Halloween 2020 will be really special - there will be a rare blue full moon in the sky!
When we think of Halloween, many of us conjure up terrifying images of werewolves, goblins, zombies, and other scary creatures of the night, illuminated by an eerie full moon. But how often is there a full moon in the sky on Halloween? It's obviously about a very rare occurrence! The last full Halloween Moon to appear in all time zones was in 1944 (in 2001 it appeared in the Central and Pacific time zones)!
What is a Blue Moon?
For more than half a century it has been held that when two full moons appear in one month (which happens on average every two and a half or three years), the second Moon is baptized as the "Blue Moon". So when you look up at the sky on Halloween, the Moon won't be blue, but you'll definitely be looking at something quite unusual. Full Moon for Halloween 2020 namely happens approximately once every 19 years – it is a pattern known as the metonic cycle.
This well-known lunar cycle is said to have been discovered in 432 BC Greek Meton of Athens. He found that after 19 years the phases of the Moon repeat themselves on the same date. But that's not how they know it. Due to slight changes in the Moon's cycle period and the number of leap days that intervene in the 19-year time period, the metonic cycle is not precise. For the Halloween Full Moon, the Metonic Cycle worked well in the early 20th century - between 1925 and 1944. Then the Full Moon date moved to November 1st, and in 2020 it returns to October 31st. Something rare indeed!
Interesting fact: whenever the Moon is technically full on October 31st (as it will be this year), there will also be a Blue Moon, since the lunar cycle is 29.5 days long. There is another definition of a "blue moon" - when there are four full moons in one season, the third is considered a blue moon.
When is the next Halloween Full Moon?
According to astronomers, everyone in the world will see a 100 percent full Halloween Moon for years to come 2039, 2058, 2077, 2096, etc. (19-year sample). The good news is that even if the Moon is a day or two away from its 100% fullness, it can still serve as a spooky backdrop for Halloween, since most people can't tell the difference between a 98% Full Moon and a 100% Full Moon ( for example, 2 November 2029 and 30 October 2031).
