What makes a halo around the sun or moon?

We tell you all you need to know about halos in our YouTube video here. Don’t forget to subscribe!

What causes halos?

Have you ever looked up and spotted a large ring of light around the sun or moon? Scientists refer to these as 22-degree halos. They got that name because the radius of the circle is always 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 unique halo, made by the ice crystals from their point of view. So they are different from the ice crystals making the halo of a person standing next to you.

large ring of light around the moon on a dark sky, with three trees in the snow in the foregroundfir
Goran Strand captured this beautiful image of a lunar halo in February 2021, from Östersund, Sweden. Notice that – unlike solar halos, which can be colorful – lunar halos are mostly colorless. Image via Göran Strand of Used with permission.

A word of caution for photographers

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 less bright through clouds or fog.

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.

Ice crystals seen as rectangles and hexagons in greyscale on a plain grey blackground, sized around 0.1mm.
Halos are made by both refraction and reflection ice crystals, such as these, in this photo by Walt Tate. Image via Walt Tate/ Atmospheric Optics. Used with permission.

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.

2023 halo photos from EarthSky’s Community

Greyscale image of a sun surrounded by a halo of light, with the branches of a blossoming tree in the foreground
View at EarthSky Community Photos. | Teresa Molinaro in Palermo, Italy, captured this halo image on May 17, 2023 and wrote, “Sun halo in the blossoms tree.” Thank you, Teresa!
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, with Mars, Pleiades and a few stars labeled.
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!

More halo photos from our friends

sun on a blue sky with a ring of light around it, and an outstretched finger overlapping the sun itself
Everyone sees his or her own halo. That’s because – for every individual – a solar or lunar halo is made of light reflecting and refracting from different ice crystals in high, thin cirrus clouds. Image via Vincenzo Mirabella in Italy/ NASA. Used with permission. Thank you, Vincenzo!
Fisheye view of whole sky with moon, faint ring, and labeled planets.
View at EarthSky Community Photos. | Meiying 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!
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!

And more halo photos from our friends

Multiple rings of light around the moon in hazily starry sky above palm trees.
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!
A halo around the bright 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!
3 fish-eye images of the whole sky with clouds and halo around the moon.
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.” Used with permission.

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.

May 31, 2023

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