Ever heard the phrase "Once in a Blue Moon" to mean something that rarely occurs or happens. According to science what is it? Is a Moon really Blue when it is called a Blue Moon? No, not at all.
On July 31, 2004, a reare astrological phenomenon called the Blue Moon occurs. It is nothing but a second full moon occuring in the same calendar month. It occurs around 18:05 Greenwich Meridian Time.
Countries to the East of India cannot consider it as a Blue Moon because for those countries August 1st would have already dawned, and the full moon shall belong to the new month of August.
July 2004, had a full Moon on the 2nd and the other full moon called the Blue Moon occurs on the 31st. What a rare spectacle!! A full Moon can also be defined as the third full Moon in a season that has four full Moons.
It has been reported that there would be about 17 Blue Moons over the span of the next 20 years.
The last Blue Moon occurred on November 30, 2001. Blue Moons shall occur in the years 2005, 2007, 2008, 2009, 2010, 2012, 2013, 2015, 2016....
Some years shall have two Blue Moons. Such events occur once in 19 years.The last time this was in 1999, with a Blue Moon appearing first in January and then in the month of March.
The short month of February that comes in between these two months is the key-factor behind this occurrence.