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Misnomer Majestica: Fire Rainbows

So-called Fire Rainbows actually have nothing to do with fire or rainbows, however they are absolutely awesome! The correct nomenclature for this optical phenomenon is circumhorizontal arc (circumhorizon arc and lower symmetric 46° plate arc are also accepted). A multi-colored halo (spanning from the red wavelengths at the top to the indigo like a rainbow) that runs parallel to the horizon occurs when the sun’s height in the sky is more than 58° above the horizon and its light passes through a cirrus cloud or haze consisting of ice crystals. These ice crystals must be hexagonal and plate-shaped, facing parallel to the ground. When light enters the top of the ice crystal through its vertical side face, and exits bending through the lower horizontal face, it separates like a prism.

While the circumhorizontal arcs are indeed arcs, they frequently only appear in small sections of wispy cirrus clouds where the ice crystals are properly aligned, which leads to the misnomer “fire rainbow”. Here’s a small gallery of this spectacular optical phenomenon:

Midnight Sun

Our sun is absolutely astounding, and that’s no news, especially for JOL readers. However, the grand winner of a National Geographic exploration trip through X Prize, Joe Capra, entered with a stunning video about our home star’s polar seasonal effects so delightfully, I had to share.

In areas north of the arctic circle or south of the antarctic circle, in summer months the sun can be visible for up to twenty-four hours of the day, sinking but never dropping below the horizon line. This is similar to the effect of “white nights” where latitudes as low as sixty degrees experience midnight twilight, though in white nights the sun does go below the horizon line. In his film’s narration, Mr. Capra speaks about how because of the midnight sun effect, he had almost six hours between sunset and sunrise of low-level light to shoot.

Check out Mr. Capra’s video, “Land of the Midnight Sun” (RSS readers, please click through!):

A beautiful video on the opposite effect, polar night, Jim shared here.

What is The “UV Index,” and Why Should I Care?

I was driving earlier this morning through Ontario on my way to Buffalo for a flight, and the sky was clear and cloudless.  It’s a little on the chilly side up there in the Buffalo area (at least it was at 7am when I was on the road), but on the CBC News I heard an anchor talk about a “very high UV index that will make being outside a little on the burny side.”

What?  I’m going to Dallas right now on a flight, and the UV Index is something that I’ve always just assumed was because we’ve polluted a hole in the ozone, and Nicolas Cage is going to have to deal with aliens like he did in that horrible movie about the sun burning up the Earth.

So what exactly IS the UV Index, how does it affect us, and why should we care?

Well, have you ever been sunburned?  How about melanoma?  Ever had a skin cancer scare?  Sun poisoning?  Blisters?  It’s the ultraviolet rays of the sun’s radiation that make our skin the color of a lobster when we’re out in it.  Did you know that overexposure to the sun can cause cataracts?!

Yeah.  I still love the sun.  That’s probably why I’ll look like a freaking leather catcher’s mitt when I’m 50.

There are three types of ultraviolet radiation:

  • UVA – makes it through the ozone layer
  • UVB – mostly absorbed by the ozone layer; some does reach the Earth’s surface
  • UVC – completely absorbed by the ozone layer and oxygen

Our Environmental Protection Agency has quantified the risk of the amount of UV exposure that we get on a certain day.  From the EPA’s website on sun exposure:

and something a little more helpful, from Wikipedia:

UV Index Description Media Graphic Color Recommended Protection
0–2 No danger to the average person Green Wear sunglasses on bright days; use sunscreen if there is snow on the ground, which reflects UV radiation, or if you have particularly fair skin.
3–5 Little risk of harm from unprotected sun exposure Yellow Wear sunglasses and use sunscreen, cover the body with clothing and a hat, and seek shade around midday when the sun is most intense.
6–7 High risk of harm from unprotected sun exposure Orange Wear sunglasses and use sunscreen having SPF 15 or higher, cover the body with sun protective clothing and a wide-brim hat, and reduce time in the sun from two hours before to three hours after solar noon (roughly 10:00 AM to 4:00 PM during summer in zones that observe daylight saving time).
8–10 Very high risk of harm from unprotected sun exposure Red Wear sunscreen, a shirt, sunglasses, and a hat. Do not stay out in the sun for too long.
11+ Extreme risk of harm from unprotected sun exposure Violet Take all precautions, including: wear sunglasses and use sunscreen, cover the body with a long-sleeve shirt and trousers, wear a very broad hat, and avoid the sun from two hours before to three hours after solar noon.

I guess that extra four hours a day in the sun over a period of 30 years wasn’t so good for me after all, huh!

When you’re outside this summer, do yourself a favor, wouldja?  Put on some sunscreen!  I’m certainly not one to advocate for staying out of the sun – it’s my favorite source of light after fire!

Thanks, Dermis.net and J Grundy!