Lunar Calendar

Written by Jeremy Horelick
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While the lunar calendar isn't used for accurate time-measurement in most of the Western world, it is still used in many cultures, primarily for agricultural purposes. The lunar calendar differs from the solar calendar in that it measures months by periods of "lunation," or the time it takes for the moon to complete its phasic cycle. Because lunar months can vary between 29 and 30 days, there is no normative standard by which to measure events--at least not precisely.

But the lunar calendar was effective for millennia in governing planting cycles. Farmers could tell when to plant and when to sow based on the cycles of the moon. The only problem was, a year full of lunar months didn't add up to 365.25 days, the length of a solar year. To correct for this difference, some cultures added intercalary "leap" months to stay accurate.

The Lunar Calendar Today

Given our need for accurate time-measurement in setting dates, keeping appointments, and having a common calendar, lunar cycles are largely obsolete. But they still retain a symbolic importance, especially in the Far East, where astrology is intricately interwoven with lunar phases. Anyone who's ever read a horoscope has at least nominally bought into the lunar calendar, even if it was only in jest.

The truth is, with the proper astronomical information, a lunar calendar can be every bit as accurate as its solar counterpart. But who has time to keep their eyes on moon phases when there are so many more pressing tasks? Still, some watches document the phases of the moon, more as a novelty than anything else. In fact, you can find moon phases on some of the timepieces manufactured by the world's leading watchmakers.

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