Blue Moon Rises Tonight
July 31, 2004
Saturday
Ketchikan, Alaska - When the moon rises in the sky tonight, you
can watch a phenomena that rarely occurs. According to modern
folklore although tonight's full moon will look like an ordinary
full moon, it will actually be a bit extraordinary - a Blue Moon.
But will it really be blue? Probably not. The moon tonight as
viewed in Ketchikan should be pearly-gray, as usual.
The moon over mountains
around Ketchikan appears almost full Thursday evening.
Photograph by Carl Thompson
According to NASA,
the key to the moon actually appearing the color blue is having
lots of particles in the air slightly wider than the wavelength
of red light (0.7 micron) - and no other sizes present. This
is rare, but volcanoes sometimes spit out such clouds, as do
forest fires. With wildfires burning on July 31st in the western
U.S. and Alaska, if any of those fires produce ash or oily-smoke
containing lots of 1-micron particles, the Blue Moon could be
blue.
For a Blue Moon to occur, the
first of the two full moons that fall within a month must appear
at or near the beginning of the month so that the second will
fall within the same month. Since there are roughly 29.5 days
between full moons, it is unusual for two full moons to occur
in a 30 or 31 day month. The first full moon in July was on the
2nd and the second full moon - the Blue Moon - will be tonight,
July 31st.
The last Blue Moon happened
in November 2001. In 1999, there were two blue moon occurrences
- January 31st and March 31st. The next blue moon will appear
on June 30th of 2007. On average, there will be 41 months that
have two full moons in every century, so you could say that "once
in a Blue Moon" actually means once every two-and-a-half
years.
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