A black moon is a rare moment in the celestial calendar… and there’s one coming soon to our skies.
What is a black moon?
Most commonly, a black moon is a new moon with an unusual name and unusual timing. There's no universally accepted definition for it, but some refer to it as the second new moon that appears in a single month, similar to a blue moon, which is the second full moon in a calendar month.
In astronomical terms, a new moon is the first part of the lunar cycle - the Moon's transition from full moon to full moon that we all witness in the night sky. It's the period when the Moon sits between the Earth and the Sun, which makes it practically invisible. Astronomers favour this period for stargazing, as it leads to darker skies.
A black moon happens every 29 months or so, which means a black moon rises about once every two to three years. This rhythm is a result of the lunar cycle being shorter a calendar month, lasting just 29.5 days.
The second main definition of black moon is an extra full moon in a single season. Because the Earth’s seasons are approximately three months long, we usually have three new moons in a season – but if it has four, the third new moon of the four is called a black moon.
Does the whole world experience a black moon?
Depending on which time zone you’re in, you may or may not experience a black moon. This is because 30 September for some parts of the world, for instance, will already be 1 October for other parts, meaning some countries are experiencing their second new moon of the month, while others are already into the next month. The timing of these events are based on Universal Time, which is essentially Greenwich Mean Time – i.e. British time in winter, before the clocks go forward for British Summer Time.
The same applies for the seasonal definition of a black moon – if the date of the new moon is on the cusp of a season end, some time zones will have already slipped into the next.
When is the next black moon?
The next black moon will take place on 23 August 2025. But this is the seasonal definition of a black moon – the third of four new moons in a single season. In this instance, it’ll be the third new moon of summer, which runs from 21 June to 22 September in the astronomical season calendar. The additional fourth new moon of the summer season will scrape through on 21 September.
The next black moon after this one will occur on 31 August 2027, which will be in line with the definition of a black moon as the second new moon in a calendar month.
There will also be four full moons this summer: 11 June (Strawberry Moon), 10 July (Buck Moon), 9 August (Sturgeon Moon) and 7 September (Harvest Moon).
Can you see the black moon?
The Black Moon itself can’t actually be observed, because it’s a new moon, so is invisible to the naked eye.
More moon stories
- When are this year's supermoons and why do they happen? These are the dates to add to your diary – and how you can capture their magic with photography
- Perseid meteor shower set to fill our skies this week – here’s how to see hundreds of fireballs shooting across the sky
- How the Moon affects wildlife
Top image credit: Getty Images
