Why is the sky blue?

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durbanville | High School Teacher | (Level 2) Educator Emeritus

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There have been many theories about light and its components. Isaac Newton in his Particle Theory of Light, discusses the fact that white light is, in fact, composed of a series of colors. The colors separate and can be seen through a prism as individual colors. Prisms, such as those used by Newton to support his theories, make light bend. Mirrors reflect light and the atmosphere or the gases present in it, make light scatter. It is this scattering of light which is responsible for the blue sky color. 

Newton and his peers argued over light and light particles or light waves and Newton's contribution cannot be overlooked. It was however, Einstein, approximately two hundred years later, in 1911, who finally resolved the issue of light and its distribution (The Quantum Theory of Light). Einstein, from a complicated formula, calculated how light scatters from molecules. Light, a form of energy, travels in electro-magnetic waves and blue has a shorter wavelength and less mass than most other colors, except violet but this is, mostly absorbed at higher altitudes and the eyes are less sensitive to violet.

However, Lord John Rayleigh, an English physicist first described the phenomena of light scattering in 1870, as proposed by John Tyndall some years earlier, and it is the so-named Rayleigh scattering which is responsible for the blue color of the sky. Short wavelengths, such as blues, are absorbed by gas molecules (oxygen and nitrogen) in the atmosphere and then radiated out in different directions which ensures that blue reaches all directions. 

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besure77 | Middle School Teacher | (Level 1) Senior Educator

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People often wonder why the sky is black at night and blue during the day. During night time, the moon and stars are the main source of  light but during the day the sun is the main source of light. The sun gives off a lot more light than the moon does. This is the first thing to keep in mind. The second thing to keep in mind is that atoms of nitrogen and oxygen in the atmosphere have an effect on the sunlight that passes through them. A physical phenomena called Rayleigh Scattering causes light to scatter when it passes through particles that have a diameter one-tenth of the color/wavelength of light. Sunlight is made of many different colors but the sky appears to be because the color blue scattered more efficiently than the other colors. This is because blue/violet wavelengths have the shortest wavelengths. This is why the sky looks blue.

When you look at the sky on a clear day, you can see the sun as a bright disk. The blueness you see everywhere else is all of the atoms in the atmosphere scattering blue light toward you. Because red light, yellow light, green light and the other colors aren't scattered nearly as well, you see the sky as blue.

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ako6777 | Middle School Teacher | (Level 1) Associate Educator

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The blue color of the sky is due to Rayleigh scattering. As light moves through the atmosphere, most of the longer wavelengths pass straight through. The sky is blue because molecules in the air scatter blue light from the sun more than they scatter red light. Little of the red, orange and yellow light is affected by the air.

"However, much of the shorter wavelength light is absorbed by the gas molecules. The absorbed blue light is then radiated in different directions. It gets scattered all around the sky. Whichever direction you look, some of this scattered blue light reaches you. Since you see the blue light from everywhere overhead, the sky looks blue."

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justaguide | College Teacher | (Level 2) Distinguished Educator

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Visible light is made of light of many wavelengths. The white light that we receive from the Sun is when passed through a prism separates into many colors. This is the result of light waves bending when they pass through the prism and shows that white light is made by many different colors.

When sun light passes through the atmosphere it is scattered by the particles of the gases that make up the atmosphere. Light waves with a shorter wavelength are scattered to a larger extent as compared to light waves with longer wavelengths. As the wavelength of light with the color blue is very short this is scattered the most by the air particles. Colors of rays with a longer wavelength like red are scattered to a smaller extent and pass directly through the atmosphere.

This is the reason why the sky is blue in color.

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llltkl | College Teacher | (Level 3) Valedictorian

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Atmosphere is composed of molecules of gases, mostly nitrogen and oxygen. When light hits them, some of it may get absorbed. Afterwards, the molecule gives off the light in a changed direction. The color that is radiated is the same color that was absorbed. This is scattering. The different colors of light are affected differently. All of the colors can be absorbed. But the higher frequencies (blues) are absorbed more often than the lower frequencies (reds). This process is called Rayleigh scattering, after Lord Rayleigh who first described it. As light moves through the atmosphere, most of the longer wavelengths pass straight through. Little of the red, orange and yellow light is affected by the air.

