Blue Moon- Is it really Blue ?

"Blue moon" is a quirky astronomical term used to describe the second full moon in a calendar month, an event which occurs only once every two and a half years.
But it hasn't always been this way.

Up until the 1940s, the term blue moon was used to describe the third full moon in a season.
In 1946, Sky & Telescope magazine mistakenly attributed it to the second full month of the month.

The error was repeated in a 1980 episode of a popular US radio show called Star Date, which in turn appeared as the answer to a question in the board game Trivial Pursuit. As a result, the mistake has stuck.

However you define it, a blue moon isn't a common event. On average they occur once every two and a half years, which probably led to the term 'once in a blue moon'.

So if the moon doesn't change colour, why use the term 'blue'?

Geoff Wyatt, Manager of the Sydney Observatory, believes it probably has more to do with how the moon might 'feel', rather than its colour.
"To have two full moons in a month, means (the Moon) has used some energy so it will be down. It's not a colour reference, it's more an emotive reference," Wyatt says.

Link:http://news.ninemsn.com.au/article.aspx?id=274991
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