Understanding Sun Halos: Causes, Types, and Safety Tips

A photo I took of a solar halo.

I only saw my first sun halo recently. I was walking down the street and a girl on a motorbike came to sudden stop, whipped out her phone and pointed it at the sky. As I walked past she excitedly said “Can you see the rainbow?”. Now I love rainbows as much as the next person, so I excitedly looked up and subsequently blinded myself by looking at the sun. But once I applied my non-recommended “safety squint” technique I realised that there was an amazing halo around the sun.

What is a sun halo?

A sun halo is a ring of light that appears around the sun. It is caused by the refraction of sunlight through ice crystals in the atmosphere. The ice crystals are typically found in high-altitude cirrus clouds.

When sunlight hits an ice crystal, it is refracted, or bent, in different directions depending on the angle of incidence. The different colors of light are refracted at different angles, which is why the sun halo appears white in most cases. However, if the ice crystals are oriented in a certain way, the colors of the rainbow can be seen.

A diagram showing how sunlight refracting off ice crystals create sun halos
Sunlight is refracted by ice crystals to form a halo around the sun

A sun halo can be unique to the observer as it changes depending on the level of the observer’s eyes.

What are the different types of sun halos?

There are several different types of sun halos, each with its own unique appearance. The most common type is the 22-degree halo, which is a white ring that appears around the sun. Other types of sun halos include the sundog, which is a bright spot of light that appears on either side of the sun, and the upper tangent arc, which is a faint arc that appears above the sun.

Safety tips for viewing sun halos

It is important to never look directly at the sun, even if there is a halo around it. The sun’s rays can damage your eyes. If you want to see a sun halo, you should use indirect viewing methods, such as looking through a piece of smoked glass or by projecting the image of the sun onto a white surface.

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