Next Blue Moon coming up August 20-21, 2013

Blue Moon can be second of two full moons of a calendar month. Or Blue Moon can be third of four full moons in a season. Upcoming Blue Moon is the seasonal kind.

Yes, it will be a Blue Moon that lights up the night sky on August 20-21 from dusk till down! But it won't be as Blue Moon by the most popular term - the second of two full moons to occur in the same calendar month. Nor is the moon likely to be blue in color, as that's caused by exceedingly rare atmospheric conditions.

Rather, the August 2013 full moon will present the third of four full moons to fall in the same season. A season is defined as the period of time in between a solstice and an equinox - or vice versa. This full moon is the third of four full moons to take place in between the June 2013 solstice and the September 2013 equinox. That makes the August 2013 full moon a Blue Moon!

The moon turns full on August 21, at 1:45 Universal Time.  Although the full moon happens at the same  moment worldwide, the clock reads differently by time zone. The moon turns full in the United States on Tuesday, August 20, at 9:45 p.m. EDT, 8:45 p.m. CDT, 7:45 p.m. MDT or 6:45 p.m. PDT. Astronomically speaking, the moon is full when it's most directly opposite the sun for the month.