Blue Moon

A Blue Moon is the second full moon in a calendar month. Usually months have only one full moon, but occasionally a second one sneaks in. Full moons are separated by 29 days, while most months are 30 or 31 days long; so it is possible to fit two full moons in a single month. A blue moon occurs about once in 2.5 years on average.

A blue moon can occur in January and the following March if there is no full moon at all in February, as is the case in the years 1999, 2018, and 2037.

Note that because the full moon occurs at different times (and therefore potentially on different calendar days and in different calendar months) in different time zones, the occurrence of blue moons is time zone (and daylight saving time) dependent

 

Blue Moons 2001 to 2104
(Universal Time)
  1. 2001, Nov 1, Nov 30
  2. 2004, Jul 2, Jul 31
  3. 2007, Jun 1, Jun 30
  4. 2009, Dec 2, Dec 31
  5. 2012, Aug 2, Aug 31
  6. 2015, Jul 2, Jul 31
  7. 2018, Jan 2, Jan 31 (!)
  8. 2018, Mar 2, Mar 31 (!)
  9. 2020, Oct 1, Oct 31
  10. 2023, Aug 1, Aug 31
  11. 2026, May 1, May 31
  12. 2028, Dec 2, Dec 31
  13. 2031, Sep 1, Sep 30
  14. 2034, Jul 1, Jul 31
  15. 2037, Jan 2, Jan 31 (!)
  16. 2037, Mar 2, Mar 31 (!)
  17. 2039, Oct 2, Oct 31
  18. 2042, Aug 1, Aug 31
  19. 2045, May 1, May 30
  20. 2048, Jan 1, Jan 31
  21. 2050, Sep 1, Sep 30
  22. 2053, Jul 1, Jul 30
  23. 2056, Mar 2, Mar 31
  24. 2058, Oct 2, Oct 31
  25. 2061, Aug 1, Aug 30
  26. 2064, May 1, May 30
  27. 2066, Dec 1, Dec 31
  28. 2069, Sep 1, Sep 30
  29. 2072, May 2, May 31
  30. 2075, Apr 1, Apr 30
  31. 2077, Oct 2, Oct 31
  32. 2080, Jul 2, Jul 31
  33. 2083, May 2, May 31
  34. 2085, Dec 1, Dec 31
  35. 2088, Sep 1, Sep 30
  36. 2091, Jul 1, Jul 30
  37. 2094, Jan 1, Jan 31
  38. 2096, Oct 2, Oct 31
  39. 2099, Aug 1, Aug 30
  40. 2102, Jun 1, Jun 30
  41. 2104, Dec 2, Dec 31

     

The mean time intervall is 2.577 years (2 years 7 months).

 

Gregorian year = 365.2425 days

lunation: 29.53058867 days

12,368277 lunations per year

0.368277 extra lunations per year

1 / 0.36827 years = 2.7153 years per extra lunations (2 years 8.6 months).

 

Web Links

http://scienceworld.wolfram.com/astronomy/BlueMoon.html

on blue moons

What's a Blue Moon? (Sky & Telescope)

What Is a Blue Moon? (Farmers' Almanach)

Full Moon Names and Their Meanings (Farmers' Almanach)

Blue Moon (NASA Science News)

Blue Moon of Kentucky (Song text)

Blue Moon of Kentucky (Elvis Presley)

Last Modified: 2010, Apr 01