OFFSET
1,1
COMMENTS
A blue moon is the second full moon to occur in a single calendar month. The sequence contains the (Gregorian) years during which each succeeding blue moon will occur.
This is a new version of the definition. The original definition is that of the third full moon in a season which has four. All of the definitions depend on the longitude of the observer. Unless specified otherwise, we should assume that we refer to UTC. A special subsequence is that of the years (1999, 2018, 2037, ...) in which there is no full moon in February, which usually implies that there are two in January as well as in March. This happens most often at an interval of 19 years, but sometimes also 8 or 11 years, for example in 1589, 1608, 1627, 1646, 1665, 1676, 1684, 1695, 1714, 1741, 1752, 1760, 1771, 1790, 1798, 1809, 1828, 1847, 1866... - M. F. Hasler, Dec 08 2017
REFERENCES
Philip Hiscock, Folklore of the Blue Moon, MUN Folklore & Language Archive, Memorial University of Newfoundland, St John's, Newfoundland A1B 3X8, Canada.
Donald W. Olson, What's a Blue Moon?, Sky & Telescope (Archives), May 1999, 36.
LINKS
David Harper, Blue moon calculator.
Phillip Hiscock, Folklore of the Blue Moon, International Planetarium Society, 1993.
Donald W. Olson, Richard T. Fienberg and Roger W. Sinnott, What's a Blue Moon?, Sky & Telescope, (Archives), Jul 2004, 134.
Wikipedia, Blue Moon.
EXAMPLE
a(7) = 2018 because at least one blue moon will occur that year.
a(8) = 2018 because after the first blue moon in January, a second blue moon occurs in March of that year.
CROSSREFS
KEYWORD
nonn
AUTHOR
H. Lee Price, Jan 30 2007
EXTENSIONS
Edited by M. F. Hasler, Dec 08 2017
STATUS
approved