Don't Miss This Week's Halloween Blue Moon, The Next Will Be In 2039

The Halloween Blue Moon will be on Saturday. Just how rare will this event be?

Closing October sky events on Saturday will be a rather special full moon. Not only will it be what's called a "Blue Moon", but it's also a full moon that not lands on Halloween.

Typically, Blue Moons only come once every two or three years. The last one, NASA said in a blog, was on March 31, 2018. The fact that it will land on Halloween is even more unique, since full moons only tend to land on Halloween once every 19 years.

This is because under the Metonic cycle, the phases of the moon tend to repeat on the same days of the solar year every 19 years.

"Furthermore, these are all Blue Moons. In fact, every Halloween Full Moon is also a Blue Moon," NASA Scientific Visualization Studio (SVS) said, explaining that because of the 29.5-day lunar cycle, all Halloween full moons are preceded by an Oct. 1 or 2 full moon.

Saturday's Halloween Blue Moon will appear at exactly 9:49 a.m. EST but those who would like to catch a glimpse of it can do so on Oct. 30 and 31 since the moon will appear full on both dates.

To be clear, the term Blue Moon in this case does not mean that the moon will have a bluish hue. It is simply the term that has been used in modern folklore pertaining to the phenomenon wherein two full moons happen in a single month.

That said, there have been instances in the past when the moon had a bluish tint because of a natural catastrophes, NASA said in a feature on Blue Moons.

One such instance was in 1883 after the massive Krakatoa volcano eruption in Indonesia. As the agency explained, the explosion sent a lot of ash particles into the atmosphere, scattering the red light and causing the moon to appear bluish in color.

Similar bluish moons were also reported after the 1983 El Chicon volcano eruption in Mexico, the 1980 Mt. St. Helens eruption and the 1991 Mount Pinatubo volcano eruption in the Philippines.

Although an actual blue-tinted moon will not be the case on Saturday, it will still be an excellent opportunity to watch the Halloween Blue Moon since the next one will still be far away in 2039.