Sky watchers are in for a treat with May's second full moon, known as a Blue Moon. This rare event occurs every two or three years. But why do some months have two full moons, and when can you see it in the UK? A Blue Moon is a rare event that occurs when there are four full moons in a season, with the third full moon being called a Blue Moon. However, the term Blue Moon also refers to a rare event that occurs every two or three years. The Earth takes a year to orbit the Sun, and the Moon takes 29.5 days to orbit the Earth. This means that 12 full moon cycles take 354 days, which is less than the 365 days in a calendar year. As a result, every two or three years, there is an extra full moon, resulting in two full moons in one month. The last Blue Moon was seen in 2024, and the next one will be visible on May 31st at 09:45. This Blue Moon is also known as a micro moon, which occurs when the Moon is at its farthest point from the Earth, making it appear smaller and less bright.