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Blue Moon


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Blue Moon

  1. 1. BLUE MOONMarch 17, 2013 Tofique Fatehi BLUE MOONThe time period between one full moon and the next (lunation) is approximately 29.53 days. AGregorian year has approximately 365.25 days. So, in a year there will be 365.25/ 29.53 =12.369 lunations. Therefore, there will be at least 12 full moons in a year, usually, one full moonper month.The month of February has 28 or 29 days, which is a fraction less than a lunation. So, a situationcan arise that the full month of February fits entirely within a lunation, and that there is no fullmoon in February. To compensate for this, any one of the other months in the year may havetwo full moons.The first of these full moons will occur in the beginning of that month, on the 1st or 2nd of themonth and the second one will occur a lunation later, that is in 29.53 days, but before the monthgets over, that is on the 30th or 31st of the month.A second full moon in the same month is called a “blue moon”.With 12.369 lunations in a year, at the end of each year, a fraction of a lunation, 0.369, is leftover, which will be carried forward and added to the next year. When all these fractions add upto one or more, there will be 13 full moons in that year!This would imply that there is at least one month in that year which has two full moons in it, andthat all other months have one full moon each. In other words, this will be a blue moon year.This is a fairly rare phenomenon, occurring, on the average, once in two or three years. This iswhy any rare occurrence is spoken of as “once in a blue moon”. It has nothing to do with thecolor of the moon.An even rarer phenomenon can occur with two blue moons in a single year! At first sight, thismay seem to imply that there will be 14 full moons in such a year. However, this is not so. Sincethe number of a lunations in a year is 12.369 which is a fraction more than 12 and a fraction lessthan 13, there can only be either 12 or 13 full moons in a year. Hence, if there are to be 2 bluemoons in a year, there has to be one month in that year without a full moon. Again, onlyFebruary can be that month.Blue Moon© 2013 Tofique Fatehi Page 1
  2. 2. SUMMARY  There can be either 12 or 13 full moons in a year.  If there are two full moons in the same month, the second full moon is termed as a “blue moon”.  If there are 12 full moons in a year, then either o each of the 12 months has one full moon, or o February has no full moon and one of the other 11 months has a blue moon. All other months have a full moon each.  If there are 13 full moons in a year, then either o Any one month (except February) in the year has a blue moon, and the other 11 months (including February) have one full moon each, or o February has no full moon and two of the other 11 months have a blue moon. (It may be mentioned that the first blue moon is always in January, and the second blue moon is in March or April.)See the table of blue moons below.Blue Moon© 2013 Tofique Fatehi Page 2
  3. 3. TABLE OF BLUE MOONS Here is a table listing all the blue moons in this century, from 2001 to 2099. There are only 3 years with two blue moons in them. They are marked in blue. Date Time Date Time Friday, November 30, 2001 20:51:10 Wednesday, July 30, 2053 17:08:32 Saturday, July 31, 2004 18:06:05 Friday, March 31, 2056 10:26:26 Saturday, June 30, 2007 13:50:25 Thursday, October 31, 2058 12:54:58 Thursday, December 31, 2009 19:14:20 Tuesday, August 30, 2061 22:20:53 Friday, August 31, 2012 13:57:45 Friday, May 30, 2064 10:37:03 Friday, July 31, 2015 10:45:46 Friday, December 31, 2066 14:42:26Wednesday, January 31, 2018 13:27:46 Wednesday, March 30, 2067 20:11:05 Saturday, March 31, 2018 12:37:46 Monday, September 30, 2069 18:12:11 Saturday, October 31, 2020 14:51:29 Tuesday, May 31, 2072 22:19:43 Thursday, August 31, 2023 1:37:05 Tuesday, April 30, 2075 18:40:43 Sunday, May 31, 2026 8:46:46 Sunday, October 31, 2077 10:39:00 Sunday, December 31, 2028 16:49:45 Wednesday, July 31, 2080 19:16:42 Tuesday, September 30, 2031 18:58:02 Monday, May 31, 2083 9:43:39 Monday, July 31, 2034 5:56:35 Monday, December 31, 2085 0:00:58 Saturday, January 31, 2037 14:05:42 Thursday, September 30, 2088 15:28:47 Tuesday, March 31, 2037 9:54:43 Monday, July 30, 2091 12:03:20 Monday, October 31, 2039 22:36:54 Sunday, January 31, 2094 12:40:11 Sunday, August 31, 2042 2:05:14 Friday, April 30, 2094 13:58:47 Tuesday, May 30, 2045 17:53:13 Wednesday, October 31, 2096 11:20:22 Friday, January 31, 2048 0:16:32 Sunday, August 30, 2099 17:59:15 Friday, September 30, 2050 17:32:47 Except as otherwise expressly permitted under copyright law, no copying, redistribution, retransmission, publication or commercial exploitation of this material will be permitted without the express permission of the copyright owner. In the event of any permitted copying, redistribution or publication of copyright material, no changes in or deletion of author attribution, trademark legend or copyright notice shall be made. You acknowledge that you do not acquire any ownership rights by downloading this copyrighted material. Blue Moon © 2013 Tofique Fatehi Page 3