However, much of the shorter wavelength (blues) light is scattered by the gas molecules and spread all around the sky. Whichever direction you look, some of this scattered blue light reaches you. Hence the sky looks blue to an observer under it.

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julianej123 | Student, Grade 11 | eNotes Newbie

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In simple terms, the sky is blue because small particles scatter high-frequency light.

Out of the color spectrum, blue and violet have the smallest frequencies (the tops/crests and bottoms/troughs are much closer together, or a smaller wavelength), so they tend to "bump" into the particles in the atmosphere a lot more, or be absorbed by the particles. Once the light is absorbed by the particles the light is re-emitted in all directions. This process is called scattering. Of the colors, violet light is scattered the most, followed by blue, green, yellow, etc. Although violet light is scattered more, our eyes are more sensitive to blue, so we see a blue sky.

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sid-sarfraz | Student, Graduate | (Level 2) Salutatorian

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To know the reason behind the blue sky, first you have to understand some terms.

Wavelength is the distance between two points of waves.

Frequency is the measurement of movement of waves or how fast they are traveling measured as number of times per second.

Prism is a flat shaped triangle glass that is used to bend light.

Atmosphere is a combination of various gases that surrounds earth.

WHY THE SKY IS BLUE?

White light is emitted by the sun and we only see white light. But the fact is that the sun consists of various colors that blend together showing only white light that we can see. Hence the sun combination of various colors having different frequencies and wavelengths. 

The blue light and red light is emitted by the sun in the universe towards earth. When the sun's light enters the atmosphere, it collides with oxygen and nitrogen molecules causing red light to cross unaffected whereas blue light that has shorter wavelength scatters forming blue shade that forms blue sky, leaving the red color that affects our eyes.

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krishna-agrawala | College Teacher | (Level 3) Valedictorian

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The air in the atmosphere is basically colourless. Yet the sky appears blue doe to phenomenon known as Rayleigh scattering. The visible light consists of lights of the different colour of the rainbow. Light of different colours have different wave lengths. Red, orange and yellow lights are of longer wave length, while blue light is of shorter wavelength. As light moves through the atmosphere, most of the red, orange, and yellow lights with longer wavelength lights pass straight through without being affected by the air. However, much of the blue light with shorter wavelength is absorbed by the molecules of various gases i the air. This absorbed blue light is then radiated out from the molecules in different directions, scattering it in all directions around the sky. A person looking at the sky from any direction receives some of this scattered blue light, making the sky appear blue.

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udonbutterfly | Student, College Freshman | (Level 1) Valedictorian

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We usually see the sky as blue because hydrogen molecules in the air scattered blue light from the visible spectrum more than the red light in the visible spectrum.  This is why when we look towards the sun during sunset, we see red and orange colors because the blue light has been scattered away from the line of sight.

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lil903 | eNotes Newbie

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Sunlight reaches Earth's atmosphere and is scattered in all directions by all the gases and particles in the air. Blue light is scattered in all directions by the tiny molecules of air in Earth's atmosphere. Blue is scattered more than other colors because it travels as shorter, smaller waves. This is why we see a blue sky most of the time.

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a0w | High School Teacher | eNotes Newbie

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the reason why the sky is blue is that clear cloudless day-time sky is blue because molecules in the air scatter blue light from the sun more than they scatter red light.  When we look towards the sun at sunset, we see red and orange colours because the blue light has been scattered out and away from the line of sight.

The white light from the sun is a mixture of all colours of the rainbow.  This was demonstrated by Isaac Newton, who used a prism to separate the different colours and so form a spectrum.  The colours of light are distinguished by their different wavelengths.  The visible part of the spectrum ranges from red light with a wavelength of about 720 nm, to violet with a wavelength of about 380 nm, with orange, yellow, green, blue and indigo between.  The three different types of colour receptors in the retina of the human eye respond most strongly to red, green and blue wavelengths, giving us our colour vision.

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