Do You See A Moon Halo Or A Moonbow?

It’s late at night, light wispy clouds float gently by as the nearly full Moon shines down. But then you notice a faint, ghostly glow in the sky. It looks like a ring around the Moon, a delicate circle of off-white light with the Moon sitting perfectly in its center. This rare event is called a Moon halo. It happens when moonlight bends through lots of six-sided ice crystals in the Earth’s atmosphere to create a huge, perfect circle of light.

Moon halos may occur all year round but are slightly more noticeable during colder months in the Northern Hemisphere when more ice crystals can form at high altitudes. Legends say that a Moon halo is a warning that bad weather is coming soon.  Although it may not be true every time, meteorologists have documented that high cirrus clouds that help form Moon halos often come before storm systems.

The radius of a Moon halo is always the same—about 22 degrees from the Moon. You can use your hand at arm’s length to measure that angle in the sky. (See our illustration here.) Spread out your fingers, cover the Moon with your thumb, and your pinkie should reach the edge of the ring around the Moon.

A ring around the Moon (Moon halo).

How About A Moonbow (Night Rainbow)?

Experiencing a rainbow shining majestically before a bank of dark clouds is one of the most amazing sights on Earth. Sunlight is passing through water vapor in the atmosphere which shines in a colorful arc. But can the Moon be bright enough to cast a similar shape during the nighttime—a moonbow? It can, but only in very select places and under perfect conditions.

First you need water vapor, lots of it, off which the moonlight can reflect. This could be kicked up by large waterfalls or forest mist that spread over a large area.

Then you need an almost full Moon. Only the light of the Moon near its brightest phase casts enough light on the water vapor to create a suitable moonbow (night rainbow) your eye can detect.

Also you need a location with no trees between the mist and the Moon. And just like a rainbow that appears on the opposite side of the sky from the Sun, the mist must be on the opposite side of the sky from the Moon.

Other things that help is a location far from city lights where the sky is naturally darker. A moonbow can also only form if there are no clouds and the Moon is low in the sky. This means the best viewing times are usually 1-2 hours after sunset, which is when a full Moon rises.

There are only three places in the United States where moonbows are regularly seen: Niagara Falls, New York, Yosemite Falls, California, and Cumberland Falls, Kentucky. Moonbows have been spotted through mists and light rain in forests of Hawaii and Costa Rica, but they are harder to predict.

Even under perfect conditions from the perfect location, a moonbow is still incredibly faint. Long exposure photography can bring out all the usual colors from red to violet. To your naked eye, however, the arc of light from a moonbow appears mostly white with very little color evident.

Check out the dates of the next full moons and take a pilgrimage to a waterfall on a clear evening. See if you can catch a nighttime rainbow in the mist.

Join The Discussion

Have you ever seen a ring around the Moon or a moonbow (night rainbow)?

Share your experience (and photos!) with your community here.

What questions do you have? Let us know in the comments below!

A Halo Around The Sun (Sundog)

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Dean Regas is an expert astronomer and published author..
Dean Regas

Dean Regas is an expert astronomer and a renowned author who has written six books, including 100 Things to See in the Night Sky and How to Teach Grown-Ups About Pluto. An astronomer with more than two decades of experience, Dean is a dynamic writer and public speaker who brings the complicated field of astronomy down to Earth for students of all ages. From 2010-2019, he was the co-host of the PBS program Star Gazers. He is a frequent guest on National Public Radio’s Science Friday with Ira Flatow and NPR's Here & Now. He also hosts a popular astronomy podcast called Looking Up with Dean Regas. Learn more about him at www.astrodean.com

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Anna

Last night 12/26/23 in San Diego CA

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Anne Becker

I saw a halo around the moon quite recently. All the colors of the rainbow were there. It was not the first time. But my husband said he did not see it. How could I see it and he not see it??

Rebecca Hopkins

I saw a moonbow long before either the internet nor camera phones existed. I was a teen, in Felton, Delaware. And while riding in the front seat of a car, I looked through the windshield and directly ahead in the sky was a silver, shimmering cord of reflected light with barley any color visible but silvery shimmering white. It was INCREDIBLE. Majestic. Awe inspiring. Magic. Never saw one before or since, but I’ve never forgotten it. It’s an experience everyone should have at least once. Once had, you’ll never forget it.

