The rainbow

The rainbow
We can sometimes see a colorful arc in the sky. It is a rainbow. The rainbow is one of the optical phenomenon which looks very beautiful. The name of “rainbow” is also used in Japan. The name comes from a bow of rain. So, what is the rainbow? The rainbow is an arc light which has the spectrum of light from red to violet. An English chemist, Newton was the first person who mentioned that the rainbow has seven colors. He said that the original basic colors are red, yellow, green, blue, violet, orange, and indigo and between them, there are infinite variations. Therefore, in Britain, the rainbow is regarded to have seven colors. In Japan, it is also that the rainbow has seven colors. However, the number of colors in the rainbow is different in each region and age. For example, in America or France, people regard the rainbow has six colors generally. In German, five colors. In Japan, the number was also regarded as five once. The people living in Okinawa think the rainbow has two colors (red and black). There are still a lot of folk customs who believe the rainbow has two colors even now (http://ja.wikipedia.org/).
By the way, do you know how the rainbow is made? We can see light is refracted when it passes through water. Rainbows are made in the same way. When the sun light is refracted through drop of water in the air, the drop of water plays a part of a prism. Then, the light disperses and looks like a tie having many colors. It is the way rainbows are made. To observe a rainbow easily, we should water over the our eyes by hose turning our back on the sun.
We can see rainbows sometimes soon after the rains stops or in front of the water wall with a splash, or even when we water with hose with our back to the sun.
Anyway, the rainbow is very beautiful optical art.
Generally speaking, the rainbow’s shape is usually arc. But actually, there is also a straight one. Have you ever seen it? The straight rainbow is very rare, so we can hardly see it.
The straight rainbow is called “circumhorizon arc” or “circumhorizontal arc”. The first observation of the circumhorizon arc in Japan was on 6th December in 2005 at Gunma prefecture and there were inquiries to astronomical observatory if the phenomenon was an omen that would cause bad things at that time.
As well as general rainbows, this circumhorizon arc appears by the refraction of light. But this type of rainbow can appear in the particular occasion. Especially, when the light is refracted through the ice crystals in the sky whose directions are almost matched, the circumhorizon arc can appear. We see general rainbow back to the sun, but we see this circumhorizon arc in the same direction with sun. However, we cannot see this rainbow if there are clouds at a low altitude. Therefore, this straight type of rainbow is very rare. In Japan, the circumhorizon arcs are observed only dozens times a year.
If you can see it, you are very lucky.
I have never seen the circumhorizon arc, so I would like to see it sometime.
We don’t have many chances to see the rainbow, so if I see rainbow, I am very happy. I think the rainbow is the most beautiful natural phenomenon.