This October will witness a rare phenomenon.

Unlike every month when you witness just one full Moon, this month will witness two full Moons.

Arvind Paranjpaye, director of Nehru Planetarium, Mumbai, told news agency PTI: "When there are two full Moons in a calendar month, the second full moon is called the Blue Moon." 

"Duration of a lunar month is 29.531 days or 29 days, 12 hours, 44 minutes and 38 seconds. Therefore, to have two full Moons in a month, the first full moon should take place on 1st or 2nd of the month. This extra time accumulates over the months. After about 30 months there will be one extra full Moon in the year," Paranjpaye said.

The next Blue Moon will be on August 31, 2023.