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Here’s a brief history of Halloween full moons in Boston 🌕

A full moon in Plymouth.
A full moon in Plymouth.John Tlumacki/Globe Staff

Well, we have quite a bit of weather coming up over the next few days, with rain showers and even the chance of some first snowflakes from the remnants of a hurricane. The year 2020 has brought a lot of unusual things, but this one is kind of fun! We are going to have a full moon on Halloween, and technically for those of us on the East Coast, it’s for the first time in many of our lifetimes. Yes, indeed in Boston, the last full moon on Halloween was way back in 1955. Another bonus, Saturday’s moon is also a “blue moon,” the second full moon of the month. The next blue moon will be in August 2023.

If you do a few Google searches as to Halloween full moons you’re going to find some places where it says a Halloween full moon happened in 2001. That is still 19 years ago, so it’s fairly rare. The 2001 Halloween full moon was a fact for some, but here in Boston it technically wasn’t full on Halloween. We have to go back to 1955 to find an official Halloween full moon. Here’s why it wasn’t a full moon back in 2001 in Boston on Halloween.

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Like many things astronomical there’s a specific time when a certain phenomenon occurs. With an eclipse there’s the time of maximum darkness. Sunrise has a specific time and a specific definition, as does sunset. So when it comes to the full moon back in 2001, it occurred at what was actually officially 12:41 a.m. on Nov. 1, Eastern Standard Time. (This was prior to having pushed daylight saving time into November.)

Full moon data from 2001 and 1955 shows why in 2001, Boston didn't technically have a full moon on Halloween.
Full moon data from 2001 and 1955 shows why in 2001, Boston didn't technically have a full moon on Halloween.Astropixels.com

Therefore, technically, the moon was not full when it rose on Halloween 2001 here in Boston. It would have been full however on Halloween in Chicago, Denver, and Los Angeles. Therefore, you have to go back to 1955 to find a full moon on Halloween on the East Coast. A side note, there was a full moon on Oct. 2nd that year, and the Halloween full moon was also a blue one.

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Folks hadn’t waited that long since the last Halloween full moon either. There was also a full moon on Halloween just 11 years earlier in 1944, and that year also had a blue moon on Halloween.

There’s actually two definitions for a blue moon. The original definition had to do with getting a fourth full moon in a season. Since seasons are three months long, if you got four full moons it was considered a blue moon, but over the past decades that definition has been lost and we now think of a blue moon as the second one in a  calendar month.

The Moon will be full just before 11 a.m. on Halloween and rise that evening at just about 6 p.m.
The Moon will be full just before 11 a.m. on Halloween and rise that evening at just about 6 p.m.TimeandDate

Now, with all the weather the next few days, will you be able to see this Halloween full moon? Although it’s going to be cold on Halloween, the weather should be clear, allowing us to view the moon and illuminate the countryside. You’ll need to bundle up, though – temperatures by sunset, the final one under daylight saving time this year, will be in the 30s for many of us.

Cold weather is in the forecast for Halloween with predicted temperatures in the 30s around dark.
Cold weather is in the forecast for Halloween with predicted temperatures in the 30s around dark.WeatherBell

Follow Dave Epstein @growingwisdom.