Blue Moon Facts

In recent years, people have been using the name Blue Moon for the second of the two full moons in a single calendar month.

- Sapna Ranka Chheda

For a blue moon to occur, the first of the full moons must appear at or near the beginning of the month so that the second will fall within the same month.

Two full moons in one month may occur in any month out of the year except for February, which is shorter than the lunar cycle. There was a full moon on July 2, 2015. There was another full moon on July 31, 2015. So the July 31, 2015, full moon was called a Blue Moon.

However, the rare phenomenon of Two Blue Moons, occurring in the same year happens approximately once every 19 years. The months of the double blue moons are almost always January and March. For January and March to each have two full moons, it's necessary for February, the month which falls in between, to have no full moons at all.