A rare “black moon” will be visible over the night sky this week. The trouble is that nobody’s clear what exactly that means.
Friday’s new moon is the second that has risen this month. That, according to the most used definition, makes it a black moon – though that’s not the only way of defining it.
Naming moons has become an increasingly popular activity. People have over the last year or so been excited about blood moons, blue moons and supermoons – all of which refer to something, but have more or less connection with what the moon is actually up to.
The black moon is one of those new additions. And like the blue moon and others, it doesn’t actually refer to the colour of the moon or its appearance, but rather to where it fits in the yearly schedule.
So despite the common definition of a black moon being the second new moon of the month, other definitions are common. Each of them is based on what the moon does in the year and where the new moon – when the lit-up side of the moon is facing away from the Earth and so is invisible – appears.
Some definitions, for instance, say that the black moon is when February skips a full moon – which happens every 19 years. That perhaps makes the most sense, since it means that the month doesn’t actually have a visible new moon at all.
Others say that it refers to any month that skips a new moon. That also makes some sense for the same reason.
But the most common meaning of a black moon still rules out. That means that this week’s new moon will be black, or at least called it, by everyone in the western hemisphere.
As such, it is the opposite of a blue moon – when the full moon appears twice in one calendar month.
