Why is the sky blue? Detailed explanation.

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Main topic: Science
Other topics: Physics
Short answer:
  • When sunlight penetrates the earth's atmosphere, it gets dispersed in all directions by gases and particles that make up the atmosphere. Most of the time, we see a blue sky because blue light travels in much shorter and more compact waves.
Blue sky with wisps of cloud on a clear summer morning

Light always travels in a straight line until something enters its path and causes it to behave in one of the following ways; bend it like a prism, reflect it like a mirror, or disperse it in all directions (like molecules of gases in the atmosphere)[1][2]. The blue color is seen in the sky throughout the day when no clouds are present because particles in the air scatter blue light from the Sun more than they scatter red light. When we turn our attention to the direction of the Sun during the twilight hours, the colors red and orange come into view. This is because the blue light is dispersed away from our line of sight[3][4].

All the rainbow colors are combined to create the white light that comes from the Sun. Isaac Newton was the one who first showed this. He used a prism to separate the various colors and generate a spectrum. The spectrum of colors results from the range of wavelengths that make up light. The visible portion of the electromagnetic spectrum extends from a red light, which has a wavelength of about 720 nanometers (nm), all the way down to violet light, which has a wavelength of approximately 380 nanometers (nm), with yellow, orange, blue, green, and indigo light in between. Our ability to see colors comes from the three distinct kinds of color receptors in the human eye's retina. These receptors react strongly to red, green, and blue light wavelengths[5].

Tyndall Effect (Rayleigh scattering effect) is a phenomenon that provides an accurate explanation of the color of the sky[edit]

Rayleigh sunlight scattering

In 1859, John Tyndall made some of the first strides in providing an accurate explanation of the color of the sky. He discovered that the shorter blue wavelengths are scattered more powerfully than the red when light travels through a transparent fluid containing the microscopic suspended particles. It's because the blue wavelengths are shorter. It is possible to show this by passing a beam of white light through a water container with milk or soap in the mixture. The blue light may see the beam it scatters from the side, but when viewed straight from the end, the light is reddish since it needs to go through the tank first[6].

The Tyndall effect is the most accurate name for this phenomenon; nevertheless, physicists usually refer to it as the Rayleigh scattering effect, named after Lord Rayleigh, who conducted a more in-depth study of the phenomenon a few years later. He demonstrated that for particles of sufficiently tiny size, the quantity of light that is scattered is inversely proportional to the fourth power of the wavelength. Therefore, blue light is dispersed ten times more than red light[7].

Breaking the myth: The blue color of the sky is not due to the presence of dust particles and droplets of water vapor that float in the atmosphere[edit]

Tyndall and Rayleigh hypothesized that the blue color of the sky must be caused by tiny dust particles and droplets of water vapor floating in the atmosphere. Even in modern times, many mistakenly assert this is the situation. Later, scientists concluded that if this were correct, there should be a high difference in the color of the sky with moisture or clouds conditions than what was observed; therefore, they correctly hypothesized that the molecules of oxygen and nitrogen in the air are sufficient to account for the scattered light[8].

The sky is not violet despite the shortest wavelength because it excites the red color receptors of the eyes in addition to the blue cones[edit]

If shorter wavelengths are scattered more strongly than longer wavelengths, then it is a mystery as to why the sky does not seem violet, which is the color that has the visible wavelength that is the shortest. The spectrum of light emitted by the Sun is inconsistent throughout all wavelengths. In addition, the high atmosphere absorbs some of the light, reducing the amount of violet in the light. Human eyes are far less receptive to violet. That is a portion of the answer, but the presence of a rainbow demonstrates that there is still a significant quantity of visible light with indigo and violet colors beyond the blue. How our eyes take in and process information is the next piece of the equation to be solved. In our retina, we have three different kinds of color receptors, sometimes known as cones. They get their names, red, blue, and green, from the wavelengths of light to which they react most strongly: red, blue, and green. Our visual system creates the colors we perceive by stimulating various cones, rods, and cone groups in varying degrees.

When we gaze up at the sky, the red cones in our eyes react to the minute amount of dispersed red light, but they also respond, although to a lesser extent, to wavelengths of orange and yellow light. Yellow, as well as the green and green-blue wavelengths, dispersed more intensely, are what the green cones react to. The cones that respond to blue are triggered by colors close to blue wavelengths that significantly scatter light. If indigo and violet weren't part of the spectrum, the sky would seem more cyan than blue, with a hint of green. However, the wavelengths of indigo and violet that are dispersed most powerfully excite the red cones somewhat in addition to the blue cones. This is why specific colors seem blue with an extra reddish tint. The light from the sky stimulates the blue cones to a greater extent than the red and green cones, which results in an effect that is about equivalent. The color of the sky may be attributed to this particular combination. Our eyes may be calibrated to view the sky as a color for a reason other than sheer coincidence. Our capacity to differentiate between the colors seen in nature is likely an adaptation that helped us survive by allowing us to better fit into our surroundings as we developed[9].

Sunset over water is mainly red due to salt particles in the air acting as powerful Tyndall scatterers[edit]

Red sunset of lake Siutghiol (AP4K1102 1) (20746999743)

Since the light from the Sun has traveled such a great distance across the air, the sky at sunset will seem yellow when the air is clean. This is because part of the blue light was already scattered throughout this process. Suppose more tiny particles are in the air, whether naturally occurring or artificial. In that case, the sunset will be more crimson because of salt particles in the air acting as powerful Tyndall scatterers. Sunsets that occur over bodies of water may sometimes have an orange hue. Both the light emanating straight from the Sun and the sky surrounding it seems to have taken on a crimson tint. This is because the light is dispersed quite efficiently via small angles[10].


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  4. "Why Is the Sky Blue? | NOAA SciJinks – All About Weather". scijinks.gov. Retrieved 2022-11-12.
  5. "Why Is the Sky Blue? | Wonderopolis". www.wonderopolis.org. Retrieved 2022-11-12.
  6. "Why Is the Sky Blue?". HowStuffWorks. 2008-10-07. Retrieved 2022-11-12.
  7. "Why is the sky blue?". www.rmg.co.uk. Retrieved 2022-11-12.
  8. "Why is the sky blue?". math.ucr.edu. Retrieved 2022-11-12.
  9. "Why is the sky blue?". math.ucr.edu. Retrieved 2022-11-12.
  10. published, Andrew May Contributions from Scott Dutfield (2022-08-25). "Why is the sky blue?". Space.com. Retrieved 2022-11-12.