19668

Clock time has long been out of step with the heavens. Since the adoption of time zones in the 19th century, we have accepted disparities of as much as 30 minutes at the edges of the time zones (more in some cases since time zones are set by politics, not geography). And of course, the 20th century brought daylight savings time, under which most Americans accept a 1-hour disparity between April and October. While I don’t like the idea of abandoning leap seconds altogether, I don’t think it’s unreasonable to let the disparity build up to an hour before making a correction.

Michael A. Zachary
Phoenix, Ariz.

A simple solution might be to keep a running tally of time beginning, say, at midnight on Jan. 1, 2000. Like the Julian calendar that simply counts days from a zero year, a millennial clock could count seconds from the millennial year. This way, a calculation could be made, accounting for any added leap seconds, to get the local time. Since only the algorithm would change from year to year, those who rely on precision atomic time would not be affected by adding leap seconds.

Dave Heiden
Stratford, Conn.

The main reason for the nearly annual adjustment we need now is a mismatch between the definition of the second in terms of atomic time and that in terms of the average speed of the Earth’s rotation. The period for which the latter calibration was made happened to be an exceptionally fast one. If a more representative mean rotation had been used, we would need no adjustment most years, and there would be as many lost seconds as leap seconds.

Frederick Fallon
Bowie Md.

Although changing the official definition of the length of the second is a possibility, “the current length of the second is embedded in the definition of physical standards and [a change] would have very far-reaching consequences that make this option unattractive,” says Dennis D. McCarthy of the U.S. Naval Observatory. He adds that the second would still have to be redefined in the future to keep up with the Earth’s deceleration .—R. Cowen