why does a rainbow show a variety of colors
How is a rainbow formed? The mechanics of rainbows have been studied since ancient times. The Greek philosophers were aware of the role of reflection in forming a rainbow, and had some understanding of the role of refraction. In the 13th century, scientists produced theories on rainbow formation, and in the 17th century, Rene Descartes sketched out the conditions required to observe a rainbow. We see rainbows because of the geometry of raindrops. When the sun shines from behind us into the rain, incident rays of light enter the drop and are refracted inwards. They are reflected from the back surface of the raindrop, and refracted again as they exit the raindrop and return to our eyes. Refraction is responsible for splitting the sunlight into its component colors. Above, compare the angles from internal and double-internal reflections. There are triple- and quadruple- internal reflections as well. See up to 6 internal reflections below. Secondary rainbows are formed by double internal reflection. Light is reflected twice from the inner surface of the raindrop before leaving the raindrop. The light is concentrated between approximately 50. 4 and 53. 6, forming a secondary rainbow above the primary rainbow. The size of the raindrops does not affect the geometry of the rainbow, although very tiny drops, such as those in fog or mist, reduce the effect.
In this case, the effect of scattering overpowers the dispersive refraction effect. A "fogbow" has the arc of a rainbow, but appears as a bright white bow without spectral colors. The angle of the sun does affect the rainbow we see. Once the sun is higher than 42, the rainbow arc slips below the horizon. As the sun approaches the horizon, the size of the visible arc increases, reaching a full semicircle just before sunset. Moonbows have been observed, but as our night vision is not sensitive to color, they appear white rather than colored. If one rainbow is beautiful, a double rainbow is breathtaking. In fact, is possible for sunlight to be reflected three or more times in one raindrop, but third order rainbows cannot be seen. They form so close to the sun that its brightness overpowers them. In the laboratory, it is possible to recreate multiple rainbows formed by multiple internal reflections. A spherical flask of water simulates the raindrop. In a double rainbow, raindrops reflect the sunвs light noticeably inward from the rainbow arc, and correspondingly out of the secondary bow, so that the dark band is seen between the bows. This effect, called Alexanderвs band, was first described by the Greek philosopher Alexander of Aphrodisias in the 3rd century. The sky below the primary (lower) rainbow, and above the secondary (higher) bow, is brighter as a result.
A supernumerary rainbow forms additional bands on the inner arc of the primary rainbow, or very occasionally on the outer arc of the secondary rainbow. These bands, which usually appear in pastel colors, are caused by the interference of light waves.
I spy with my eye, seven rainbow colors in the sky. Why? It s intriguing, isn t it? Out of all the colors we can see, only seven of them are present on the rainbow. So where are the rest? No, no I m sure I m not colorblind. I can see pink, black, purple, and all the other colors around me, but I can t see those in the rainbow. Could it be possible that there are many more colors present in the rainbow, but our eyes can only distinguish those seven? PThat is precisely true. The rainbow has colors thatPrange from the ultra-violet and infrared region as well!! That s a lot of colors, but we simplyPcan t see them. Why is that? Well, let s take a walk back to our school lessons and find out. The total number of colors that our eyes can see in a rainbow is 7. The colors are always seen in the same order. These colors are (in the order that we see them from top to bottom): When we walk into a dark room, have you ever noticed that itPtakes time for our eyes to adjust? How does that happen? This actionPis due to the presence of rods and cones at the back of our eyes.
P Rods are sensitive and respond only to the presence or absence of light, whereas cones are all about colors. We have three different types of cones blue, red, and green. , When you look at a banana, your red and green cones fire up and allow you to see the yellow of the banana. Your cones activate depending on what color you see. PThe proper mixture of cones being fired up allows us to see those colors. For some colors, one cone might fire up completely, while another only fires partially. When you see the color white, for instance, all three cones will respond. Some people are colorblind because one or more of their cones don t work. P How will they see the colors of a rainbow then? Well, they ll just see a smaller set of colors or the colors will be less prominent to them. Now we know how eyes perceive colors (the cones in our eyes), but, when I look up at a rainbow, I still don t see brown, white, black, pink, and many other colors. Why is that? Well,Pthe colors we see from the rainbow are spectral colors, because these colors are also present in the visible spectrum. Notice how there s no pink or brown, or even purple? These colors don t have their own wavelength. For me to see them, they have to be mixed with colors of different wavelengths. Take pink, for example, which is only made when you mix red and blue wavelengths!
Now, back to the rainbow. Look at where the blue band is and look where the red band is. There is no overlapping of bands, so there is no pink. Next, consider purple! What is purple made of? Red and blue. As stated above, there isPno contact with each other. As for brown, which is a mix of green and red, those bands are similarly not in contact with each other in the rainbow. Now, I understand why these colors aren t up there, but what about black and white? That is the particularly interesting and brilliant part of this rainbow color mystery. White light is the reason why we see the rainbow in the first place. The colors I m seeing come from this white light. Furthermore, black is the absence of any color, and we re talking about a rainbow, so that makes sense, right? Another interesting fact is that everyone will see slightly different shades of color when we look at the rainbow. It s how our eyes look at it. Different sets of eyes means different responses to colors. I never thought that there was so much to colors. There are still plenty of colors that we can t see in a rainbow, but that doesn t mean they aren t there! These other colors are in the ultra-violet and infrared regions, which our eyes cannot naturally detect. But hey,Pwhat we can see is still pretty beautiful, right?
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