Heather

That does indeed sound incredible. Thank you for sharing it with us as well, and sometimes those memories that aren’t physically documented are the most treasured ones.

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Mia. Fowler

Was taking a picture of the water I took one didn’t like it to much so I took another one.I liked it so game over so I thought…little did I know I was standing at the end of a moon bow.3days latter I went back to look at the pictures looking at the first one several minutes could not figure out what was in the picture so I ran google lens over it and moon bow came up. About 10 photos. So I posted it saying I had no idea I was standing at the end of a rainbow when I took this picture to Facebook.Then courious on how google knew it was a moon bow rainbow I went back to the picture enlarged it an sure enough I seen color so I can say. I got a pc

Beverley

I saw a moonbow on Unst, Shetland a few days ago. It was magic.

Staryl Dawn Gilley

I spotted a Moon halo last night in OREGON. I did get photos. It didn’t last very long only about 3 minutes.

Sandi Duncan

We saw one too last night — let us know if you get any precipitation!

Dan meadows

There are only two places in the world where you can see a moonbow on a predictable basis. One of them is Cumberland falls state park in Kentucky. Once a month, when the moon is full, and the sky is perfectly clear. The water must have good flow( plenty of mist).
If the water level is low, you probably will not see it.Arrive early, sometimes there is a crowd. Bring a lawn chair, maybe a blanket in cold weather, arrive before dusk. You may have to wait for a little while, it doesn’t appear until the moon is pretty far up in the sky. There is lodging nearby ,and a restaurant ,and a gift shop. If you have time, there is a second water in the park (eagle falls), which is very beautiful.

Susan Higgins

Sounds beautiful, Dan! If you ever get a photo, we’d love to see it! Send it to [email protected]!

Pam Caccia

we viewed a moonbow on the Big Island of Hawaii. We were passing over the mountain from Kona to Kamuela at night.
There was light rain on one side and clear moonlight on the other side. Suddenly we saw a spectacular moonbow
with clear varying shades of silver- at least 8 rings and complete arcs.

Marcia Tullous

My family and I just saw our first Moonbow last night! It was amazing! I had never even heard of a moonbow before!

monique

I’ve seen moonbow just yesterday evening for the first time, in Croatia..didn’t knew it existed! It was just a spot but it was lovely.

urvi

ohhh this is so going to help me for my project!

Susan Higgins

Oh, good! We’re glad we can help, Urvi!

Queen Bee Tink

I saw a MoonBow last night. My husband and 3 boys did not.. so they thought I was crazy. It was clear to me. At one point I saw red, orange,yellow, green, blue and violet. Mostly though the red and violet I did not see. According to Chick Trainor’s comment ..there was less than a finger measurement width from moon to colored ring ( I didn’t know that would mean something .. but was trying to get my husband to see it!) well .. we just had a very bad storm with CLoud to Ground lighting!

Wondering if only certain people with eye conditions can see these Moonbows ? It was even much brighter without my glasses on but no one else saw it

Chick Trainor

Thanks for the information,Tiffany Means. Here is something related, for you. The other day a local native Eskimo here in Nome,Alaska told me about a weather rule another man told him. That man was also an Eskimo and he was for many years a weather service observer on the radio here. It relates to the ring around the moon. When at night you observe the Moon with a ring around it, extend your flat hand up and out,with fingers together in front of your face,fill the space from the edge of the Moon out to the inside of the ring. If you can only fit three fingers between those two locations then you only count three in your calculation…if 4 fingers,then you calculate using 4. Each finger will represent 4 days….so…if it’s 3 fingers you’ve used,it is 3×4(days)…or 12 days total. If it is 4 fingers then it will be 4 times 4 days or 16 days total. Whatever it comes out to be…for these examples either 12 days or 16 days, that is the time you have left before the next storm.

Lee Michael

Interesting fact – never knew that.

Chick Trainor

Indigenous people are tied to their surroundings. That historically has been a life or death decision especially in the winter.

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