Something rare will be occurring this Friday.  It will be a full moon and you ask “what is so rare about that?” Well,we basically have a full moon each  month but this full moon will be the second full moon in this calendar month of August . And since it is the second full moon in August it is also called a “Blue Moon”.  It is Blue in name only. The idea of calling it a Blue Moon as the second full moon in a month stemmed from the March 1946 issue of Sky and Telescope Magazine, which contained an article called “Once in a Blue Moon” by James Hugh Pruett.  This rare occurrence happens infrequently and can only happen when  the first full moon of a month occurs in the first two days of the month followed by the second full moon in the last two days of the same month.  That was the case this month with the first full moon happening on August 1st and the second one to take place on August 31st.                                                                                                                                                                                                                                                                     There can be two blue moons in a single calendar year.  That last happened in 1999. There were two full moons in January and two full moons in March and no full moon in February. So both January and March had Blue Moons.                                                                                                                                                                                                                                                                                                                                                                                   In case you are wondering, the next year of double blue moons is coming up in 2018.