NBC News - A blue moon will fall on Halloween this year, making the spookiest night of the year just a little bit eerier. On Oct. 31, there will be the second full moon of the month, which is what's commonly referred to as a "blue moon."
In the past, the definition of a blue moon was different. According to NASA, in a season with four full moons instead of three, the third full moon used to be (and sometimes still is) called “blue.” The Halloween full moon is the second of three in autumn this year.
"There is not much significance to a blue moon other than timing coincidence," Karl Gebhardt, a professor of astrophysics at the University of Texas at Austin told NBC's "TODAY."
"Since the orbit of the moon around the Earth is about 27 days, as long as the timing is good, we can get two full moons in a month," Gebhardt said. "This is what is now called a blue moon. It’s great that it is happening on Halloween! That doesn’t happen very often, but it is 2020, so all bets are off. As far as I know, having two full moons in one month has never been more or less significant as it is today."
What can you see on Halloween 2020?
A full moon occurs when the near side of the moon is completely sunlit. For the first time since 2001, a blue moon will fall on Halloween, making it a Halloween blue moon.
The moon won't actually appear to be the color blue — the moon gets its name from a 16th century folklore writer and back then, the term meant something impossible or absurd.
How rare is a blue moon?
NASA says that the moon is full on Halloween approximately every 19 years.
"In fact, every Halloween full moon is also a blue moon," NASA says. "That's because the cycle of lunar phases (the synodic month) is 29.5 days long, plus or minus a few hours, so any full moon on October 31 must be preceded by a full moon on October 1 or 2."
According to the Farmer's Almanac, this is the first full moon that falls on Halloween which will be visible in all times zones since 1944 (the one in 2001 was only visible in the Central and Pacific time zones).
What is the meaning of the blue moon in astrology?
While scientists at NASA say there is absolutely no significance to the blue moon, some astrologers have a different point of view. In an article in The New York Times, Jessica Dore, a tarot card reader said they can signify change, or set the stage for a rare event to occur.
And although it is not based in science, pop culture has led us to believe that a full moon can make people "crazed," thus the term "lunatic."
When will the blue moon appear on Halloween?
According to NASA, the moon will appear full from everywhere on Earth on Oct. 31 and will rise in the east around sunset and set in the west around sunrise. It is highest overhead in the late night and very early morning hours.
"I suggest going to the scariest place one can find and looking up at the moon,'" said Gebhardt. "It will be up all night, so anytime is good (midnight would be the most fun). I like to think about how humans have actually walked on it. It’s inspiring!"
What’s a rare moon event?
There are many different types of rare moon events, from the supermoon to the blood moon to the blue moon and the harvest moon. Blue moons are relatively rare. They occur about every 2.5 years — the last one was in March 2018.
A super blood wolf moon occurred in January 2019. That's a combination of a total lunar eclipse and a full moon. A super blue blood moon happened in 2018 and even inspired some scary baby naming trends.