LAHORE, Aug 31: The world had the privilege to see a ‘blue moon’ when the second full moon in August graced the sky on Friday night.

Blue moon is defined as “the second full moon in a month”. The first occurred on Aug 2. The next will take place after three years — on July 31, 2015.

The rarity of the phenomenon has given rise to the idiom, “once in a blue moon”, which means something which does not happen very often. A ‘blue moon’ has nothing to do with the colour, although the earth’s nearest neighbour can assume a bluish tinge if there is volcanic ash in the atmosphere.