View Full Version : Moon Halo

2003-Jan-17, 10:53 AM
Tonight at work, I happened to look up into the sky at the moon, as I often do, and I noticed that there was a halo around it. I didn't notice it right off, because of it's sheer size. I've seen halos around the moon before, and usually, they're between 2 and 5 times the size of the moon. Tonight, it was more like 20-25 times the size of the moon. Just out of sheer curiosity, what causes the moon halo, and what would make it appear to be so huge tonight when I normally see it as being much much smaller?

2003-Jan-17, 11:02 AM
The moon looks bigger on the horizon?? /phpBB/images/smiles/icon_smile.gif

2003-Jan-17, 11:05 AM
/phpBB/images/smiles/icon_smile.gif Nice try, GoW, but the moon was near it's zenith when I noticed it. I wouldn't have even noticed if I hadn't have thought about what the BA said in his book about holding a dime almost 2 meters away before it was the same size as the moon. (Yes, I tried it. At arm's length, it completely covered the moon.) That's when I noticed that there was a relatively huge halo around the moon. BTW, about 6 hours later, it fogged up pretty badly.

2003-Jan-17, 11:41 AM
I meant, when you saw it before. /phpBB/images/smiles/icon_smile.gif

Here is a site about lunar halos (http://home.hiwaay.net/~krcool/Astro/moon/moonring/). It says that the halo made by ice crystals is usually around 22 degrees in diameter, which would be around forty times the size of the moon.

2003-Jan-17, 11:49 AM
*shrug* Maybe I had my measurements wrong. It certainly appeared to stretch more than 22 across the horizon, so maybe I got lucky and saw a 44 halo? Who really knows... I did point it out to a few of my friends at work, and a couple of them called it "monstrous". It was quite a sight, though. I only wish I'd have had a camera that could have produced a photo that would have done the moment justice.

2003-Jan-17, 12:11 PM
On 2003-01-17 05:53, Jetmech0417 wrote:
Tonight, it was more like 20-25 times the size of the moon.
That would be 10 to 12 degrees.

On 2003-01-17 06:49, Jetmech0417 wrote:
Maybe I had my measurements wrong. It certainly appeared to stretch more than 22 across the horizon
22 degrees would be over forty times the size of the moon. Something is wrong. /phpBB/images/smiles/icon_smile.gif

2003-Jan-17, 12:14 PM
Oops. Typo. Meant to say "more than 22 across the sky".

David Hall
2003-Jan-17, 12:58 PM
I used to see giant halos in all the time in East Texas. I was always amazed at their size and beauty. I just loved them. Must be something about the conditions in that area, 'cause I've never seen ones like that elsewhere.

I saw a small halo around the Moon here about a <strike>week</strike> month ago though.

Edit: I just remembered, I saw a nice full Moon this evening, so it must have been over a week ago. Make that one lunar month ago. /phpBB/images/smiles/icon_smile.gif
...And that, my liege, is how we know the Earth to be banana-shaped. --Sir Bedevere

<font size=-1>[ This Message was edited by: David Hall on 2003-01-17 08:11 ]</font>

2003-Jan-17, 01:07 PM
On 2003-01-17 07:58, David Hall wrote:
I used to see giant halos in all the time in East Texas.
Of course! Everything is bigger in Texas. /phpBB/images/smiles/icon_biggrin.gif

2003-Jan-17, 01:14 PM
I remember seeing a huge halo around the moon a few months ago, when I was living in northern West Virginia. I called my wife outside to see it. It was breath-taking! It appeared to be about twice the diameter of most halos I have seen.


2003-Jan-17, 01:18 PM
We were out stargazing with the astronomy club and seeing was poor--there was a bright halo around a bright moon. Everyone was remarking about how large the halo was. It was a 22 degree halo.

2003-Jan-17, 06:44 PM
*shrug* Who knows? Maybe it was just my sense of perception last night. But, to me, at least, the halo appeared to be HUGE.

