Sky Lights

Try a more heavenly calender to avoid the Y2K problem

By Bob Berman|Thursday, April 01, 1999

by Bob Berman

Nervous about next year? Is the whole idea of a new millennium too much? Or is it just that large round numbers like 2000 seem scary? The solution is really quite simple: try switching calendars. Methods of counting out the days are mostly arbitrary anyway, and there's nothing magical about our system.

Hebrew reckoning, for example, says it's now the year 5759. The Japanese are celebrating 2659. And if those systems seem too capricious, mark the passage of time with something more natural, like the calendars nature produces, which are based on recurring physical phenomena.Solar and lunar eclipses, for example, repeat every 18 years and 11.33 days, an interval called a saros. The period occurs when three separate lunar cycles--the full-moon cycle of 29.5 days, the moon's close-approach-to-Earth cycle of 27.55 days, and the moon's return to the sun-Earth plane of 27.21 days--come together. The saros, all 6,581.33 days, is the common denominator of the three periods.

Or you could count in terms of three saroses, an interval of 54 years and one month, the time frame in which eclipses return to the same part of the globe. Following this pattern, the great total solar eclipse over New York City on January 24, 1925, was repeated by another in February 1979. Attractively long eclipses--more than six minutes--also recur at saros intervals, allowing eclipse chasers to plan ahead. The famous Baja and Hawaii totality of 1991 will replay 18 years later with a long eclipse over China in 2009, another long one in 2027, and then (completing the three-saros cycle) a six-minute totality in 2045 that will be the longest total solar eclipse in U.S. history. These patterns may not get media attention, but they're reliable.

Astronomers have more than saros periods with which to count. For starters, they have their own system of days. After all, it's not easy to figure out exactly how much time has elapsed between two events when all manner of irregular months and leap years intervene. So to keep tabs on the uneven pulsations of Orion's swollen star Betelgeuse, now in the southwest at nightfall, an astronomer would count in Julian days. Each Julian day uses decimals instead of hours and minutes, and each starts at noon with numbers that began on January 1, 4713 B.C. It's not exactly a catchy thing, but if you want to jump on the Julian bandwagon, set your watch to J.D. 2,451,269.0 at noon on April 1.

Astronomy lets you choose from almost limitless counting schemes. Only your imagination, the power of your telescope, and your patience will curtail the possibilities. Take Mars, for instance. It's now at its brightest of the decade, outshining everything else in the midnight sky, because its slightly elliptical orbit is bringing it closer to us. These Martian flybys recur every 26 months or so, but the really close passes recur at 15- to 17-year intervals. That pattern has so far gone unnumbered. Grab this chance to be the first on your block to name it after yourself, then adopt it as a personal calendar. Or perhaps you're a romantic who favors moonlight. On April 16 take a loved one outside, pop the cork on a bottle of champagne, and say, "Wow, can you believe this is the beginning of lunation number 944?"Stay up-to-date with the latest science discoveries -- Click here to subscribe to Discover!

Galactic SkyCharts -- maps and planet finder for various latitudes
Deepsky Atlas --maps and information from the Hawaiian Astronomical Society
BasicCelestial Phenomena website
"What'sUp inthe Sky" from Sky Publishing
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