John -
 
The modern definition of a 'Blue Moon' is the second full moon in a calendar month. The next 'Blue Moon' will occur on 6/30/2007 which is the 99th anniversary of the Tunguska Blast. It will be 234 days from 11/8/2006 to 6/30/2007. This information came from this site: http://www.infoplease.com/spot/bluemoon1.html . I suggest reading that site for the additional information and reading their link: http://www.infoplease.com/ce6/society/A0857114.html on the 'The Christian Ecclesiastical Calendar'.
 
- Bob