What causes a ring or halo around the Moon?

What causes red rings to appear around the moon? - Quora

Astronomy for beginners BBC Sky At Night Magazine

Why Texans saw a weird ring of light around the moon

How is it possible that one state in the country witnessed the lunar halo but other states didn't? - Quora

ဘာ့ကြောင့် လထီးဆောင်း တာလဲ – Myanmar Scientist

Did YOU see a 'halo' surrounding the moon last night?

What causes a ring or halo around the Moon?

Social media users share delight after capturing 'halo' around moon

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Why a ring formed around the moon last night near Youngstown, Ohio.

Why you saw a halo around the moon last night

What causes a ring or halo around the Moon?

How is it possible that one state in the country witnessed the lunar halo but other states didn't? - Quora