Why do they glow after sunset?

They are high enough to catch sunlight

Noctilucent Clouds Quiz: Glowing Ice at the Edge of Space

This noctilucent clouds quiz looks to the twilight sky on a summer night. Play 10 interactive questions on the highest clouds on Earth, around 80 km up in the mesosphere, ice crystals forming on meteor dust, why they glow after sunset, summer viewing at higher latitudes, their first reports after Krakatoa in 1885, NASA's AIM satellite and links to rocket exhaust and climate.

Start Noctilucent Clouds Quiz

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

Question 1 / 10 Time: 150s

Name
What does noctilucent mean?
Height
About how high do noctilucent clouds form?
Layer
In which atmospheric layer do they form?
Made
What are noctilucent clouds made of?
Seed
What do the ice crystals often form on?
Glow
Why do they glow after sunset?
Season
When are they usually seen?
Where
At which latitudes are they best seen?
First
When were they first widely reported?
Satellite
Which NASA mission studies them?

Explanations: answer key for all 10 questions

Q1: What does noctilucent mean?
Answer: Night-shining
They glow after dark.
Q2: About how high do noctilucent clouds form?
Answer: Around 80 km
They are the highest clouds.
Q3: In which atmospheric layer do they form?
Answer: The mesosphere
It is extremely cold.
Q4: What are noctilucent clouds made of?
Answer: Ice crystals
They form in very dry air.
Q5: What do the ice crystals often form on?
Answer: Meteor dust
Space dust provides seeds.
Q6: Why do they glow after sunset?
Answer: They are high enough to catch sunlight
Lower clouds are in shadow.
Q7: When are they usually seen?
Answer: In summer
The mesosphere is coldest in summer.
Q8: At which latitudes are they best seen?
Answer: Roughly 50 to 70 degrees
Northern Europe and Canada are good.
Q9: When were they first widely reported?
Answer: 1885, after Krakatoa erupted
People watched twilight skies closely.
Q10: Which NASA mission studies them?
Answer: AIM
It launched in 2007.

Clouds at the Edge of Space

Noctilucent, meaning night-shining, clouds are the highest clouds on Earth, forming around 80 km up in the mesosphere. They are made of ice crystals that often form on tiny particles of meteor dust in the extremely cold, dry air.

After sunset, lower clouds fall into shadow, but noctilucent clouds are high enough to still catch sunlight, glowing electric blue against the twilight sky. Surprisingly, the mesosphere is coldest in summer, so they are seen in summer, mostly at latitudes of roughly 50 to 70 degrees, such as northern Europe and Canada.

They were first widely reported in 1885, two years after Krakatoa erupted, when people watched twilight skies closely. NASA's AIM satellite, launched in 2007, studies them. Water vapor from rocket exhaust and changes linked to climate may be making them more common and visible farther south.

What This Quiz Teaches

Sky fans will enjoy these questions.

What they are
How high they form
Why they glow
When to see them
How they are studied

Did You Know?

They show rippling wave patterns.
Photographers stay up late to catch them.
They can be seen from space.
Methane breakdown adds water vapor.
They are also called polar mesospheric clouds.