What is a Blue Moon? Several different explanations describe this infrequent occurrence.
August 31, 2012 is the second full moon of the month. This phenomenon is known as a “Blue Moon” in current discourse. This is a rather recent formulation of the term.
Sky & Telescope magazine has traced the history of the term in at least two articles and it has even been part of the change of how the term is used.
Here is a summary of what the articles describe:
- The original usage of the term was like the modern statement “When pigs fly.” (That will happen when the moon is blue.)
- Another described an infrequent event related to volcanic eruptions. The dust ejected high into the atmosphere, can give the moon and sun a bluish hue when seen through the dust. While infrequent, blue moons do occur.
- A usage closer to the popular modern concept can be traced to the Maine Farmers’ Almanac that related the term an extra full moon during a season. Each season normally has three full moons. When a season has four, the third one is called “Blue Moon.” Historically, the full moons had season names, such as Harvest Moon, Egg Moon or Lenten Moon. Because those full moons were related to specific events related to the seasons, there came a time when a season had an extra full moon without a name; the third month in that series was named “Blue Moon,” a sort of unnamed full moon for that infrequent occurrence.
- Sky & Telescope also stated that it contributed to the popular notion with articles in 1946 and 1950 that cited the Maine Farmers’ Almanac, but added that a second full moon in a month was a “Blue Moon.” This is the term that has been popularized today.
With that written, I will put here that I will not write about this topic until the next Blue Moon and let the reader determine the usage.
November 3, 2021: Before sunrise speedy planet Mercury, the crescent moon, and the star Spica are grouped together. The trio does not appear this close together again until 2033.
October 31, 2021: There is no Halloween Full moon this year, and the phase is not close. The crescent moon is in the morning sky. Mercury is low in the east-southeast before sunrise. The planet pack – Venus, Saturn, and Jupiter – gleam in the evening sky.
October 29, 2021: Venus reaches its greatest elongation from the sun. It is in the evening sky with Jupiter and Saturn. The crescent moon and Mercury are in the eastern sky before sunrise.
October 29 – November 1, 2021: The crescent moon moves in front of the stars of Leo in the eastern sky before sunrise. Watch the moon appear lower and the phase shrink (wane) each morning. Also note that there is no Full moon on Halloween this year!
October 26, 27, and 28, 2021: During the early morning hours, the bright gibbous moon appears in front of Gemini’s stars.