Friday, January 1, 2010

Blue Moons

If you live in the Western Hemisphere, New Years Eve was a blue moon. (Readers in the Eastern Hemisphere still have a month before their blue moon occurs.)

Lots of news sources (example) acknowledged the blue moon, citing that it is 'blue' because it is the second full moon of the month. There's no doubt this is a very popular answer, but its trendiness doesn't mean it is completely accurate. Blue moons have occurred on the 20th day of a month.

Fact: it takes the moon 29.5 days to go from full to full. Hmmm. There's no way a second full moon can happen in 20 days. What's going on?

The modern definition of blue moon is the result of an interpretive mistake, one made long before the Internet made the transmission of such errors immediate and widespread. The challenge is to use the Internet to track down the name of the individual who reinterpreted the definition and the year it happened.

This is a good example of how erroneous information, when picked up by a reputable source, becomes entrenched.

Good hunting!

1 comment:

Max Paulsen said...

The astronomer who made the mistake was James Hugh Pruett (1886-1955), and it happened in the Sky&Telescope magazine which issued in March 1946.