At 9.36 pm on Wednesday Aug 30 in the night sky one will see a second full moon. This will be larger than the usual moon. This month there are two full moons Aug 1 and Aug 30. This happens as the lunar cycle is of 30 days just shorter than a month.It is called a blue moon because it happens every 3-4 years. The expression once in a blue moon comes from this, but the moon is not blue, just larger and brighter than usual.