Why The Sky Is Blue in a Day, Reddish In The Evening and Dark at Night?

Have you ever wondered why the sky is blue? So first of all, we should know about sun light, what is the color of sunlight? Generally, the color of sunlight is white, But white color is made up of millions of colors. There are seven important colors, which is Violet, Indigo, Blue, Green, Yellow, Orange, Red (VIBGYOR). White color is made up of these seven colors, when the sunlight enters in our atmosphere. It is scattered by all colors equally in all directions due to the presence of air molecules and dust particles in the atmosphere.

sky is blue vibgyor scatter

How are the different colors Scattered?

It depends on the size of the particles, which is present in our surroundings, such as air molecules, dust particles, and water droplet and so on. We will divide them based on the wavelength of visible light, wavelength of a wave is [400nm to 700nm].

wavelength of visible light

White light means sun light that falling on air molecules. Air molecules are scattered in different color, where Blue color is scattered the most and the Red color is scattered the least, Because blue color has shortest wavelength, while red color has longest wavelength.

That’s why the blue color is more visible than red color,  And sky seems blue. This phenomena of scattering of light are known as Tyndall Effect. now the question arises in our mind why the sky appears red in the evening and dark at night?

Why the Sky Appears Red in the Evening and Dark at Night?

Sky appears red because of sun appears red at sunrise and sunset, but why?

During sunset, the sun is near skyline. the sun has to travel the largest distance through the atmosphere to reach us. Since sunlight has to travel such a large distance in the atmosphere. At this time, most of the color get scattered, but red color is very less scattered. We already studied that red color has the longest wavelength, and blue color has the shortest. So red light is easy to reach us rather than other colors, That’s why sky appears red in the evening, and this effect is known as Rayleigh scattering.

sky red color sunset and sunrise

Why the Blue Sky looks Dark at Night?

If you are thinking it is due to the sunset, so Of Course the answer will be no. There are other reasons, So as we know that the universe is infinite. There’s no edge and homogenous. It looks same at every location, there are infinite number of stars and galaxies are distributed throughout the space.

When we looked in the sky at night, many stars shine, but the nearest stars shining more than the stars which are far away from us. So sky should be looks white as a day but its not.

Now you are thinking what about the dust particles and clouds which are present in our universe in the background. Actually, clouds heat up by absorbing the radiation of the stars and radiate some of energy they would no longer be dark. Universe is expanding, so it’s taking the light longer to reach us. Nothing can travel faster than speed of the light, we can’t see the light from galaxies.

dark black sky at night

A 13.7 billion years ago universe was so small. When the time passed, since the starting some of the stars shines in every direction. We don’t see any stars, not because of the stars light reaches to us, It is because we are getting at peak of the universe before any star has formed. Stars and galaxies moving away from us cause of universe is expanding. So we can’t see them from our naked human eye. that’s why sky looks dark at night.

Why Sky Appears White at Noon?

We can see that at noon time, light from the sun is directly overhead and travel the shorter distance. As we know that wavelength of white light is shorter, so it is easy to reach us as blue or indigo light. Red light has largest wavelength, that’s why in the evening time sun looks red. Therefore, sky appears white and little bit sky blue in noon time.

Why Sky looks Blue from Earth and Not from the Space?

As we earlier discussed that why the sky appears blue from the earth. It is just because of scattering phenomenon. But the question here is that why it’s not appeared blue while see from the space (space station). The answer is, the space has not any atmosphere. There are not any air molecules, dust particles hence it is black. There is no collision happens without air. That’s why sky looks black from the space.

earth view from space

Now, after including the different reasons of sky turning into different colors, we have come to the conclusion that the light coming from the sun in different wave length effects the particles in our sky is to turn into different colors. that’s why the sky turns into different colors according to their wavelength.

Poonam chhapola


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