How does light pass through the crystals?

In through a side face and out the bottom face

Where does the arc appear?

Below the Sun, parallel to the horizon

Circumhorizontal Arc Quiz: The Fire Rainbow Explained

This circumhorizontal arc quiz looks up at a band of rainbow colors stretched across thin clouds. Play 10 interactive questions on plate-shaped ice crystals in cirrus clouds, light entering a side face and leaving the bottom, why the Sun must be high in the sky, the arc running parallel to the horizon below the Sun, the misleading nickname fire rainbow and when and where they appear.

Start Circumhorizontal Arc Quiz

🎯 Daily Trivia Challenge • 🧠 10 Questions • ⏱️ 150 Seconds

Question 1 / 10 Time: 150s

Type
What kind of optical effect is a circumhorizontal arc?
Crystals
Which crystals make it?
Clouds
In which clouds does it usually appear?
Path
How does light pass through the crystals?
Sun
How high must the Sun be?
Position
Where does the arc appear?
Nick
What is its misleading nickname?
Season
When is it most common at mid-latitudes?
Colors
Which color is usually on top?
Cousin
Which halo appears above the Sun with the same crystals?

Explanations: answer key for all 10 questions

Q1: What kind of optical effect is a circumhorizontal arc?
Answer: An ice halo
Ice crystals cause it.
Q2: Which crystals make it?
Answer: Flat, plate-shaped ice crystals
They float horizontally.
Q3: In which clouds does it usually appear?
Answer: Thin cirrus clouds
They are high and wispy.
Q4: How does light pass through the crystals?
Answer: In through a side face and out the bottom face
This bends light strongly.
Q5: How high must the Sun be?
Answer: More than about 58 degrees above the horizon
So it appears near midday in summer.
Q6: Where does the arc appear?
Answer: Below the Sun, parallel to the horizon
It lies flat across the sky.
Q7: What is its misleading nickname?
Answer: Fire rainbow
It involves neither fire nor rain.
Q8: When is it most common at mid-latitudes?
Answer: In summer around midday
The Sun climbs high then.
Q9: Which color is usually on top?
Answer: Red
Colors run horizontally.
Q10: Which halo appears above the Sun with the same crystals?
Answer: Circumzenithal arc
It forms when the Sun is low.

The So-Called Fire Rainbow

A circumhorizontal arc is an ice halo, a band of rainbow colors stretching across thin cirrus clouds. It forms when sunlight passes through flat, plate-shaped ice crystals floating horizontally. Light enters through a vertical side face and leaves through the bottom face, bending strongly and splitting into colors.

The Sun must be more than about 58 degrees above the horizon, so at mid-latitudes the arc appears mostly in summer around midday. It lies below the Sun, running parallel to the horizon, usually with red on top.

It is often called a fire rainbow, a misleading nickname since it involves neither fire nor rain. When the Sun is low, the same crystals can create the circumzenithal arc, a smile-shaped bow high above the Sun.

What This Quiz Teaches

Sky fans will enjoy these questions.

What the arc is
Which crystals form it
How light travels
When it appears
Why its nickname is wrong

Did You Know?

It can look like colored flames in clouds.
Only parts of the arc may show.
Viral photos often mislabel it.
Polarized sunglasses can change its look.
It is wider than a rainbow.