The skies of the Western Hemisphere are set for a “black Moon” on Friday night. Fortunately, you can put away the tin foil hats and stop repenting your sins. Despite some of the headlines, it doesn’t mean the second coming of a messiah or an ensuing apocalypse.
It does, however, mean a rare astronomical event that only happens roughly every 32 months.
A black Moon is the name given to the second new Moon in a calendar month. A new Moon is the first phase of the 29.53-day lunar cycle as the Moon orbits Earth. At this phase of the cycle, the Moon is invisible to the naked eye as its illuminated side faces away from Earth and towards the Sun, meaning it’s shrouded in darkness (and thus hard to see).
The black Moon will officially take place on Friday 30 September at 8.11pm EST (5.11pm PST) in the Western Hemisphere. For those in the Eastern Hemisphere (Europe, Africa, Asia, and Australasia) on the other side of the globe, the black Moon will arrive just in time for Halloween on October 30, or October 31 for the eastern-most regions.
As a side note, a blue Moon is when a full Moon occurs twice in a calendar month, according to the newer “non-traditional” definition. It doesn’t literally mean the Moon is blue. As NASA explains, “Squeezing a second full Moon into a calendar month doesn't change its color.”
Simply, a black Moon just means the Moon appears almost invisible in the sky for the second time in a calendar month. It’s perhaps not the most dramatic of astronomical oddities, but at least it means there's no apocalypse and you can keep your weekend plans.