How rare is a Halloween blue moon?

We last saw a full moon on Halloween in 1955 and wont see it again until 2039, but how rare is a blue moon on Halloween?

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The full moon and the Hubble Space Telescope
Tony Rice
, NASA Ambassador

The Moon turns full on Saturday, October 31, 2020 at 10:49 a.m., the second of the calendar month (the other being on Thu October 1 at 5:05 pm). Making for a full Halloween blue Moon.

But is this rare? Yes, and no.

This illustration shows the Hubble Space Telescope superimposed on an image of the Moon, seen during a lunar eclipse. Taking advantage of a total lunar eclipse in January 2019, astronomers using NASA's Hubble Space Telescope have detected ozone in Earth's atmosphere. This method serves as a proxy for how they will observe Earth-like planets transiting in front of other stars in search of life. Our planet's perfect alignment with the Sun and Moon during a total lunar eclipse mimics the geometry of a transiting terrestrial planet with its star. In a new study, Hubble did not look at Earth directly. Instead, astronomers used the Moon as a mirror that reflects the sunlight transmitted through Earth's atmosphere, which was then captured by Hubble. This is the first time a total lunar eclipse was captured at ultraviolet wavelengths and from a space telescope. Credits: M. Kornmesser (ESA/Hubble), NASA, and ESA

Halloween full Moons

While the phrase "once in a blue Moon" has come to mean something that doesn't happen often, astronomically speaking blue Moons themselves aren't that rare. They occur about every 2.4 years on average.

But a full Moon landing October 31, that's much rarer. The Moon last reach full peaked here in the eastern timezone on an October 31 back in 1955.

If you are remembering one from 2001, we got close, but technically it turned full at 12:41 a.m. on Nov 1, so only a Halloween full Moon west of the eastern time zone.

The last time the Moon reached full p hase from coast to coast was back in 1944.

Looking between 1900 and 2100, the moon turns full just 10 times on October 31 somewhere in the United States.

This will next happen in 2039.

year Eastern Central Mountain Pacific 1906 11:45 pm 10:45pm 9:45 pm 8:45 pm 1925 12:16 pm 11:16 pm 10:16 pm 9:16 pm 1944 9:35 am 8:35 am 7:35 am 6:35 am 1955 1:03 am 12:03 am 2001 11:41 pm 10:41 pm 9:41 pm 2020 10:49 am 9:49 am 8:49 am 7:49 am 2039 5:36 pm 4:36 pm 3:36 pm 2:36 pm 2058 7:54 am 6:54 am 5:54 am 4:54 am 2077 5:37 am 4:37 am 3:47 am 2:47am 2096 6:17 am 5:17 am 4:17 am 3:36 am

How many Halloween full Moons are blue?

All of them.

The word "month" comes from Moon because it cycles through its phases every 29 days 12 hours 44 minutes, also known as the Moon's synodic period).  This gives us a single full Moon most months.

When a full Moon falls on the first of the month, or early on the 2nd, another full Moon is possible in months with 30 or more days (sorry February).

Since Halloween always falls on the 31st, any Halloween full Moon is a blue Moon.

International Observe the Moon Night

NASA has chosen Saturday, September 26 for the 2020 International Observe the Moon Night. Events are virtual this year but provide the opportunity to connect with enthusiasts in places like India, Iraq, and South Korea as well as the United States.

NASA, including the Lunar Reconnaissance Orbiter mission team, encourage everyone not only to take part in observations but also learn about lunar science and exploration as well as cultural connections.

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