Predictions & The Science Of Rainbows

22 degree halo with Sun Dogs, January 11, 2011 3:08pm (sunset 4:20)

These photos were all taken on January 12th. Clockwise from left, Northern cardinal, White-throated sparrow and Song sparrow. Birds have to eat regardless of the weather. These two sparrows have been together at my feeders all winter. I can predict that when I see one, momentarily I will see the other.

22 degree parhelic arc photographed January 11, 2011

"You don’t need a weatherman to know which way the wind blows."                   
                                                                                            Bob Dylan

      The night before our last whopper of a snow storm, I took these photographs of 'rainbows' in the late afternoon sky. For days, the weather forecasters had been predicting a storm, but they could not say how bad it was going to be. Repeatedly, they sited computer models that just weren't reliable for what the satellites showed moving across the country. They thought we'd get six inches or less which for us is nearly a non event. While out and about, I first noticed the most westerly of these color patches in the sky which prompted me to keep looking upward. As I went in and out of buildings and my car while travelling about fifteen miles, the patch persisted. That's when I noticed at the same time, a second, odd rainbow further east. Sunset was then less than an hour and half away making it quite dark. But, I was compelled to photograph the phenomenon. These disturbances in the sky made me uneasy. I announced to my husband "Those weathermen should just stick their heads out of the window instead of relying on computer models. If they saw those two weird rainbows, they'd know all hell's going to break lose."
     The next day, before it was all said and done, we had fifteen inches of snow. Two days later, I saw another one of  the colorful patches in the sky. No snow was predicted at all, but before nightfall we did have a dusting that covered everything. Oh, if only everything were that simple to predict!
     I'm impatient with forecasters. Having been hit with a big weather stick after their last laizzes faire prognosticating, I'll be bored and ultimately unprepared when  an inevitable round of their histrionic prattling proves accurate. After all, this is Maine and it is winter. One of these days, after they've said so, we will be hit with another big one. Nonetheless, I should lighten up on the weather guys; meteorologists do get it right more often than wrong. And, weather is trickier to predict than what we want to think. With low tolerance for inconvenience and jam packed lives, most of us need tidy means for planning our affairs right up to the last minute. Often unrealistically, we expect science to provide and meteorology is not the only science that fails us. The predictions of medical science don't always pan out, either. 
     For nearly six days, my centenarian grandmother was in a coma. She did not drink nor eat nor respond.  The doctor called from the nursing home. "I'm afraid your grandmother is in heart failure. It won't be long. She's had a long fight." Expecting her to die any moment, hospice services were put into play.  I cried. I met with the hospice worker. I signed papers. I cried some more. I talked to my grandmother, though it felt like talking to nothing and nobody anymore, a piece of firewood. I told her it was okay to die, that she could let go and stop struggling. I sat beside her for hours every day doing nothing but being there. Finally, on the evening of day six, I decided to go home. I bent down and kissed her forehead. I told her "Grandy, I'm going home. I'll be back. I love you."
     Suddenly, her eyes flew wide open. Smiling broadly, my totally blind grandmother looked  right at me clear-eyed and said "Thank you! Is it raining?" "Raining?" I asked. "Yes, rain-ning" she enunciated, as if my bewildered response was born of stupidity. In the next fifteen minutes she  drank half a cup of tea and ate most of a cheap, molasses donut, her favorite. Now, three days later, she's still chatty, up every day, and dressed. The weatherman got it really wrong this time. But, one of these days............
   Greek mythology held that rainbows were paths from Earth to Heaven and the Norse believed that rainbows connected the realms of  the gods and humans. Irish leprechauns hid pots of gold in the secret place at the end of the rainbow. A rainbow is an optical effect which depends on the location of the viewer, so the end of a rainbow is impossible to reach. When walking towards the end of a rainbow, it will appear to move further away. Two people simultaneously observing  a rainbow from different locations will disagree about where a rainbow is. Rainbows have a place in legends owing to their beauty and historically, the difficulty in explaining the phenomenon.
     Rainbows aren't simple; what we see in the sky that we call a "rainbow" may not be a rainbow at all. A rainbows is  produced by the refraction of sunlight going into and coming out of raindrops, with reflection of the light inside the drops. The optical effect of the rainbow forms when sunlight enters a raindrop, slows, then bends (refraction). Light travels in waves of energy and appears white due to the combination of colors in that single wave of energy. When light bends individual colors separate. Violet light refracts the greatest and red light refracts the least. A rainbow is visible to us when the different colored light waves reflect on the walls of the water drops. This is the simplest explanation and the most common form of what we think of as a rainbow. But, light travelling through water in the atmosphere can also create circles, ovals, arcs, spots, pillars, and crosses.
     All the colored patches or atmospheric optical phenomena we see in the sky aren't rainbows, though single rainbows are the most common followed by double rainbows. When the sun is high in the sky, we may see the bottom of  a circumzenithal arc, a fascinating atmospheric phenomenon, sometimes called a reverse rainbow. It resembles a backwards or upside-down rainbow which looks like a heavenly smile. Rainbows even happen at night!
     What we see for atmospheric optical phenomena varies with the angle of the light source, usually the sun, and atmospheric conditions - fog, clouds or rain. Some form of water in the atmosphere  is necessary for the prismatic phenomenon to occur, but not necessarily rain or even bad weather. Colored arcs, bands, and smudges are also created by ice crystals. "Diamond dust" refers to ground level fog which forms ice crystals at very low temperatures. White light bounced off the crystal faces slows down and separates making the colors visible, sometimes as a band on a level plain parallel to the horizon.
     The classic rainbow arc is always seen opposite the sun, while halos encircle the sun (or moon, but that's another story). Rainbows are always water and halos are always ice crystals. We may not be able to see the whole of a rainbow's arc or the complete circle of a halo, giving the appearance of a patch of color.
     The most common halo is a 22 degree circle around the sun. I'm pretty sure that the photographs above are parts of a  22 degree halo, though I'm not positive. There is also a Sun dog or Parhelia  (the very bright light in the top photo). Sun dogs are red colored towards the sun and sometimes have greens and blues beyond. True rainbows have a reverse color order from Sun dogs.  Sun dogs can be blindingly bright, even brighter than rainbows. At other times they are a mere colored smudge on the sky. They are visible all over the world and at any time of year regardless of the ground level temperature. They often appear as a pair on opposite sides of the sun. These Parhelia or Mock Suns, are with the 22º halo, the most frequent of the ice halos. Whether Sun dogs are visible versus a 22 degree halo is simply a result of which direction the ice crystals are facing. They are most easily seen when the sun is low.
     I saw an odd rainbow in the sky. It seemed so simple. But, after hours of research and study, I'm still not sure what it was. The rainbow business is far more complicated than I would ever have guessed, like weather forecasting and steps toward death. There just aren't good computer models, light bends and the path to the end is not linear. My grandmother is still looking for the end of her rainbow.

Rainbow vocabulary:

1. Rainbow

2. 22 degree halo (common)

3. 46 degree halo (very rare)

4. cirumzenithal arc or reverse rainbow

5. circumhorizon arc or lower symmetric 46° plate arc

6. Supralateral & Infralateral arcs 

7. tangent arc
8. Sun dog

9. Diamond dust

10. The End

For more information on atmospheric optics and rainbow variations with great photographs, click on any of these links:

http://www.wisegeek.com/what-are-sun-dogs.htm

http://www.atoptics.co.uk/halo/supinf.htm

http://haloreports.blogspot.com/

http://optics.kulgun.net/Observing/

http://www.ursa.fi/blogit/ice_crystal_halos/index.php

This is a Skywatch Friday post. Check out what other people saw on Friday!