Home / Weather News /

Trick of light: What is a circumzenithal arc?

15:00
21 May 2022

Trick of light
What is a circumzenithal arc?

Rainbow arcA circumzenithal arc captured in Powys, Wales last year. - © Jacqui Parsons

An optical phenomenon known as a circumzenithal arc is often sent in to us, do you know what they are?

The effect is the result of refraction of the sun’s light hitting ice crystals suspended in the atmosphere rather than hitting raindrops which creates the traditional rainbow.

This type of halo is also called a circumzenithal arc. However, it only occurs when the sun is no higher than 32° above the horizon. Circumzenithal arcs are not rainbows, because rainbows are caused by water droplets.

These arcs are not particularly rare but can be easily missed due to their appearance high in the atmosphere.

A very similar phenomenon are circumhorizontal arcs, where a coloured band of light runs parallel to the horizon.

If you spot any of the more than 50 types of arcs, or a traditional rainbow, be sure to snap a photo and send it to us using our dedicated image uploader.

Ryan Hathaway
More on the topic
Tuesday 1 July 2025

Captured by you

June in pictures
Thursday 26 June 2025

National parks and coasts

Isolated wind warnings in places
Sunday 6 July 2025

Your weather - Your shots

Shining summer clouds light the night
All weather news
This might also interest you
Wednesday 2 July 2025

Breakfast brief

Cooler with stormy potential
Monday 30 June 2025

Take precautions

Heatwave takes grip once again
Wednesday 2 July 2025

Isolated strikes here

Storms across Europe mostly miss UK
All articles
Weather & Radar

www.weatherandradar.ie

facebooktwitteryouTubeContact uslinkList
Privacy Policy | Legal info | Accessibility statement