A beautiful celestial display in the sky: the 22-degree solar halo

Today while driving to get some groceries, I had the opportunity to witness a beautiful and not so common phenomenon; a giant ring around the Sun. I was wondering about what it is but decided to stop at the side of the road and click some pictures. I googled the information  and came to  know about what  and  how these giant rings are formed.

Halos are rings of light that encircle the sun or the moon, and they occur when a thin layer of cirrus clouds are present at altitude of  20,000 feet or more above our heads.

The complete halo as seen from the island of Oahu, Hawaii.

What Causes Sun Halos?

Well, a mix of chemistry, physics and geometry explains the cause of formation of sun halos.

The cirrus clouds contains millions and millions of tiny ice crystals As sunlight passes through the ice crystals, the geometry of the crystals causes the light to refract and reflect similar to what happens when light passes through a prism. 

According to the University of Illinois at Urbana-Champaign, randomly-oriented hexagonal ice crystals with diameters less than 20.5 micrometers are responsible for the halo observed in the sky. This geometric size and shape causes light to undergo two refractions, or bends, as the light passes through the ice crystal. Once the second bend is made, the light appears as a halo in the sky.

The process works for any celestial light source, which means moon halos form under the same physical and geometrical properties. In addition, the process is similar to how rainbows are formed, which is why colors can sometimes be seen in the rainbow.

courtesy:http://www-das.uwyo.edu/

Scientist call it the ‘22-degree halos, because the two refractions bend the light by 22 degrees from its original direction. This means that the halo can be seen when your eye makes a 22 degree angle with the sun or moon.

love this capture, a plane flying towards the halo

The halo is fading now 

Halo causing illusion of inverted rainbow

Halo causing illusion of inverted rainbow

Solar halos have a sharp inner edge and a diffuse outer edge, and the sky around the halo is darker than rest of the sky. A tinge of red is noticed inside the halo and blue outside the halo,giving a illusion of rainbow. On the other hand, lunar halos are colorless.