Blue moon

This article is about the astronomical phenomenon. For other uses, see Blue Moon (disambiguation).
An ESA radio telescope located at the New Norcia Station, Western Australia, tracking the "super blue moon" of August 30, 2023. The blue colour is an effect of the camera.[1]

A blue moon refers either to the presence of a second full moon in a calendar month, to the third full moon in a season containing four, or to a moon that appears blue due to atmospheric effects.[2]

The calendrical meaning of "blue moon" is unconnected to the other meanings. It is often referred to as “traditional”,[3][4] but since no occurrences are known prior to 1937 it is better described as an invented tradition or “modern American folklore”.[5] The practice of designating the second full moon in a month as "blue" originated with amateur astronomer James Hugh Pruett in 1946.[6] It does not come from Native American lunar tradition, as is sometimes supposed.[7][8]

The moon - not necessarily full - can sometimes appear blue due to atmospheric emissions from large forest fires or volcanoes, though the phenomenon is rare and unpredictable (hence the saying “once in a blue moon”).[9][10][11] A calendrical blue moon (by Pruett's definition) is predictable and relatively common, happening 7 times in every 19 years (i.e. once every 2 or 3 years).[2] Calendrical blue moons occur because the time between successive full moons (approximately 29.5 days) is shorter than the average calendar month.[12] They are of no astronomical or historical significance, and are not a product of actual lunisolar timekeeping or intercalation.

  1. ^ "Chasing Chandrayaan and the super blue Moon". www.esa.int. The European Space Agency. August 31, 2023. Retrieved September 21, 2024. Note that the blue colour surrounding the Moon in these images is the result of atmospheric and camera effects. The Moon itself does not change colour.
  2. ^ a b "blue moon, n." Oxford English Dictionary. Oxford University Press. September 2023. Retrieved May 3, 2024.
  3. ^ Dobrijevic, Daisy (January 13, 2024). "Blue Moon: What is it and when is the next one?". space.com. Retrieved May 4, 2024. A seasonal Blue Moon is the traditional definition of a Blue Moon and refers to the third full moon in a season that has four full moons according to NASA.
  4. ^ Hannikainen, Diana (August 29, 2023). "The Moon is "Blue" this Wednesday... Or is it?". Sky & Telescope. Retrieved May 8, 2024. The 1937 Maine Farmer's Almanac reveals the traditional meaning of "Blue Moon."
  5. ^ "What is a blue moon? Is the moon ever really blue?". Library of Congress. September 19, 2019. Retrieved May 4, 2024. So, 'blue moon' as most of us today know it, is modern American folklore, but with a long interesting history involving calendars and the measuring of the year. Still, no matter what meaning you give it, blue moons are pretty rare, and everyone knows what you mean when you say "once in a blue moon!"
  6. ^ "What is a Blue Moon". Sky and Telescope. July 27, 2006. Retrieved May 7, 2024. Some three years later, in March 1946, an article entitled "Once in a Blue Moon" appeared in Sky & Telescope (page 3). Its author, James Hugh Pruett (1886-1955), was an amateur astronomer living in Eugene, Oregon, and a frequent contributor to Sky & Telescope. Pruett wrote on a variety of topics, especially fireball meteors. In his article on Blue Moons, he mentioned the 1937 Maine almanac and repeated some of Lafleur's earlier comments. Then he went on to say, "Seven times in 19 years there were — and still are — 13 full moons in a year. This gives 11 months with one full moon each and one with two. This second in a month, so I interpret it, was called Blue Moon."
  7. ^ Barbuzano, Javier (January 1, 2023). "Native American Full Moon Names". Sky & Telescope. Retrieved May 20, 2024. While this name is not Native American, it is included here for completeness.
  8. ^ "Why do we have special names for full moons?". Royal Museums Greenwich. Retrieved May 20, 2024.
  9. ^ The New Encyclopaedia Britannica, Volume 16. Chicago. 2005. p. 602. ISBN 978-1-59339-236-9.{{cite book}}: CS1 maint: location missing publisher (link)
  10. ^ Gibbs, Philip (May 1997). "Why is the sky blue?". math.ucr.edu. Retrieved November 4, 2015. ... may cause the moon to have a blue tinge since the red light has been scattered out.
  11. ^ Philip Hiscock (August 24, 2012). "Once in a Blue Moon". Sky & Telescope. Retrieved May 27, 2019.
  12. ^ Harper, David (2023). "Once in a Blue Moon". obliquity.com. Retrieved May 14, 2024.