Monday, August 28, 2023

'Blue Moon' Wed. Night: Largest Full Moon of 2023


Image of a 'Blue Moon' (which was also a so-called 'Super-Moon') as it appeared during the Partial Eclipse of the Moon on 2009 December 31. According to NASA's Five Millennium Catalogue of Lunar Eclipses, a 'Blue Moon' Lunar Eclipse is the rarest type of Eclipse of the Moon, occurring only 11 times per millennium! (Image Sources:, By Codybird - Own work, CC BY-SA 3.0,

By Glenn A. Walsh
Reporting for SpaceWatchtower

“Once in a 'Blue Moon' ” will come this Wednesday evening, when a Full Moon that is called a 'Blue Moon' will be visible in the sky, weather-permitting. And, this particular 'Blue Moon' will also be considered a so-called 'Super-Moon', as it will be the closest Full Moon to the Earth, and thus the largest visible Full Moon, this year.

This week's Primary Full Moon Phase occurs on Wednesday Evening, 2023 August 30 at 9:36 p.m. Eastern Daylight Saving Time (EDT) / August 31 at 1:36 Coordinated Universal Time (UTC). Just a little earlier on Wednesday, at 12:00 Noon EDT / 16:00 UTC, the Moon reaches Lunar Perigee (making it a so-called 'Super-Moon'), the Moon's closest approach to Planet Earth for the entire year - distance Earth to the Moon: 221,941.984 statute miles / 357,181 kilometers (nearly 17,000 statute miles / 27,358.848 kilometers closer than average). According to the Association of Lunar and Planetary Observers, a so-called 'Super-Moon' appears about 8 per-cent larger than a normal Full Moon, and about 15 per-cent brighter than a normal Full Moon.

At this distance, large tides are predicted along ocean coast-lines. This could be particularly problematic for the Gulf of Mexico coast of Florida and the Atlantic Ocean coasts of Florida, Georgia, South Carolina, and North Carolina, with the impending approach of Hurricane Idalia. The Moon will exert about 48 per-cent more tidal force during the Spring Tides of August 30, compared to the tides of two weeks earlier.

The previous 'Blue Moon', which coincided with a so-called 'Super-Moon', occurred on Thursday, 2009 December 31, 2:13 p.m. Eastern Standard Time (EST) / 19:13 UTC (which also coincided with a Partial Eclipse of the Moon, which makes this a very rare event). The next 'Blue Moon', which coincides with a so-called 'Super-Moon', will occur on Saturday, 2037 January 31, 9:05:42 a.m. EST / 14:05:42 UTC.

The first Primary Full Moon Phase of this month occurred on Tuesday Afternoon, 2023 August 1 at 2:32 p.m. EDT / 18:32 UTC, which was also a so-called 'Super-Moon' and also had the prediction of large tides along ocean coast-lines. For this first Full Moon of August, Lunar Perigee occurred a little less than 12 hours later on August 2 at 2:00 a.m. EDT / 6:00 UTC - the distance between Earth and the Moon: 222,022.141 statute miles / 357,310 kilometers.

Of course the phrase, “Once in a 'Blue Moon' ”, in popular parlance has come to refer to an event that comes fairly rarely. Actually, on average, a 'Blue Moon' can occur once every 2.716 years, or once every 2 years, 8 months, and 18 days, approximately.

A 'Blue Moon' occurs due to how we define calendar seasons and calendar months. A completely different calendar system would mean that 'Blue Moon' would have to be re-defined, if 'Blue Moon' is defined at all.

Also, let us be clear that this 'Blue Moon' will not look blue in the sky. The blue color of the Rainbow, technically the blue wavelength (450 to 495 nanometers) of the Electromagnetic Spectrum, has nothing to do with a 'Blue Moon'. The only time a Full Moon Primary Phase might appear with a blue tint could be when fires or a volcanic eruption release particles, of just the right size, into the atmosphere which may scatter red light (red wavelength: 700 nanometers) thus allowing the Moon to have a more blue appearance.

