Blue Moon over Haleiwa Surf

Here is a photo taken from inside our unit directly over the birthing rock almost due west at about 4:30am on Dec. 30, 2009

What is a Blue Moon?There are in fact two definitions for a blue moon. According to the more recent definition, a blue moon is the second full moon in a calendar month. For a blue moon to occur, the first of the full moons must appear at or near the beginning of the month so that the second will fall within the same month (the average span between two moons is 29.5 days).

How Often Does a Blue Moon Occur?
Over the next 20 years there will be about 15 blue moons, with an almost equal number of both types of blue moons occurring. No blue moon of any kind will occur in the years 2011, 2014, and 2017.

The more recent phenomenon, where the blue moon is considered to be the second full moon in a calendar month, last occurred on May 31, 2007. Two full moons in one month may occur in any month out of the year except for February, which is shorter than the lunar cycle.

The other, older blue moon event, which happens when there are four full moons in a season, last occured in August 2005. Since this type of blue moon is reckoned according to the seasons, it can only occur in February, May, August, or November, about a month before the equinox or the solstice.

Twice in a Blue Moon
The rare phenomenon of two blue moons (using the more recent definitition) occurring in the same year happens approximately once every 19 years. 1999 was the last time a blue moon appeared twice, in January and March.

The months of the double blue moons are almost always January and March. That is because the short month that falls in between them, February, is a key ingredient in this once-every-19-year phenomenon. For January and March to each have two full moons, it's necessary for February to have none at all. Since February is usually 28 days long, and the average span between full moons is 29.5 days, if a full moon occurs at the end of January, it's possible for the next full moon to skip February entirely and fall in the beginning of March.

Once in a Blue Moon
"Blue moon" appears to have been a colloquial expression long before it developed its calendrical senses. According to the Oxford English Dictionary, the first reference to a blue moon comes from a proverb recorded in 1528:

If they say the moon is blue,
We must believe that it is true.
Saying the moon was blue was equivalent to saying the moon was made of green (or cream) cheese; it indicated an obvious absurdity. In the 19th century, the phrase until a blue moon developed, meaning "never." The phrase, once in a blue moon today has come to mean "every now and then" or "rarely"—whether it gained that meaning through association with the lunar event remains uncertain.

The circumference of the moon is 6,790 lin. miles. Look how large that crater is and how far out the splash lines are! they must stretch almost 1,500 miles in each direction from the center of that crater. There are about 3,300 miles across the U.S. So that's almost all the way across the United States.


How far is the moon from the Earth?Since the moon's orbit is elliptical (oval-shaped), its distance varies from about 221,463 miles (356,334 kilometers) at perigee (closest approach to Earth) to 251,968 miles (405,503 kilometers) at apogee (farthest point). The average distance from the moon to the Earth is 238,857 miles (384,392 kilometers).