The phrase “black moon” may sound dramatic, but if you look to the skies this Friday, you won’t see anything special. In fact, you won’t see any moon at all, because it will have disappeared from the night sky for the second time in a month.
Internet searches for information on the upcoming black moon may be taking over trending lists, but it’s a far more mundane occurrence than its name might suggest: A black moon is just another new moon.
For the most part, the moon’s waxing and waning cycles line up with the standard 12 month calendar in such a way that there is one full moon and one new moon each month. However, because the dates aren’t exactly synced up with the moon’s shifts, that means that every so often (once in a black moon, some might say), an extra full moon or new moon will appear in a single month, Bec Crew reports for ScienceAlert.
For most of the month, the moon lights up the night sky because it is reflecting some of the sun’s light. When it waxes, it gradually passes further away from the sun, reflecting more and more light. As it wanes, the moon passes in between the Earth and the sun so its dark side faces us, Eric Grundhauser writes for Atlas Obscura.
On new moon nights, the orb becomes nearly invisible to the naked eye, which makes this nighttime event not particularly exciting to watch. On the plus side, however, without the vibrant moon, stargazing will be exceptionally good this weekend.
Scientifically speaking, the black moon is more of a scheduling fluke than an exciting occurrence. Even so, it is fairly uncommon for them to occur. Black moons happen about once every 32 months and the last time one showed up was in March 2014.
According to Space.com's Joe Rao, this black moon will only occurr in the western hemisphere. In the eastern hemisphere, it will occur on October 1, kicking off the month with a new moon.
"Black moon" is far from the only fancy term describing an ordinary occurrence of the moon’s orbit. In recent years, the term “supermoon” has become popularized, though it really just marks times when the moon is as its closest point to the Earth and looks a little bit bigger and brighter than usual. The same goes for “blood moons,” which are a kind of lunar eclipse, Rao reports.
The best example for a similar kind of lunar phase “branding” might be the “blue moon,” which is supposedly the black moon’s opposite. Like the black moon, the term describes a second new moon in a month, a blue moon is when a second full moon appears in the sky. But the association only goes back to the 1940s, Rao reports. The meaning comes from a misinterpretation of an arcane rule found in the now-defunct Maine Farmer’s Almanac by James Hugh Pruett in a 1946 article for Sky & Telescope. However, the term got picked up in the 1980s by a radio show and quickly became popularized.
It’s unclear whether or not “black moon” will become as widely-known as blue moon, especially given that there isn’t much for viewers to take in. In any case, if you clouds move in Friday, don’t worry—you wouldn’t have seen the moon anyway.