Once in a Blue Moon

Two New Moons in one month

If the second Full Moon in one month has a special name, what about the second New Moon?

Most people don't notice New Moons. It's easy to see the Moon when it's full, but the only way to tell when a New Moon is happening is during an eclipse, or by referring to an almanac or using Obliquity's Moon Phase calculator.

To Wiccans, the second New Moon is called the Black Moon, and any magic worked during that period is deemed to be especially powerful.

Of course, the chances of two New Moons falling within one calendar month are just the same as two Full Moons, but because New Moons are generally invisible, most people tend not to notice the occasions when a month has two of them.

That's not to say that New Moons aren't important to non-astronomers. To the world's Muslims, the date of New Moon is of great interest, since the Islamic calendar is governed by the phases of the Moon: the start of each month is marked by the first sighting of the new crescent Moon.

Another definition - four New Moons in a season

According to an article in the May 1999 issue of Sky and Telescope, the traditional definition of a Blue Moon is the third Full Moon in a season which has four Full Moons. Compilers of almanacs such as the Maine Farmer's Almanac would use a coloured symbol to denote this third Full Moon, hence the name.

Similarly, a Black Moon can be the third New Moon in a season which has four New Moons.

Here is a list, by that definition, of the Black Moons between 1900 and 2999. Dates and times are given in Greenwich Mean Time.

YearDayTime (GMT) YearDayTime (GMT)
1900Dec 2200:012001Sep 1710:27
1903Sep 2104:312004Jun 1720:27
1906Jun 2123:052006Sep 2211:45
1909Jun 1723:282009Sep 1818:44
1911Sep 2214:372012Jun 1915:02
1914Sep 1921:332015Mar 2009:36
1917Jun 1913:022017Sep 2005:30
1919Dec 2210:552020Sep 1711:00
1922Sep 2104:382023Jun 1804:37
1925Jun 2106:172025Sep 2119:54
1928Jun 1720:422028Sep 1818:23
1930Sep 2211:412031Jun 1922:24
1933Sep 1918:212034Mar 2010:14
1936Jun 1905:142036Sep 2001:51
1938Dec 2118:072039Sep 1808:22
1941Sep 2104:382042Jun 1719:47
1944Jun 2017:002044Sep 2111:03
1947Jun 1821:262047Sep 1918:31
1949Sep 2212:212050Jun 1908:21
1952Sep 1907:222052Dec 2104:14
2053Jun 1610:51
1955Jun 2004:122055Sep 2102:19
2058Jun 2100:34
1960Sep 2023:122061Jun 1718:02
1963Jun 2111:462063Sep 2209:21
1966Jun 1820:092066Sep 1913:47
1968Sep 2211:082069Jun 1902:13
1971Sep 1914:422071Dec 2111:46
2072Jun 1609:57
1974Jun 2004:562074Sep 2101:28
1976Dec 2102:082077Jun 2012:54
1979Sep 2109:472080Jun 1718:40
1982Jun 2111:522082Sep 2210:03
1985Jun 1811:582085Sep 1901:06
1987Sep 2303:082088Jun 1901:53
1990Sep 1900:462090Dec 2101:29
1993Jun 2001:522093Sep 2018:16
1995Dec 2202:222096Sep 1615:10
1998Sep 2017:012099Jun 1816:10