Think of the satisfaction of aiming your sextant at the moon and determining time (GMT) accurately! You can do this anywhere- at sea, in the mountains- no natural or artificial horizon is needed. This is the old method of "lunars" which was used by mariners (and explorers) to reset their clocks almost until the beginning of the 20th century.

Because the moon moves much slower across the sky than the stars, its changing position can be used in sort of a reverse process of sight reduction to find the time. The Nautical Almanac no longer has tables of precomputations for finding the time based on the distance between the moon and certain selected stars as it once did. Instead, this book can be used with the modern Nautical Almanac to find the time in this way with quick and easy computations. That is not to say, however, that making the observations are so easy. The practicing navigator will appreciate the opportunity to use the sextant in this additional way, and the challenge it presents. Even amateur astronomers may enjoy this interesting pursuit.

The present justification for celestial navigation is that it provides a backup when electronics fail. Since electromagnetic shock from a nearby lightening strike can derange timekeepers as well as electronics, the celestial solution which includes "lunars" becomes even more powerful.

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