It's once in a blue moon

New Delhi, Aug 31 (IANS) There's something everyone does once in a blue moon. If you take that idiom literally, Friday was the day to do what you do occasionally.

Thousands Friday cherished watching the "blue moon", a phenomenon when a full moon appears twice in a month.

"It is a normal full moon, except for the fact that it occurs twice in a month," says C.B. Devgan of the Science Popularisation Association Communicators and Educators (SPACE).

"The special thing about it is that it's once in two or two-and-a-half years that a full moon appears twice in a month," he says.

"It is exciting, though the moon looks the same. The fact that this is the blue moon makes it special," says Devika, a student.

However, the blue moon is not blue in colour, unless there is volcanic ash in the atmosphere.

"In 1946, a writer for "Sky and Telescope" magazine declared a blue moon to be the second full moon in a month with two of them," explains Devgan.

Some years even boast of two blue moons. This last happened in 1999, and it will occur again in 2018.