Rainbows are always so beautiful… at least, in my opinion. When I see them, I feel that all my negative feelings are gone. I think many of you feel the same.
So, rainbow lovers, let’s get to know this beautiful phenomenon even more 😀
1. How can you see a rainbow?
In general, a rainbow is an optical and meteorological phenomenon. It appears as a result of light reflection in water droplets in the atmosphere. Later, it creates a spectrum of light (usually ark-shaped) in the sky. Rainbows caused by sunlight are always in the opposite direction from the sun.
We can’t approach or touch them. We can only see them. If we decide to go to the direction we think is the location of the rainbow, then you won’t find it there. You will find out that the rainbow is still far away. Even if you see someone standing next to it, the person will tell you that he/she witnesses the rainbow far from there. In conclusion, a rainbow is not a physical object. People can’t see rainbows at any angle other than at the angle of 42 degrees from the opposite direction of the sun. You can get the best view when half of the sky is still dark with raining clouds, and when you are standing at an area with clear sky in the direction of the sun. In this situation, you can witness a luminous rainbow with darkened background.
2. Just how many colors are there?
In 1672, Sir Issac Newton mentioned five colors in a rainbow: red, yellow, green, blue (now is cyan), and violet. However, later, he added orange and indigo on the list. Thus, now we have seven colors in a rainbow.
But how is red seen at the top, while violet at the bottom part of the rainbow? It’s because the spectrum of the light sent back to you from a drop at the top of the rainbow arrives in such that the red light (deviated by an angle of 42 degrees) strikes the eye while the violet light (deviated by 40 degrees) passes over your head. Thus, the top of the rainbow looks red. At the bottom of the bow, violet light arrives at your eye and red light is deviated toward the ground. Thus, the bottom part of the bow appears violet.
3. Variety of Rainbows
a. Classic Rainbow
It is the most common rainbow that people generally see. The ark-shaped rainbow extends from the ground to the other part of ground, or sometimes look vanishes in the sky.
b. Circular Rainbow
It’s actually jut a classic rainbow but it looks circular if we watch it from the air. Actually, the classic rainbows are all arcs of perfect circles, but it’s impossible for us to see it in complete circle as the ground is in the way. The center of a rainbow is where our shadows fall. If we are standing on the ground, our shadow is surely on the ground, so we just see a half of the arc. However, when we look at the rainbow from an airplane or a very high mountain, our shadows will fall above the ground level, so we may be able to watch the whole circle.
c. Secondary Rainbow / Twinned Rainbow
A primary rainbow which stands side by side with its twin is an extremely rare phenomenon. Up until now, scientists are still in debate how this happens, but there is a widely-known theory, which says that the rainbow appears due to a combination of various sizes of water drops and the air resistance. Because of air resistance, raindrops flatten as they fall. The heavier is the rain, the more likely is the flattening process. Due to different size of raindrops between two rain, a twinned rainbow may be produced.
Between the primary and secondary rainbow, there is an area which is darker than the surrounding sky. It’s called Alexander’s Band. The rainbow also has a unique characteristic. The secondary rainbow displays reversed order of colors.
d. Red Rainbow
The rainbow appears during sunrise or sunset when the sky is dominated by red and orange lights. Raindrops then reflect and retract them. As a result, the red portion of the rainbow is greatly widened. According to an optics expert Les Cowley, the inside part of the rainbow is so much brighter red than the outside because “a rainbow is not just a set of colored rings, but rather a set of colored disks. They sky inside is bright because raindrops direct light there, too.” The rainbow is best seen when the sky above it is dark and cloudy.
e. Sundog/ Mock Sun/ Phantom Sun and Moondog
This phenomenon is actually not a rainbow, but it shares similar colors with a rainbow. It can be seen in a very cold area. If ice crystals are created as a result of the cold weather, diamond dust drifts in a low level of the atmosphere. The crystals act as prisms. They bend the sunlight, let it passes through them with minimum deflection of 22 degrees. If the crystals sink in the air and are vertically aligned, the sunlight is refracted horizontally. Thus, a sundog appears. The thicker the concentration of crystals in the atmosphere, the more it can be seen clearly and perfectly.
In general, a sundog has similar colors division with a rainbow. Red is on the inside and violet on the outside. Between them are the rest of spectrum. It’s mostly seen when the sun is low and in Antarctic, where freezing temperature and snow are common. When the sun rises higher, the rays passing through the crystals are skewed from the horizontal plane. The deviation angle is increased, so the sundog will move further from the sun, though it stays at the same level with the sun.
A similar phenomenon can also happen during night. Just change the word sun with moon, then you get a moondog.
A fogbow is rarely seen since it needs a very certain portion of substances to create it. Unlike the other rainbows, a fogbow isn’t made of raindrops. It’s created by certain portion of fog.
There is a certain condition needed to support the phenomenon. It needs 0.05 mm – 0.0020 inch of water droplets to cause a very thin fog. The sunlight must be able to pass through the fog, so people can see the phenomenon at the opposite direction of the sun.
Unlike regular rainbows, a fogbow’s color is paler. Sometimes, it’s just red in the outer edge and a bit bluish on the inner edge. In some cases, it just appears white. Its outer radius is a little bit lesser than that of regular rainbows. Because of its weak color, it’s also called as a white rainbow. It’s also sometimes called sea-dogs.
The phenomenon can appear in clouds, and can be seen especially through an airplane looking downwards. This kind of fogbow is known as a cloud bow. However, if it appears at night, it’s named a lunar fogbow.
g. Waterfall Rainbow
When a stream of mist is spread by a waterfall to the air in such degree so that it mixes continuously with the atmosphere, a waterfall rainbow can be formed. The appearance is not decided based on the weather or location.
There is a waterfall rainbow known as a spray bow. It especially appears during bright days. The saturation of wind and ocean waves can form mist and moisture, which supports a spray bow to show off.
h. Fire Rainbow / Circumhorizontal Arc
It looks like a reversed rainbow though it’s actually a halo. It needs certain condition to appear. The sun has to be very high in the sky, around the elevation of 58 up to 68 degrees. There should be cirrus clouds since they will act as prisms. They should be as high as 20,000 feet and contain plate-shaped ice crystals.
It can be witnessed quite often in United States though it’s quite seldom in northern part of Europe. The visibility depends on the location and the latitude of the observer. If you want to know how you can watch it, click here.
i. Unearthly Rainbow – Titan’s Rainbow
Is there any rainbow outside our planet? Yes, there is. Scientists found one in Titan, Saturn‘s largest moon. Titan is mostly dominated by methane liquids. In addition, its clouds are humid. There, methane is just like water in our planet. It has an ocean and lakes of methane and methane rain. In conclusion, the rainbow formed on this moon is a methane rainbow. “The ingredients you need for a rainbow are sunlight and raindrops. Titan has both,” says atmospheric optics expert Les Cowley.
The rainbows on Titan is a bit different from the general ones on Earth. The spectrum is dominated by orange, influenced by Titan’s orange sky, though the colors order is still the same with the one on our planet.
However, the rainbows on this planet will be difficult to be observed. Rainbows need direct sunshine, but the gigantic satellite’s sky is very hazy. “Visible rainbows on Titan might be rare,” says Cowley. However, it is still possible to be seen using infra-red “night vision” goggles. Atmospheric scientist Bob West of NASA’s Jet Propulsion Laboratory explains: “Titan’s atmosphere is mostly clear at infrared wavelengths. That’s why the Cassini spacecraft uses an infrared camera to photograph Titan.”