What causes a rainbow?

If you do not know what the rainbow is and what it is, you may believe the legend made by different ancient culture to explain it. Rainbow is one of the most beautiful exhibits of nature.

Rainbow is not a real "thing", it does not exist in a specific "place". This is an optical phenomenon that occurs when the sun and the atmosphere are just right - the position of the observer is just right

A rainbow needs water droplets to float in the air. That is why we saw them after the rain. The sun must be behind you, the clouds are far from the sun, and the rainbow appears

The complete rainbow is actually a perfect circle, but from the ground only a part of it can be seen. From the plane, under the right conditions, people can see the whole round rainbow

The sun shines on water drops. When light enters the droplet, the light travels more slowly through the water than in the air (because the water is darker), the light bends or refracts slightly. Then the light bounces back from the droplet and then returns in the direction of the droplet and accelerates as it flows out of the droplet

Light enters water droplets and slowly gets slower from air to thicker water. Light is reflected from the interior of the droplet and is separated into its constituent wavelengths or colors. When it leaves a droplet, it produces a rainbow

Sunlight is composed of light of various wavelengths or colors. When light enters water droplets, some wavelengths bend more than other wavelengths. Purple (the shortest wavelength of visible light) is the most curved, red (the longest wavelength of visible light) does not bend the most. Thus, when light is emitted from a water droplet, it is separated into all wavelengths. Reflecting back to your light, the sun observer from behind you, all colors of the rainbow have separated from the water droplets! Purple will be at the bottom and the top will be red

When sunlight is reflected twice on water droplets, a secondary rainbow appears. The secondary rainbow is dark, the color order is reversed, and the bottom is red. Image credit: Leonardo Weiss by Wikimedia Commons

Sometimes you can see another darker secondary rainbow on top of the main rainbow. The main rainbow is caused by reflection of water droplets. The secondary rainbow is caused by the second reflection inside the droplet. This "reflects" the light that emanates the droplet at another angle (50 ° instead of 42 ° of the red main arch). This is the reason why the secondary rainbow appears on the rainbow. The order of the color of the second rainbow is also reversed. The bottom is red and the top is purple.

Sometimes the secondary rainbow is caused by each light reflected twice in each droplet before it emerges. The second reflection causes the color reversal of the secondary rainbow. Red is at the top of the main rainbow, but at the secondary rainbow, red is at the bottom

Sometimes you can see another darker secondary rainbow on top of the main rainbow. The main rainbow is caused by reflection of water droplets. The secondary rainbow is caused by the second reflection inside the droplet. This "reflects" the light that emanates the droplet at another angle (50 ° instead of 42 ° of the red main arch). This is the reason why the secondary rainbow appears on the rainbow. The order of the color of the second rainbow is also reversed. The bottom is red and the top is purple.

Secondary rainbow is caused by double reflection of sunlight in water droplets. Technically, the secondary bow is in the center of the sun itself, but its angle is greater than 90 degrees (purple about 127 degrees, red about 130 degrees), the main rainbow appears on the same side of the sky . Its outside 10 °, viewing angle is 50-53 °. Since the "inside" of the secondary bow is "upward" for the viewer, the color seems to be inverted compared to the color of the main bow. The secondary rainbow becomes darker than the primary rainbow. This is because more light escapes from more than one reflection and the rainbow itself is distributed in a wider airspace. Each rainbow reflects white light in a colored band but is "down" for the secondary and "upper" for the secondary. The undamped sky dark area between the primary bow and the secondary bow is called Alexander's band after Alexander Aphrodisias first mentioned it.