Discover Your Two 15-Minute Windows To Watch This Weekend’s Moonrise (And Why It Will Glow Orange, Not Blue)
Are you ready for 2021’s only “Blue Moon?” Since more of us are outside enjoying a vacation at this time of year in the northern hemisphere, August’s full Moon—the “Sturgeon Moon”—is one of the most popular of the year.
So why is it also called a “Blue Moon” this year? Find out why—and why the “Blue Moon” will actually look orange—in our guide to precisely when and where to stand and stare at the dramatic rise of August’s “Blue Sturgeon Moon.”
When is the full ‘Blue Sturgeon Moon?’
The Moon will be full at 12:02 Universal Time on Sunday, August 22, 2021.
Although a lot of people presume that is the best time to see the full Moon, the “Blue Sturgeon Moon” will be at its most dramatic at moonrise.
This month there are two successive nights when you should look for the full Moon.
Best times to see the ‘Blue Sturgeon Moon’
The “Blue Sturgeon Moon” will be best seen at moonrise where you are. You can consult a moon calculator to get the precise times of moonrise for your exact location, but as a rough guide here are some times for three major cities:
Best times to see the ‘Blue Sturgeon Moon’ on Saturday, August 21, 2021
- London: sunset is at 8:12 p.m. and moonrise is at 8:22 p.m.
- New York: sunset is at 7:46 p.m. and moonrise is at 7:49 p.m.
- Los Angeles: sunset is at 7:34 p.m. and moonrise is at 7:36 p.m.
Best times to see the ‘Blue Sturgeon Moon’ on Sunday, August 22, 2021
- London: sunset is at 8:10 p.m. and moonrise is at 8:45 p.m.
- New York: sunset is at 7:45 p.m. and moonrise is at 8:21 p.m.
- Los Angeles: sunset is at 7:32 p.m. and moonrise is at 8:11 p.m.
Will the ‘Blue Sturgeon Moon’ look blue?
No! The full Moon will look like it always does, though for about 15 minutes as it rises in the east it will look orange, turning to a pale yellow as it rises higher into the sky, before appearing a bright, whitish-grey.
The reason is something called Rayleigh scattering. Earth’s atmosphere contains oxygen and nitrogen molecules that absorb some wavelengths of light more effectively than others.
Colors in the sun’s light with short wavelengths, such as blue, strike more particles and are therefore more often absorbed . They scatter more easily, which is why the sky is blue during the day. Colors with longer wavelengths, such orange, more easily pass through the atmosphere uninhibited.
When you look at moonrise you’re looking across the planet so you’re looking through a lot of atmosphere. Rayleigh scattering is intensified, with orange dominating the light that makes it to your eyes.
Why is it called the full ‘Blue Sturgeon Moon?’
Astronomers define a “Blue Moon” as the third full moon during a season that has four full moons. There is another definition—when two full Moons occur during the same calendar month—but that’s not what’s happening here.
Why are there four full Moons this summer?
It’s a quirk of the calendar, that’s all. The Moon takes 29 days to orbit the Earth while the seasons last for three months, so every so often four full Moon squeeze into one astronomical season.
This year the “Super Strawberry Moon” occurred on June 24, 2021—just a couple days after the solstice that marked the beginning of summer—while the next full Moon, the “Corn Moon,” will rise on September 20, 2021—just a couple of days before the autumnal equinox that begins fall.
Why there are two successive nights when you should look for the rise of the ‘Blue Sturgeon Moon’
Only when the Moon is full does it rise during dusk. It’s impactful precisely because you can see it appear just after the Sun has set, when there’s still a lot of light left; at all other times the Moon rises either in a bright sky or a completely dark sky.
Since the Moon more or less travels along the same path in the sky as the Sun—the ecliptic—a full Moon (which is opposite the Sun) is low when the Sun is high, and vice versa.
In effect it mimics the Sun’s behaviour precisely six months ago. Back in February the Sun was only in the northern hemisphere’s sky for a few hours, rising in the southeast and setting in the southwest. The time of sunrise and sunset didn’t change much from one day to the next. Ditto the full moonrise this month—which is why for two successive nights it will occur just after the sunset.
So enjoy the rising “Blue Sturgeon Moon,” not because it’s blue, but because there are two!
Wishing you clear skies and wide eyes.