Suddenly at around 10.45 pm tonight, got a text message from my colleague Teeba to see the moon. I got a bit surprised to get such a weird message at this time. Anyway, I went up and peeped out of the window in my room. WOW! It was a nice round halo around the moon. Today is a full moon night. I called my colleague Prasad to see this beautiful sight at night. We went out to the terrace to have a full and complete view of it.
It looks like a natural miracle. It is called as 22° halo. It is formed around the Sun or the Moon. It was a white circle around the moon. That breathtaking vision in the night sky is the result of ice crystals refracting the light of the moon. The halo rings the moon when high, thin cirrus clouds made up of millions of these crystals cover the sky. The moon’s light enters into the hexagonal-shaped ice structures and is bent before passing out another side of the crystals, causing a ring of light to appear around the moon.
Light passing through the hexagonal ice prisms is deflected twice, which produces deviation angles ranging from 22° to 50°. Lesser deviation results in a brighter halo along the inner edge of the circle, while greater deviation contributes to the weaker outer part of the halo. As no light is refracted at smaller angles than 22° the sky is darker inside the halo.
Today happens to be winter solstice. Also, there will be a total lunar eclipse visible in some parts. Tonight’s lunar eclipse of a full moon will occur on the winter solstice after 372 years, an event that hasn’t happened since 1638. We missed this opportunity at Baghdad as it is not visible from here.