The Blue-Moon articles in our March issue struck a chord with readers. We received dozens of letters from astronomy enthusiasts who, like us, felt compelled to try and figure out the Maine Farmers' Almanac's rule for Blue Moons.

From the August 1937 almanac page reproduced in Sky & Telescope, many readers correctly deduced that the Blue-Moon rule involves the seasons. Those who realized that a Blue Moon is the third of four full Moons in a season include Charlie Kluepfel, Silvio Marazzi, Bruce McCurdy, Jean Meeus, Ted Molczan, Joe Orman, Jay Respler, and Dan Tilque.

Others suggested that a Blue Moon might be the second full Moon under a given astrological sign. But we found no mention of astrology in any of the almanacs we examined. With some trepidation we acknowledge John Blaisdell, Joseph L. Gerver, Willi Kratzer, Jan N. Pedersen Jr., and Kelley L. Ross for suggesting this other way to determine Blue Moons ‹ a way we hope will not be adopted!

Two correspondents correctly predicted the date of the next Blue Moon. But Larry Molnar and Bill Petry used the apparent Sun to define the beginnings of the seasons. By coincidence, the Maine rule gives a Blue Moon on February 19, 2000, using either the mean Sun or the apparent Sun.

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