Tell Me Why?

To explain why the sky is blue we will need to take a quick look at the Sun and the atmosphere in understanding the role they play in the sky appearing blue.

Light from the sun (sunlight) is composed of seven colors (rainbow colors) of different wavelength* that blend perfectly to make the sun’s light white in appearance. This light from the Sun is called white light. The different colors in sunlight (white light) can be seen by passing sunlight through a prism (see diagram below).

When sunlight (white light) is allowed to pass through a prism, it scatters the different colors of light according to their wavelength, showing a continuous band of colors. This procedure exhibits the range (visible light spectrum) of colors - red, orange, yellow, green, blue, indigo, and violet in that order. This means that the different colors of light have different wavelengths in which red light has the longest wavelength and blue light found at the other end of the visible light spectrum has the shortest wavelength. This band of colors appear in the same pattern as the colors of a rainbow when raindrops (acting as a prism) disperse the Sun’s white light. This means you will find that white sunlight is actually composed of the colors seen in a rainbow.

The entire planet is enveloped by a blanket of air surrounding Earth. This blanket of air is called the atmosphere, which is really a gaseous layer (mixture of gas molecules) and other materials surrounding the earth. The principal constituents of the Earth’s atmosphere are nitrogen (78 %) and oxygen (21 %). The remaining atmospheric gases in the remaining 1 percent are argon (0.9 %), carbon dioxide (0.03 %), varying amounts of water vapor (in the form of vapor, droplets and ice crystals), and trace amounts of hydrogen, ozone, methane, carbon monoxide, helium, sulfur dioxide, neon, krypton, and xenon. There are also small amounts many small solid particles such as dust, soot and ashes, pollen, and salt from the oceans.

Now, when sunlight passes through the atmosphere, it collides with the gas molecules
(oxygen and nitrogen atoms). This causes the Sun’s white light to be scattered in all directions around the sky exhibiting predominatly the blue color in the visible light spectrum much more efficiently and readily than the other colors thus making the color blue becoming visible to the eye. This is due to the fact that light with the shorter wavelengths (high frequency and higher-energy e.g. blue) are scattered much more readily than those of longer wavelengths (low frequency and lower-energy e.g. red). Therefore colors of light according to their wavelength (from the longest to the shortest wavelength) are; red, orange, yellow, green, blue, indigo, and violet. The light colors of longer wavelengths pass through the Earth’s atmosphere almost unaffected (very small scattering) while much of the shorter wavelength light is absorbed by the gas molecules which then radiate in different directions. This scattering of light in all directions is called Rayleigh scattering* and the blue color of the sky is caused by this scattering of sunlight. Even though violet has a short wavelength and is scattered readily along with blue over the sky, our eyes are much more sensitive to blue light than they are to violet light and as a result of this, we see the sky as blue.
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Side Notes
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* Wavelength: It is the distance between two consecutive peaks (crests) or troughs of an electromagnetic wave. In other words, it is the horizontal distance between two successive peaks of a wave. It is usually measured in nanometers (nm). All electromagnetic radiation (radio waves, microwaves, ultraviolet light, visible light, etc.) is transmitted in waves.

* Rayleigh Scattering: Selective scattering (i.e., preferential scattering of shorter wavelengths) of light by very small particles suspended in the Earth's atmosphere, or by molecules of the air itself. This responsible for the blue of the daytime sky.

Click image to enlarge
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What is a rainbow?
Where do objects get their colors from?
From My Other Site
Why is the sky blue?
The Meaning of Colors - Color Symbolism

Labels: Colors

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Bacteria are tiny, one-celled living organisms with a tail like structure that they use to swim (flagella). They can only be seen with the aid of a microscope. They live and breed in warm, moist environments in the body and other places, where they grow quickly, causing an infection. They reproduce by a process called Binary fission. This a method of asexual reproduction (reproduction occurring without the sexual union of male and female gametes) that involves the splitting of a parent cell (one-celled organism) into two daughter cells (their offspring). Structurally they usually have an enclosed cell wall and can appear in different shapes such as rodlike, spherical and spiral. Bacterial infections can usually be treated with an antibiotic.

Viruses are smaller than bacteria and cannot be seen with a ordinary microscope (only with an electron microscope). They grow inside the body and produce toxins (poisons) that can cause infection. Viruses can not self-reproduce outside a cell of an organism (the host). They can only reproduce by using the cellular mechanism system of their host to reproduce. Structurally, virus do not have a cell wall and consist of a genetic material (DNA or RNA) that is enclosed by a protective coat of protein. This means, they may appear in several different shapes since they are not restricted by a cell wall. They can be rod-shaped, sphere-shaped or multisided. Viruses cannot be killed with antibiotics.

You can read and learn more about bacteria and virus by visiting my other site Did You Know?.

Labels: Biology, Microorganism, Science

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Thunder is caused by lightning. Lightning is a stream of electrons (electricity) flowing within or between clouds, or between a cloud and the ground (usually occurring during a thunderstorm). When a bolt of lightning shoots through the atmosphere, it rapidly heats the air up to 50,000 degrees Fahrenheit (five times the temperature of the sun) in a fraction of a second (almost instantaneously). This superheated air rapidly expands thus opening up a little hole (a partial vacuum) in the air surrounding the lightning's path, called a channel. As the superheated air quickly dissipates it's heat (cools), the air rapidly collapses (contracts), creating a tremendous shock (compress) wave. This loud cracking sound wave, is what we hear as thunder. The rumbling sound has to do with the sound echoes and reverberates as the vibrations gradually die out over distance.

The reason we see lightning before we hear thunder is because light travels faster than sound. Thunder typically can be heard 10 to 15 miles away from a thunderstorm.

Labels: Geography, Physical Geography, Science

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The reason why warm-blooded animals like dolphins and whales breath air like humans is due to the fact that it would be hard to extract enough oxygen from their water surroundings using gills. Furthermore, air has approximately 20 times more oxygen in it when compared to the same volume of water. While on the other hand, fish being a cold-blooded animal take on the temperature of their surroundings and uses less energy than that of warm blooded animals which convert the food that they eat into energy to adjust their body temperature. This reduces oxygen demands for fishes thus, gills work best with fishes.

Labels: Animals

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Stars twinkle when we observe them (from the surface of the earth) because we are viewing them through different layers of turbulent (swirling) air and temperatures in the Earth's atmosphere (the mass of air surrounding the Earth). This therefore means, the Earth's atmosphere is made up of several “layers” of moving air, each having different temperature and density.

When light from a star (traveling millions of miles) pass through these layers of the Earth’s atmosphere, it is constantly bent (refracted) by each layer of temperature and moving air several times in random directions. This random refraction distorts the image of the star slightly in brightness and position making it look as if it is moving and winking. Thus, this distorted image of the star that we are seeing in the sky causes our eyes to interpret this as a twinkling (blinking) star.

It is also important to note that in outer space stars do not twinkle because there is no atmosphere. So, strictly speaking, stars themselves do not twinkle but appear to do so through the Earth’s atmosphere.

Labels: Astronomy, Science

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