Thursday, January 16, 2014

Somewhere "Over" the Rainbow


Somewhere "Over" the Rainbow
Brian and Tyler-Marie and I were out at Sunset Bay enjoying a beautiful calm sunny afternoon, tide-pooling and collecting marble size concretions.
Collecting this unusual rock is "phenomical" all in itself...but that afternoon we were treated with a more unusual work of nature. High above the sky we discovered an "upside-down" rainbow. It was very bright and extremely beautiful.
This phenomenon is called a circumzenithal arc...(CZA) A circumzenithal arc is a fascinating atmospheric phenomenon, sometimes called a reverse rainbow, because at first glance it does indeed resemble a backwards or upside-down rainbow. Many observers miss out on circumzenithal arc's, because they are located directly overhead. Unlike a rainbow, which appears opposite the sun, a circumzenithal arc is centered around the zenith of the sky, and can only appear if the solar angle is less than 32 degrees. In order for conditions to be right for a circumzenithal arc to form, small, flat, six sided ice crystals must be suspended high in the sky to create a field of tiny prisms. The sun's rays enter the ice crystals and reflect through them, projecting an arc in the sky.
The circumzenithal arc will remain until the solar angle changes, unless weather conditions change dramatically. The colors of a circumzenithal arc are also reversed from those of a rainbow; the violet end of the spectrum is closer to the zenith of the sky, while the red range is closest to Earth. Technically, the red range is still at the top of the arc, but because the arc is reversed, the colors seem upside down as well. When looking at a circumzenithal arc.In most cases, a circumzenithal arc will last at least half an hour, and sometimes more, plenty of time to admire and photograph the beautiful phenmonon. They are most common in colder climates, where ice crystals tend to collect in the sky with abundance, although they can be seen in temperate zones as well, especially during cooler weather. This photo was taken in Grand Forks, North Dakota on January 31st 2007 If circumzenithal arc phenomenon wasn't enough that day, we were also treated with a parhelic Circle. The parhelic circle can be an impressive white arc spanning 360 degrees in azimuth...(the point where a vertical circle through a given heavenly body intersects the horizon)...when complete, running through the sun, the two 22o parhelia. It is parallel to the horizon, and at the same elevation as the sun. In this photo, it looks like the sun is visible within the ring. Brian is looking at the CZA...the sun is directly in front of him. The round white sun-like "sun" in this photo is a reflection of the real sun within the Parhelic Circle. There were three reflections visible; one south, east and north...and of course the real sun was west.
The parhelic circle is caused by sunlight reflecting from the vertical faces of horizontally aligned, plate-like ice-crystals. Sometimes, the arc can also be colored, in the anthelion area.
A great day for the Heaven's to present nature at its best.

2 comments:

Tranquility said...

Oh my goodness! Incredible!
I didn't know these sky beauties existed - lucky you to see them both (and with a camera in hand too)!

christyzee said...

Very, Very cool! Thank you so much for sharing!
Blessings...