On October 31st, Blue Moon will be spotted in the sky. It is called as the Blue Moon because it is the second of two full moons to occur in a single calendar month. The last Blue Moon happened on March 3, 2018. In the year 1994, Blue Moon was spotted on Halloween day and now in 2020, it is going to be the same. According to a CNET report, for the first time since World War II, the 2020 Halloween full moon will be visible to the whole world, rather than in only a few parts of it.

According to the NASA website, a 'Blue Moon' is the second full moon in a calendar month. Generally, every month will have one full moon, but often a second sneaks in. There are two ways of calculating the date of a Blue Moon. Seasonal Blue Moon means the third Full Moon in an astronomical season with four Full Moons. Monthly Blue Moon means the second Full Moon in a month with two Full Moons. Blue Moon occurs, on average, every two and a half years.

A Blue Moon usually appears as it does on every other day, contrary to its name. A full moon's date, all by itself, does not change the colour of the moon. The moon on October 31 will, as usual, be pearly-gray. There was a time, however, not long ago, when people saw blue moons nearly every night. Full moons, half moons, crescent moons - they were all blue, except in some cases they will be green.

According to the Old Farmer's Almanac, "this full Moon name is attributed to Native Americans because it marked the time when corn was supposed to be harvested."

The original astronomical definition of a Blue Moon is the seasonal Blue Moon. For each celestial season, there are typically three full moons, which is the time between each solstice and the equinox. But in certain years, in a season, there are four full moons. When this occurs, the third Full Moon is considered as a Blue Moon.