Wikipedia:Reference desk/Archives/Science/2018 January 4

= January 4 =

22° halos
I know that 22° halos are supposed to be very common, but I have never seen one. I have seen rainbows every now and then. I want to know how I can easily spot 22° halos. I assume that if I spot a halo, it will be a 22° halo, as other types are much more rare.


 * I live in northeastern Massachusetts. Based on what I've read, this part of the world seems like a good spot to find halos. Is it?
 * Do time of day, time of year, and temperature matter?
 * In an open sky, seeing the halo means looking close to the sun, which causes a reflex to immediately look away. However, can I position myself so that the sun itself is blocked by a building, and I can still see the halo?
 * How long do halos last? If I was to go outside tomorrow (there is a blizzard today), how likely am I to see a halo, and how many hours should I wait before checking again if there isn't one?

HotdogPi 15:18, 4 January 2018 (UTC)
 * It's all about the weather. I don't know about MA (or how close you are to the coast), but the dry winters of the continental US are generally good. Our article here even shows one from Salem. You need to have the right sort of high altitude ice crystals, with cold, nearly still, clear skies. I've only ever seen them really well when high in the Alps. As being cold helps, they're sometimes more easily seen at night, around the Moon. All the UK ones I've seen have been Moon halos. Andy Dingley (talk) 15:59, 4 January 2018 (UTC)


 * This way cool site has an explanation. Be careful, you could spend hours looking at these pics!--TammyMoet (talk) 18:17, 4 January 2018 (UTC)


 * I've only seen a few true 22° halos, but sun dogs are more plentiful and, as 22° optical phenomena themselves, frequently are associated with halos. You can still see the halo if the sun is blocked by a building, but that is probably not necessary; they're not as close as photos suggest. Matt Deres (talk) 18:29, 4 January 2018 (UTC)


 * 22° halos are not particularly rare, I've seen a few examples last summer (July, August). In my Cfb climate (Netherlands) they're most common in summer, but your Dfa or Dfb climate may be different. I understand you occasionally have sunshine in winter. They're most likely in cirrostratus clouds, which usually precede a warm front, so pay attention to weather maps or satellite images. A warm front shows as a broad band of clouds with a fuzzy leading edge. Whenever you see cirrus or cirrostratus, look for halos. Having dense air traffic also helps (unfortunately). Those things blow a lot of water and cloud seeds into the upper troposphere, creating cirrus aviaticus, which later in the day may transform into cirrostratus. 22° halos can occur at any time of day (or night, around the moon), but in my experience they seem a bit more common in late afternoon, when the sun is lower and there are more aviation-induced clouds. They tend to be visible for an hour or so, maybe two. PiusImpavidus (talk) 12:01, 5 January 2018 (UTC)