2020, October 31: Rare Halloween Full Moon

Astronomy, Sky Watching
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Halloween Art
2020: Halloween Full moon first since 1955 in Central Time Zone and since 1944 for North America. Photo Credit (https://www.publicdomainpictures.net/)

A rare Halloween Full Moon, 76 years in the making, is visible across most of the planet in 2020.

by Jeffrey L. Hunt

No, it’s not Comet Halley, but it’s been 76 years in the making, a Halloween Full Moon that is visible nearly across the entire globe.

During Halloween in 1944, a Full Moon occurred for nearly all the globe.  This was the last time a Halloween Full Moon was globally visible.

Many images of the season display cats with curved backs, leafless trees, ghosts, goblins, ravens, bats, and full moons (such as those on the accompanying graphic), but a Halloween Full Moon is a rare occurrence.

As the moon revolves through space, we view its sunlit surface in various shapes — the moon’s phases. We give them interesting names such as waxing gibbous or waning crescent.

Observers from half the globe can see the moon simultaneously. As Earth rotates and the moon rises higher into the sky. As it sets in one part of the globe, the moon rises in another part of the world.

No special equipment is needed to view this Full Moon. It is no different from any other full phase, except for the sentimentality of the date.

Because October has 31 days and a lunar cycle occurs every 29.5 days, a Halloween Full Moon means that the month’s first full moon occurs on October 1 or 2, depending on the time of the full phase.  It also marks the year’s Harvest Moon (October 1, 2020).

Because of the varied uses of the term “blue moon,” the Halloween Full Moon is the second of the month, and might be named a “Blue Halloween Full Moon.”

Many casual observers that see a bright moon might think that it’s full.  The moon might be gibbous or nearly full. Astronomically, the moon is full for an instant of time when it is opposite the sun from Earth.  During that night when the moon appears as a complete globe of light, we frequently use the “full moon” term.  Even a day before or after the actual date, the term is used.

For a reasonable discussion, let’s dig into the astronomical definition.  Further it is important to consider the observer’s location and time system (standard or daylight) that is used there.  Every place on Earth does not have the same clock time or even display the same date.  For example, during daylight time 1 p.m. in New York is 2 a.m. the next calendar day in Tokyo.  Because of the use of time zones, the fact that the earth is round, and not all places have daytime and nighttime simultaneously, tells us to make this distinction. A full moon may not occur on the same day for all earthly locations. To determine whether a Halloween Full Moon occurs, the local calendar must read October 31 and the full moon time must be from 12:00:01 a.m. to 11:59:59 p.m. local time.

Surveying U.S. Naval Observatory data from 1930 to 2050, the window occurs nearly every 19 years. Here are the Halloween Full Moons. Here is when recent Halloween Full Moons occurred:

  • 1944, October 31, 7:35 a.m. CST.  This was before Daylight Saving Time was used. The entire planet had a Halloween Full Moon
  • 1955, October 31, 12:04 a.m. CST.  There was no Halloween Full Moon for western North America and the Western Pacific to the International Date Line. All locations eastward to to the International Date Line had the Halloween Full Moon.
  • 2020, October 31, 9:49 a.m. CDT. All locations eastward to GMT+8 time zone with daylight time or GMT+9 hours with out daylight time.
  • 2039, October 31 (5:36 p.m. CST).  With the current public dislike for daylight time, the future of it is unpredictable. Standard time is used in this note.

In the Western Hemisphere, the year 2001 was a near miss for a Halloween Full Moon for North and South American time zones east of Central Time. (Daylight Time ended on October 28, 2001.) The moon was Full at 11:41 p.m. CST. One cycle earlier, in 1982, the potential Halloween Full moon occurred nearly seven hours too late (November 1, 6:57 a.m. CDT) for North America and South America.  In 1974, another near miss occurred when the full moon occurred at 7:19 p.m. CST on October 30. (Daylight Time ended October 27.)

The 2020 Halloween Full Moon is visible in North America and South America, and most of the globe, except for regions west of the International Date Line, such as Eastern and Central Australia, New Zealand, Papua New Guinea, Guam, and eastern Russia. The Halloween Full Moon occurs in all time zones eastward from the Prime Meridian through Europe, Africa, Asia, India, Indonesia, Korea, and Japan to western Australia. It occurs eastward to GMT+8 hours, with daylight time and GMT+9 hours for countires without daylight time. For regions to the east of these time zones, the Full Moon occurs there during the early morning hours of November 1. 

The next Halloween Full moon is during 2039 in North America and South America. Depending on the regional status of the use of daylight time, possibly two time zones east of the Greenwich, England meridian can witness a Halloween Full Moon. It’ll occur before Comet Halley’s return in 2061. So “celebrate” this year’s Halloween Full Moon!

(Article edited October 26, 2020)

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