No, a black supermoon won’t rise in your sky tonight
July 31, 2019
By Amy Sayle
You may have heard that today’s (July 31, 2019) new moon is a “black supermoon” that will make for exceptional stargazing when it rises tonight. This claim misleads in several ways.
Let’s start by breaking down that “black supermoon” term:
- Black moon. You didn’t learn about black moons in your astronomy class because astronomers don’t use that term. But some people have started using it to refer to a new moon that’s the second one to occur within a calendar month.
- Two new moons—or two full moons—or for that matter, two moons of any phase—will occasionally occur in the same calendar month because the Moon takes only 29½ days to cycle through its phases, and most months are 30 or 31 days long. When the Moon is full twice in the same calendar month, you’ll sometimes hear “blue moon” used to refer to that second full moon.
- Supermoon. This term, which was coined by an astrologer (not an astronomer), misleads because it implies that when the Moon happens to be a bit closer to Earth than on average, the Moon will look “super” big. It won’t.
And when the Moon is new, like it is today (7/31/19 for North America, 8/1/19 in some other time zones), you won’t see it at all. At new moon, the Moon is in the part of its orbit around Earth where the Moon lies between the Sun and Earth. That gives you two reasons you won’t see a new moon rising tonight:
- The part of the Moon that’s being illuminated by the Sun is the Moon’s far side. The side facing Earth is dark. You won’t see it.
- A new moon lies in the same general direction of the sky as the Sun. That means a new moon is above the horizon only when the Sun is also up, that is, only in the daytime. Thus, the new moon is most definitely not “rising tonight” in your sky, as at least one prominent news outlet claims.
But what about the exceptional stargazing that’s being promised? If there’s no moon in the night sky, doesn’t that mean more stars to see?
It’s true that when the Moon is up at night—especially if it’s near, at, or just past full moon—its bright light washes out dimmer stars from view. But it’s hardly unusual for the Moon not to be up at night when you’re outside looking at the sky. Only when the Moon is full will it be above the horizon the entire night.
That said, if your skies are clear tonight, by all means, go out and look up. The universe awaits you.
Morehead offers clear skies all the time in our planetarium theater. Check out the show “Carolina Skies” if you want 45 minutes of (simulated) night sky viewing and flying through the universe.
To view the real sky, join us at our free skywatching sessions. If the weather permits, we will have two in August: on Monday, August 12, 2019, at the Durham Hotel, and on Friday, August 23, 2019, at Historic Stagville. Find out more about our planetarium shows and skywatching sessions here.