Stargazers: What time is it? It all depends ...


Nothing's ever easy. Take time, for example. What time is it right now?

Most people simply give a quick glance at their watch to know the answer. For those of us in science, however, time often depends on several factors.

As someone who writes about upcoming astronomical events for national and international audiences, I constantly have to determine the time that a celestial event will occur in different time zones.

We all know that the Earth rotates on its axis, and that Earth's rotation causes the sun to rise in the east, drift across the sky and set in the west. If the sun shines in our sky, we know it's not shining on the other side of the planet. Modern technology has shown this to be true. We can watch a live news report happening in the Middle East, for example, when the sky is dark there, but it's broad daylight in the western United States.

So what time is it, anyway? That's a simple question with no simple answer. In mid-March, many of us change our clocks to daylight saving time, or summer time. This is even more befuddling because not everyone observes this change.

Time is maintained by a number of precise atomic clocks around the world. But this wasn't always the case. 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. But travel or communicate across greater distances, and you've got a serious problem. This wasn't a big issue for most back then, but it became one as technology improved.

So, to help keep schedules straight, American and Canadian railroads split the continent into time zones on Nov. 18, 1883. Though this idea was not immediately embraced, 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 U.S. On March 19, 1918, the U.S. government established the Standard Time Act, which set standard time zones across the U.S. and established daylight saving time — a concept that still isn't accepted by all states today.

For those that do, however, DST begins on the second Sunday in 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 Coordinated Universal Time, or UTC. If you know how many time zones 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 that's one hour earlier. Eastern Standard Time, for example, is five hours behind UTC. In other words, Coordinated Universal Time minus five hours equals Eastern Standard Time. So, if UTC is 11 a.m., it's only 6 a.m. in New York and 3 a.m. on the West Coast of the U.S. — unless, of course, it's during daylight saving time.

So, what time is it? Well, that all depends.

Visit Dennis Mammana at


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