live.
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 has shown this to be true; we can watch a live news report from the Middle East, for example, where the sky is dark, but we look out our window and see that it’s broad daylight.
So, what time is it anyway? A simple question with no simple answer. After March 8 of this year, when many of us change our clocks to daylight saving or summer time from standard, it can become even more befuddling, especially because not everyone observes this change.
Time is maintained by about 400 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. Want to know what time it is? Go check out the clock on the church steeple.
But travel or communication across greater distances created serious problems. This wasn’t a big issue for most back then, but it became one as technology improved.
So, to help keep schedules straight, the railroads in the United States and Canada split the continent into time zones on Nov. 18, 1883. And, though this was an idea not immediately embraced by all, its practicality soon became clear.
Then came daylight saving time. Benjamin Franklin first conceived of this scheme in a 1784 essay, but more than a century passed before it became reality in the United States.
On March 19, 1918, U.S. law established the Standard Time Act, which not only set time zones across the United States but also established daylight saving time — a concept that still isn’t accepted by all states.
For those that do, however, daylight saving time begins on the second Sunday of March and ends on the first Sunday in November.
As complex as time seems, it’s relatively straightforward for astronomers. By convention, we use one time zone — that of Greenwich, England. We call this time Universal Time. 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 Universal Time. In other words, Universal Time — 5 = Eastern Standard Time. So, if Universal Time is 11 a.m., it’s only 6 a.m. in New York. And on the West Coast, it’s 3 a.m. Unless, of course, it’s daylight saving time.
So, what time is it?
Well, that all depends …
— Dennis Mammana is an astronomy writer, author, lecturer and photographer working from under the clear dark skies of the Anza-Borrego Desert in the San Diego County backcountry. Contact him at mammana@skyscapes.com and follow him on Twitter: @dennismammana. The opinions expressed are his own.