Top 5 Most Recent Articles
  1. Mars's Ancient Water Works
  2. Artificial Intelligence Aids Astronomers
  3. Make Way for Makemake
  4. August 1st's Eastern Solar Eclipse
  5. This Week's Sky at a Glance
Top 5 Most Popular Articles
  1. August 1st's Eastern Solar Eclipse
  2. Mars's Ancient Water Works
  3. This Week's Sky at a Glance
  4. Have You Seen Comet Boattini?
  5. Jupiter's Third Red Spot May Have Survived
Top 5 Most Emailed Articles
  1. This Week's Sky at a Glance
  2. Make Way for Makemake
  3. Jupiter's Third Red Spot May Have Survived
  4. August 1st's Eastern Solar Eclipse
  5. Tunguska: 100 Years and Counting


home > observing > celestial objects > moon
email this > print this > save this > rss >

What's a Blue Moon?

The trendy definition of "blue Moon" as the second full Moon in a month is a mistake.

by Roger W. Sinnott, Donald W. Olson, and Richard Tresch Fienberg

Rising full Moon
A rising full Moon lights the scene in The Fishing Party, painted by Fitz Hugh Lane after a visit to the coast of Maine in August 1850. That month contained a Fruit Moon, according to the Maine almanac's rules.
Recent decades have seen widespread popular embrace of the idea that when a calendar month contains two full Moons, the second one is called a "Blue Moon." The unusual pattern of lunar phases in early 1999 — two full Moons each in January and March, and none at all in February — triggered a groundswell of public interest. Countless newspapers and radio and TV stations ran stories about Blue Moons.

In an article "Once in a Blue Moon", folklorist Philip Hiscock traced the calendrical meaning of the term "Blue Moon" to the Maine Farmers' Almanac for 1937. But a page from that almanac belies the second-full-Moon-in-a-month interpretation.

With help from Margaret Vaverek (Southwest Texas State University) and several other librarians, we have now obtained more than 40 editions of the Maine Farmers' Almanac from the period 1819 to 1962. These refer to more than a dozen Blue Moons, and not one of them is the second full Moon in a month. What's going on here?

1 2 3 Next Page >


Sky Publishing, a New Track Media Company
Copyright © 2008 New Track Media. All rights reserved.
Sky & Telescope, Night Sky, and SkyandTelescope.com are registered trademarks of New Track Media