MAX EBB in the main cabin struck six bells. I reflexively checked my cheap digital watch, which I know loses only two seconds a week because I reset it every weekend for race starts. The striking clock in the cabin was running about three minutes fast. "You know what would be really cool?" said Lee. "Don’t even use a chronometer. You could find longitude by the lunar distance method, just like Joshua Slocum. The math isn't really that hard." "Now wait a minute," said the cruiser. "We're turning the clock back to 1960, not 1760. Besides, I think they stopped publishing the tables to do lunar distance about 100 years ago." "You don't need no steenkin' tables," Lee insisted. "Just use the method of lunar position. Nothing different from, like, plotting regular old star and moon
It's not very precise, but Lee's 'Lunar Position' method can determine longitude without a chronometer.
LOPs." "You mean I can find longitude without a chronometer and without higher math?" "No, you can't find longitude without
a chronometer," I asserted. "Yes, you can," Lee taunted, "if you take a moon sight and two non-moon sights, such as star sights — as long as the moon is bearing very approximately east or west. It doesn’t work if the moon is near meridian transit." "Lee," I tried to explain patiently. "It doesn’t matter how many lines of position you have on the chart. If your chronometer is running fast, all the LOPs will be too far to the east. If your clock is running slow, they're all too far to the west. I've tried this. All the lines will still cross in the same cocked hat. The error is a quarter of a degree of longitude, or fifteen minutes of arc, for every minute of time error." "Ah, but the moon is different!" she insisted. "All the stars and planets, for
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• October, 2011
The October 2011 eBook issue of the West's premier sailing and marine magazine.