A blue sky may be seen on a clear sunny day. But is this the genuine hue of the sky, or is this its only color? Scientists sought the answer, but the solutions were a little technical.
It included studying the nature of light, atoms, molecules, and certain oddities in the Earth's atmosphere. More so, it involved large lasers.
Why is the Sky Blue?
Why does the sky appear blue when viewed from Earth? NASA's simple answer is that it is not blue but rather scattered sunlight. The sun looks white, but it is made up of seven different colors that can be seen in the rainbow.
When white light passes through a prism, a crystal that has been uniquely formed separates into all its hues, those who have been through the Land of the Magic Windows would know that visible light is just one tiny bit of all kinds of light energy.
Like other kinds of energy traveling across the water, light energy moves in waves. They sometimes travel in short, "choppy" waves, while other types of light travel in lengthy, sluggish waves. The wavelengths of blue light are shorter than those of red light.
When sunlight enters the Earth's atmosphere, it is scattered in all directions by the gases and particles in the atmosphere. The small molecules of air in Earth's atmosphere disperse blue light in all directions, dispersing more blue than other hues because it travels in smaller, shorter waves. This is called the Rayleigh scattering, which results in the blue sky and white Sun on clear days.
But the sky lightens to a lighter blue or white as it approaches the horizon. The sunlight that reaches us from low in the sky has gone through even more air than sunlight that reaches us from above. As the sunlight traveled through this air, the air molecules scattered and rescattered the blue light in all directions several times.
The light has also been reflected and dispersed by the Earth's surface. All of this dispersion recombines the hues, resulting in more white and less blue.
Dark Skies and Shooting Stars
The night sky is dark but not completely black because of its natural illumination from the stars and the natural glow of the atmosphere, according to an article in The Conversation. On a moonless night from a place far from light pollution, hills and trees stand out against the sky.
Atoms and molecules in the atmosphere generate this light, known as airglow. In visible light, oxygen emits green and red light, hydroxyl (OH) molecules emit red light, and sodium emits a sickly yellow light. While nitrogen is significantly more prevalent in the air than sodium, it contributes little to airglow.
The various hues of airglow are due to atoms and molecules emitting certain quantities of energy (quanta) in the form of light. At high altitudes, for example, ultraviolet light may divide oxygen molecules (O2) into pairs of oxygen atoms, and when these atoms rejoin into oxygen molecules, they emit a characteristic green light.
Furthermore, bright shooting stars are visible in the night sky from the atoms and molecules and sometimes even leave visible smoke trails. These atoms and molecules are usually made up of sodium which helps astronomers observe the cosmos.
In conclusion, the sky is not just blue. Rather, it is a glow-in-the-dark night sky mix of green, yellow, and red. Its colors are from the scattered sunlight, oxygen, and sodium from shooting stars.
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