There is no official, astronomical definition for a 'Blue Moon'. There are three cultural definitions of a 'Blue Moon' ---

  1. The classic definition of a 'Blue Moon' is the third Primary Full Moon Phase in a calendar season which has four Primary Full Moon Phases. Most calendar seasons have three Primary Full Moon Phases, for the three months per season.

  2. The 13th Primary Full Moon Phase in a calendar year. Such a 'Blue Moon' would also satisfy the third definition of a 'Blue Moon'.

  3. The more common definition of a 'Blue Moon' (which became the more popular definition, due to misinterpretation in the media – more on this later in this article) is the second Primary Full Moon Phase in one calendar month.

    Wednesday evening's Primary Full Moon Phase will satisfy the third definition of a 'Blue Moon', the second Primary Full Moon Phase in the month of 2023 August. It does not satisfy the first and second definitions of a 'Blue Moon', as there are only three Full Moon Primary Phases in the season of Summer in 2023: July 3 (7:39 a.m. EDT / 11:39 UTC), August 1 (2:32 p.m. EDT / 18:32 UTC), and August 30 (9:36 p.m. EDT / Aug. 31, 1:36 UTC. Interestingly, the Primary Full Moon Phase of 2009 December 31 (which was a 'Blue Moon', so-called 'Super-Moon', and a Partial Eclipse of the Moon) satisfied both the second and third definitions of a 'Blue Moon'.

For a Primary Full Moon Phase to meet the requirements for the second, more common, definition of a 'Blue Moon', the 'Blue Moon' has to occur on the 30th or 31st days of a month, and the first Full Moon has to occur on the 1st or 2nd days of the same month. Except during a Leap Year (which would be extremely rare, if possible at all), a 'Blue Moon' cannot occur in the month of February.

Native Americans, as well as other ancient peoples, used the complete orbit of the Moon to define a month, what they called a 'moon'. From the Primary New Moon Phase to the next New Moon Phase, or from the Primary Full Moon Phase to the next Full Moon Phase, would be considered one month. Some religions, such as Judaism and Islam, also use the Moon to help mark dates and times of various festivals as part of a Lunisolar Calendar for Judaism and as part of a Lunar Calendar for Islam.

The orbit of the Moon around the Earth completes one revolution, in relation to the stars and lunar phases (Sidereal Period), in 27.32 Earth days. In relation to the Sun (Synodic Period), the Moon completes one revolution in 29.53 Earth days.

Since 1933, this Synodic Period has also been known as a Lunation, when used to describe the time from one New Moon Primary Phase to the next New Moon Phase. Since gravity locks the near side of the Moon to always facing the Earth, one lunar revolution is also one lunar rotation (i.e. one Lunar Day).

The term Lunation was originally coined in 1933 by British Professor Ernest W. Brown, who had just retired from Yale University. He defined Lunation #1 as the first Primary New Moon Phase of 1923: 1923 January 16 at ~9:41 p.m. EST / January 17, 2:41 UTC; the Brown Lunation Number system was used in almanacs until 1983. In 1998, Belgian meteorologist and amateur astronomer Jean Meeus introduced a new Lunation Number system, where Lunation #0 was defined as the first Primary New Moon Phase of 2000: 2000 January 6 at ~1:14 p.m. EST / 18:14 UTC.

The third Full Moon in a season with four Full Moons was called a 'Blue Moon', so that the nicknames normally given to the three regular Full Moons of a season by the Native Americans, and later adopted by farmers who immigrated to America from Europe, could remain consistent for that particular season. In the 19th century, the Maine Farmers' Almanac started listing 'Blue Moons', as an aid to farmers.

In March of 1946, Sky and Telescope Magazine (which originated as The Sky Magazine, published by New York City's Hayden Planetarium and Pittsburgh's Buhl Planetarium) misinterpreted the classical 'Blue Moon' definition, by interpreting the 1937 Maine Farmers' Almanac as promoting eleven months with one Full Moon and one month with two Full Moons. Hence, this started the more popularly-known definition of a 'Blue Moon' being the second Full Moon in a calendar month. Deborah Byrd writing for StarDate, the daily, nationally-syndicated radio program from the University of Texas McDonald Observatory, found the 1946 misinterpretation (with no reason to believe the popular astronomy magazine would be wrong) and popularized it in their broadcast of Thursday, 1980 January 31 (a 'Blue Moon' occurred that evening at 9:21:56 p.m. EST / February 1, 2:21:56 UTC).