2003-Jan-17, 07:10 PM
I love a good Moon halo like that.... and remember that Jupiter subtends almost that much of the sky (19ish degrees v. 22 degrees) from the surface of Io. Imaging seeing -that- in person.

2003-Jan-17, 07:30 PM
On 2003-01-17 13:44, Jetmech0417 wrote:
*shrug* Who knows? Maybe it was just my sense of perception last night. But, to me, at least, the halo appeared to be HUGE.
I curious about that sense of perception. What did you mean in your original post when you said that the one last night was 20-25 times the size of the moon?

2003-Jan-17, 07:35 PM
That was a simple estimate. I didn't actually measure it or anything. Thinking back, it may have been larger than that, but I'm not really sure. I wish I could have gotten a picture of it. Then I could post it or email it to people who want to see it. But, sadly, I didn't. There's nothing saying that I didn't overestimate, OR underestimate. Sorry if I'm creating a lot of confusion.

2003-Jan-17, 07:41 PM
My point was that even if the halo was double your estimate, it would still only be 22 degrees. Your estimate was 11 degrees--small.

But they do look huge.

2003-Jan-18, 01:48 AM
I agree with you. I was thinking about it on the way home tonight, and it looked huge, but thinking about it, it was nowhere near 44. The longer I thought about it, the better I visualized it in my mind, and it was probably 22.

The Bad Astronomer
2003-Jan-18, 04:51 AM
Besides the 22 degree halo, there can be a halo immediately around the Moon. I believe this is also caused by ice crystals, and they can refract the light, giving the halo some color. I have seen this same effect at the edges of clouds, turing them pink or even greenish. The first time I saw that I thought I was losing my mind. /phpBB/images/smiles/icon_smile.gif

2003-Jan-18, 05:41 AM
Now, that, I've seen before. I've seen a halo very close to the moon a fair amount of times, but I don't ever remember seeing one this big before. I was thinking about asking about it, but I wasn't sure how to phrase it. Thanks, BA.

2003-Jan-18, 05:11 PM
My brother and I saw an amazingly clear moon halo the other night too, out here in Arizona. We saw the bright close disk-like halo around the moon, and also the the 22 halo. We put our pool chairs in the laid down position and lay staring up at it discussing our theories about the mechanism of it's projection. We came up with ice crystals, but couldnt figure out why they made a halo instead of a solid disc of light. We thought maybe it had to do with the angle of the crystals so that only the the 20-22 range from the viewers point-of-view reflects light significantly...all other points the light is either too dim in reflection or passes straight through the crystals without scattering...or something along those lines anyways...

Dont ask me about math...I'm an artist...I just like looking up at all the pretty lights... /phpBB/images/smiles/icon_wink.gif

<font size=-1>[ This Message was edited by: Comixx on 2003-01-18 12:12 ]</font>

2003-Jan-18, 09:28 PM
About a year ago (it was very cold) I saw a double halo around the nearly full moon. The halo at 22 degrees was very bright and showed some color and there was a much larger and much dimmer halo visible as well. It was the best lunar halo I have ever seen, I even made my wife and daughter put on their coats and come outside to see it. They aren't nearly as interested in astronomical phenomena as I am (we all know about that, right?) but they were pretty impressed by that display.

2003-Jan-18, 09:29 PM
That lunar halo link calls the smaller disk halo a lunar corona.

David Hall
2003-Jan-19, 09:18 AM
Been thinking about it, and yes, the ones I used to see were the 22&deg; ones. The thing is, it's really hard to get an accurate sense of scale in the sky. Things tend to look much larger than they actually are, like the Moon illusion.

Other examples: the height of Orion is only 16&deg; and the Big Dipper is about 25&deg; from end to end.

The smaller one I saw last month must have been a lunar corona, as Grapes pointed out. However, lunar coronas seem to have a surprisingly solid ring shape, unlike the more famous solar corona, so calling it a "ring around the moon" is not really much of a misnomer.