This evening there is an unusual halo around the Moon. I have seen lunar halos many times before; they are about 22 degrees across. This is *much* larger. Can anyone else in the San Francisco Bay Area, or northern California see this? Michael

Is it this that you are talking about Michael?

http://apod.nasa.gov/apod/ap000515.html

Is it this that you are talking about Michael?

http://apod.nasa.gov/apod/ap000515.html

make clicky

That's a fine picture of a 22 degree-wide Lunar halo. The one I saw last night was over twice as big as that. I looked at many pictures of lunar halos on the internet. All were about 22 degrees wide. Larger ones are apparently quite rare, which is why I posted about it. Lunar halos are usually associated with full Moons. Last night's Moon was about half. Michael

Even my little star book that I received about 1953 said that in addition to a 22-degree lunar halo there can be a 46-degree one. I believe it's just ice crystals or possibly water droplets in the atmosphere. I believe they forecast rain within 12 to 24 hours.

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Have now looked at over 500 images of Lunar halos. Found four that show the double-sized, or 46 degree widths. That works out to something under 1 chance in 100 of seeing the larger variety, rather than the smaller. They could be rarer than than, of course. It is reasonable to suppose that the unusual, larger halos are more likely to be photographed and reported than the smaller, more common sort. If so, the larger are over represented in my sample, making them appear more common than they actually are. Michael