Friday, June 29, 2007

Once in a blue moon

Tomorrow night there will be a full moon, the second in June.

Due to the slight discrepancy between the lunar and solar cycles, every two to three years, there are thirteen full moons in the year rather than the usual twelve. Consequently one of those full moons has to come in a month that has already had one, and that, so the know-alls say, is a blue moon.

But like most know-alls, they're wrong.

A blue moon is actually rather more complicated. Splitting the year up into the four seasons - winter, spring, summer and autumn - there are usually three full moons in each. In the olden days, these full moons had names; harvest moon in autumn and hunter's moon after it; the milk moon, hay moon and old moon. There is also the Lenten moon, which is the last full moon of winter, and as its name implies appears during lent. The egg moon (otherwise known as Easter or Paschal moon) has to appear in the week before Easter and is considered the first full moon of spring. In short, each full moon had a name relevant to the time during the seasons that it appears.

But when a second full moon appears in a month, confusion abounds. The names get out of kilter and there aren't enough to go around. So the spare full moon is called a blue moon, and traditionally it is the third full moon appearing in a season that has four full moons.

The moon that appeared on the 2nd of June was still in spring - the Flower moon. Tomorrow night's full moon is the first of summer - which makes it the Hay moon. So it's not a blue moon. There will be two more full moons before the Autumnal equinox on September 23rd - traditionally the end of summer and beginning of autumn. So this season won't have a blue moon.

The real blue moon will be the third of four that occur in the period between the Autumnal equinox and Yule, or midwinter - which is actually November 24th.

Just thought you'd like to know.

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