Is one 'Blue Moon' definition better than another? Folklorist Phillip Hiscock of Memorial University in Newfoundland wrote of the new definition in his article "Folklore of the 'Blue Moon'," for the 1993 December issue of the International Planetarium Society's quarterly journal Planetarian: "Old folklore it is not, but real folklore it is."

Native Americans had several names for the Full Moon of August, which this month referred to the first Full Moon on August 1: Sturgeon Moon, Red Moon, Grain Moon, Green Corn Moon, or simply Corn Moon. Of course, these referred to the time of year when harvesting grain or corn was beginning, the best time to catch sturgeon, or the red appearance of the Moon as it rises in the haze of late Summer.

In Earth's Southern Hemisphere which is in the middle of the Winter season, the Full Moon of August is known by the names Snow Moon, Storm Moon, Hunger Moon, and Wolf Moon.

Internet Links to Additional Information ---

Earth's Moon: Link >>>

Full Moon: Link >>>

'Blue Moon': Link >>>

Lunation Number: Link >>>

'Black Moon': Link >>>

Photograph of Waxing Crescent Moon, taken by Francis G. Graham (now Professor Emeritus of Physics, Kent State University) using the historic 10-inch Siderostat-type Refractor Telescope at the original Buhl Planetarium and Institute of Popular Science / Buhl Science Center, Pittsburgh's science and technology museum from 1939 to 1991:

Link >>>

Photographs similar to this one were compiled by Professor Graham to assist with a national research project, in the 1980s, to better map the area near the Moon's South Pole. Today, four nations (U.S., Russia, China, and India) are targeting the Moon's South Pole with space probes, looking for frozen water which may exist in craters which never see sunlight; in the last few years, attempts to reach the Moon's South Pole by Israel, Japan, and Russia were unsuccessful. Such lunar water sources could help maintain a crewed lunar base, as this water can be used for drinking (H2O), creating breathable oxygen (O2), and creating hydrogen (H2) for use as rocket fuel and use in hydrogen fuel cells to power a lunar base. Last Wednesday (2023 August 23), India successfully landed their first unmanned Lunar Lander and Rover near the Moon's South Pole. Later this decade, the United States plans landing an Artemis mission near the South Pole with astronauts, including the first woman and the first astronaut of color to land on the Moon.

Related Blog-Posts ---

Today's "Black Moon"." Wed., 2015 Feb. 18.

"'Blue Moon' Tuesday Night." Tue., 2013 Aug. 20.

Source: Glenn A. Walsh Reporting for SpaceWatchtower, a project of Friends of the Zeiss          

               Monday, 2023 August 28.

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Glenn A. Walsh, Informal Science Educator & Communicator                                                               (For more than 50 years! - Since Monday Morning, 1972 June 12):
Link >>>
Electronic Mail: < >
Project Director, Friends of the Zeiss: Link >>>
SpaceWatchtower Editor / Author: Link >>>
Formerly Astronomical Observatory Coordinator & Planetarium Lecturer, original Buhl Planetarium & Institute of Popular Science (a.k.a. Buhl Science Center), America's fifth major planetarium and Pittsburgh's science & technology museum from 1939 to 1991.
Formerly Trustee, Andrew Carnegie Free Library and Music Hall, Pittsburgh suburb of Carnegie, Pennsylvania, the fourth of only five libraries where both construction and endowment funded by famous industrialist & philanthropist Andrew Carnegie.
Author of History Web Sites on the Internet --
* Buhl Planetarium, Pittsburgh: Link >>>  Buhl Observatory: Link >>>
* Adler Planetarium, Chicago: Link >>>
* Astronomer, Educator, Optician John A. Brashear: Link >>>
* Andrew Carnegie & Carnegie Libraries: Link >>>

 * Other Walsh-Authored Blog & Web-Sites: Link >>>

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