What makes a halo around the sun or moon?

A bright ring or halo around the cloud-covered sun.
View at EarthSky Community Photos. | Anubha Singh in Hyderabad, India caught this beautiful 22-degree halo around the sun on June 2, 2021. Thank you, Anubha!

What causes halos?

We get many messages throughout each year from people who’ve just spotted a large ring or circle of light around the sun or moon. Scientists call them 22-degree halos. They bear this name because the radius of the circle around the sun or moon is approximately 22 degrees.

There’s an old weather saying: ring around the moon means rain soon. There’s truth to this saying, because high cirrus clouds often come before a storm. Notice in these photos that the sky looks fairly clear. After all, you can see the sun or moon. And yet halos are a sign of high, thin cirrus clouds drifting 20,000 feet (6 km) or more above our heads.

These clouds contain millions of tiny ice crystals. The halos you see are caused by both refraction, or splitting of light, and also by reflection, or glints of light from these ice crystals. The crystals must be oriented and positioned just so with respect to your eye, for the halo to appear.

That’s why, like rainbows, halos around the sun – or moon – are personal. Everyone sees their own particular halo, made by their own particular ice crystals. So they are different from the ice crystals making the halo of the person standing next to you.

A word of caution when taking solar halos

Take care when photographing solar halos. Pointing a camera directly at the unobscured sun can damage it. Never look directly at the sun, even when it is visible through clouds.

A halo around the sun, with birds flying in the foreground.
View at EarthSky Community Photos. | Jayesh Jayesh J of Vadodara, Gujarat, India caught this beautiful 22-degree halo around the sun on August 29, 2020. Thank you, Jayesh!

Are halos more common at high latitudes?

We asked Les Cowley of the website Atmospheric Optics if halos around the sun and moon are more frequently seen at high latitudes and less commonly seen closer to the equator. He said:

That’s a good question that is not easy to answer accurately because no halo frequency statistics are collected except in one or two mid-latitude European countries.

We need to distinguish between (a) halos formed by low level diamond dust during very cold weather and (b) halos formed by ice crystals in high cirrus cloud.

Obviously (a) halos only occur in polar regions or countries with very cold winters (Canada for example is not high latitude).

(b) Halos can occur anywhere on the planet during winter or summer. Their frequency depends on the frequency of cirrus coverage and whether it has had a history such that it contains halo forming crystals. The latter is hard to predict. For example, there are major differences in halo frequencies and types of halos across even 200 miles [300 km] in the U.K.

If you see a halo, notice this!

Because moonlight isn’t very bright, lunar halos are mostly colorless. However, you might notice red on the inside and blue on the outside of the halo. These colors are more noticeable in halos around the sun. If you do see a halo around the moon or sun, notice that the inner edge is sharp, while the outer edge is more diffuse. Also, notice that the sky surrounding the halo is darker than the rest of the sky.

Some halo photos

Cloudy and hazy sky with halo around the sun.
View at EarthSky Community Photos. | Supriya Chakrabarty of Kolkata, West Bengal, India, captured this halo around the sun on March 21, 2023, and wrote: “22 Degree Solar Halo from Kolkata India.” Thank you, Supriya.
Halo around the moon, Mars, Pleiades and a few stars.
View at EarthSky Community Photo. | Sheryl R. Garrison captured this image on January 3, 2023 in Southern Alberta, Canada, and wrote: “I love reading EarthSky’s newsletter in the morning. It reminds me of what to look for in the night sky. When I went outside after dark, not only did I see Mars near the Moon but there was an added bonus of a lunar 22-degree halo.” Thank you, Sheryl!
Fisheye view of sky with moon and planets labeled.
View at EarthSky Community Photos. | Mei-Ying Lee in Taipei, Taiwan, took this image of the planets on June 21, 2022. Meiying wrote: “Today is the summer solstice and the sunrise is very early. In the early morning, despite the interference of thin clouds, the planets were still arranged in order from east to south in the sky. The 5 planets are arranged on the ecliptic plane and draw a big arc. Today’s thin clouds just allow the formation of the lunar halo, adding to the mystery and beauty of the planetary arrangement.” Thank you, Meiying!

And more halo photos

Multiple rings of light around the moon.
View at EarthSky Community Photos. | Soumyadeep Mukherjee in Kolkata, West Bengal, India, captured this photo of a lunar halo on September 25, 2021. Soumyadeep wrote: “What a busy sky it was at midnight. Multiple lunar halos crowning the moon; Pleiades coming near the moon; the “hunter” Orion rising; many constellations; a contrail passing through the lunar halo, all at once! What an experience it was to be able to see these!” Thank you, Soumyadeep!
lunar halo emerges
Eliot Herman wrote on May 5, 2018: “This shows the change that occurred over 7 minutes as a lunar halo emerged. It then persisted for about 40 minutes and disappeared with increasing clouds. Although it appears the halo is forming from an odd shape, what is actually illuminated is the edge of the clouds just before the halo formed as the clouds drifted in front of the moon. But it does have a nice illusion of an odd-shaped halo then becoming round.”

Thank you to all who submit images to EarthSky Community Photos! View community photos here. We love you all. Submit your photos here.

Bottom line: High, thin cirrus clouds drifting high above your head create the halos you see around the sun or moon. The halos are from tiny ice crystals in Earth’s atmosphere. They do it by refracting and reflecting the light. Lunar halos are signs that storms are nearby.

March 31, 2023

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