What time is it?

Tonight we switch to daylight savings time here in the U.S. Well, most of the U.S. I once missed a meeting by an hour because I lived in Arizona which didn't use DST, but the meeting was on the Navajo Reservation which did go on DST. Or maybe the meeting was in New Mexico ... or the Hopi Reservation? I don't really remember, except that it was too complicated.

When we kept paper seismograms on a drum recorder before we went digital, we would mark the sheets with coordinated universal time (CUT) when we started and stopped the record, but we used the local date. That got to be too much when my assistants occasionally changed the paper later in the evening.

Anyway, my son was confused a few weeks ago because he thought he felt an earthquake in the Bay Area. He later found the SF Examiner reporting a regional quake at about that time. But the newspaper had mistakenly taken the reported earthquake time, in coordinated universal time, and mistaken it for local Pacific Coast time. So, the son was confused, but I straightened him out.

Most earthquake times are reported as CUT, which is essentially the same as Greenwich Mean Time, so that all seismologists will be talking about the same time when comparing data. Local media sources might report the quakes in local time. So watch out. Today, CUT is 5 hours ahead of Eastern Standard Time, but tomorrow CUT will be 4 hours ahead of Eastern Daylight Savings Time.

My source for things time is the U.S. Naval Observatory. We can read there that

Starting in 2007, daylight time begins in the United States on the second Sunday in March and ends on the first Sunday in November. On the second Sunday in March, clocks are set ahead one hour at 2:00 a.m. local standard time, which becomes 3:00 a.m. local daylight time. On the first Sunday in November, clocks are set back one hour at 2:00 a.m. local daylight time, which becomes 1:00 a.m. local standard time. These dates were established by Congress in the Energy Policy Act of 2005, Pub. L. no. 109-58, 119 Stat 594 (2005).

Yep, the dates were revised to save energy. How about driving smaller cars, everyone?

There's a nice WebExhibit on DST here.

And to get the CUT right now, click here.

So how about a little tune to make us smile while we "spring ahead" tonight and lose an hour of sleep. I heard this group during my freshman year when they were called Chicago Transit Authority. Ouch! Nice brass, guys.

Seismic time - change your watches

Earthquake information is given in UCT, coordinated universal time, which is, more or less, the same as Greenwich Mean Time. (The letters are backwards thanks to the French, which is why the abbreviation for the metric International System of units is also backwards, SI). You can read about time systems at the excellent web pages of the United States' official timekeeper, the U.S. Naval Observatory.

http://tycho.usno.navy.mil/leapsec.html

The graph above shows how many milliseconds the length of day varies from 86,400 seconds, or 24.00 hours. The length of day is now about 2 milliseconds less than it was since I graduated from college in 1972 - no wonder I always seem behind the times. What about those shorter variations in the LOD (length of day): fodder for another blog.

The Earth, like me, is slowing down, due to the braking action of the tides, by about 1.4 milliseconds per day per century on the average. This is equivalent to 1 second every 714 days. Periodically, a leap second is added to account for this. The last leap second was added at the end of 2005.

So, if 2008 was a good year for you, you're lucky, because an extra leap second will be inserted once more on December 31, 2008.