The final day of September will bring a rare lunar event that hasn’t occurred since March of 2014, a Black Moon.
The term Black Moon has several definitions, but one of the most common definitions is the second new moon in a calendar month. This is similar to the well-known Blue Moon, which is the name given to the second full moon in a calendar month.
Since it is a new moon, it will not be a visible event as the side of the moon that is illuminated will be facing away from the Earth.
The last time that two new moons fell in the same month was March of 2014.
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While some areas of the world, such as the United States, experience a Black Moon in September, it will not be the case for the entire world.
“It’s the second new moon this month in all of the Americas, but not in Europe and points east from there,” said Bob Berman, an astronomer for Slooh.
This is because the new moon occurs at 8:11 p.m. EDT on Sept. 30, so for areas in the Eastern Hemisphere, the new moon will officially occur after the calendar flips to October.
However, these areas will not miss out on a Black Moon. Another new moon will occur at the end of the month, giving the Eastern Hemisphere a Black Moon right around Halloween.
While this type of Black Moon happens about once every two and a half years, there are several other lunar events that fall under the same name.
Another type of Black Moon is when there are no new moons in a month. These can only happen in February and occur once every five to 10 years, said Berman.
“The phrase could also mean the third new moon when there are four in a season, which is actually also one of the definitions of a Blue Moon when the same thing happens to a full moon,” Berman added.
The next time that two new moons will fall in the same month for the Western Hemisphere will be in July of 2019.