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Blue Moon PDF Print E-mail
Written by Steve Glennie-Smith   
Thursday, 31 December 2009 15:55

If we see it tonight, there will be a Blue Moon - which is a second full moon in the same calendar month.  Hence the phrase 'Once in a Blue Moon'.  They're not as infrequent as you might think - the last Blue Moon was on 30th June 2007, and the next will be on 31st August 2012.  Even Blue Moons on New Years Eve are not exceptionally rare - the last was on 31st December 1990, and the next will be on 31st December 2028.  This 19 year interval is known as a Metonic Cycle.

However, two other things will make this one special.  There will be a partial eclipse of the moon, which should be at its best at 19:11 - though the viewing prognosis is not good.

The other is that this week is Week 53 in the ISO 8601 date standard.  Most years only get up to Week 52 - it depends when the first Thursday of the year occurs - which in practice means it must be 1st January, as it was in 2009.  If 2nd January in a leap year is a Thursday, that year will also have 53 weeks.  There will be no more Blue Moons in Week 53 in this century or the next.

By the way, the converse - known as a Black Moon, is when there are two new moons in the same calendar month.

Having furnished you with the last bits of useless information for 2009 - have a good 2010!


Last Updated on Saturday, 09 January 2010 11:02

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