WRAL WeatherCenter Blog

How rare is a Halloween blue moon?

Posted September 23, 2020 7:46 p.m. EDT
Updated October 28, 2020 6:17 p.m. EDT

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.

The full moon and the Hubble Space Telescope

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.

NASA's website also has lunar science and cultural acitivites for the whole family.

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