# What was that halo around the moon? **URL:** \ **Category:** Factual Questions\ **Created:** [April 25, 2003, 12:55am UTC](https://boards.straightdope.com/t/what-was-that-halo-around-the-moon/170996 "2003-04-25T00:55:11Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![Fuel](https://avatars.discourse-cdn.com/v4/letter/f/df705f/32.png) [@Fuel](https://boards.straightdope.com/u/Fuel)\ **Post date:** [April 25, 2003, 12:55am UTC](https://boards.straightdope.com/t/what-was-that-halo-around-the-moon/170996/1 "2003-04-25T00:55:11Z")
A week or two ago, my friend pointed out to me this HUGE halo around the moon. _This halo was very dull and very thin_, but it travelled in a perfect circle around the moon and was MUCH MUCH BIGGER than the moon itself, as in, far away from the outline of the moon with a much larger diameter. It was a fairly clear and cool night here in Central Florida, the way most nights are. The moon was close to straight over head, maybe 5-10 degrees off top dead center, and it was about 10 o’clock at night. What was this halo and what caused it? My guess is light reflecting off a certain layer of the atmosphere, but why in this manner? Is it rare? ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [April 25, 2003, 12:57am UTC](https://boards.straightdope.com/t/what-was-that-halo-around-the-moon/170996/2 "2003-04-25T00:57:26Z")
You can see this all the time. Well, not all the time, but a lot of the time. Has something to do with what you said, and I’m sure someone smarter than me will show up shortly and explain the details. I’ve always heard it as an indication of a change in the weather (from good to bad as well as bad to good). ---
**Author:** ![AndrewL](https://avatars.discourse-cdn.com/v4/letter/a/3d9bf3/32.png) [@AndrewL](https://boards.straightdope.com/u/AndrewL)\ **Post date:** [April 25, 2003, 12:57am UTC](https://boards.straightdope.com/t/what-was-that-halo-around-the-moon/170996/3 "2003-04-25T00:57:57Z")
Ice crystals high in the atmosphere. A little of the light is bent a certain angle going through them, which creates the halo effect. It’s not all that rare, you just need the right atmospheric conditions. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [April 25, 2003, 1:02am UTC](https://boards.straightdope.com/t/what-was-that-halo-around-the-moon/170996/4 "2003-04-25T01:02:48Z")
It’s caused by atmospheric [ice crystals](http://antwrp.gsfc.nasa.gov/apod/ap000515.html).