Why does Sun look reddish in the evening and morning: Complete Detail

You would have wondered by seeing why the sun and the surrounding sky appear red during the sunset and sunrise. The sun is on the horizon during the evening and morning, which means it is farthest from us compared to the positions of the sun at day time. All the colors of sunlight have to pass through a longer distance as compared to the distance of the sun in the daytime. All the lower wavelength colors of the light are scattered away by the gas molecules available in the atmosphere, It is only the red color which, being of high wavelength, is scattered very little, due to which only red color reaches our eyes. The color of the danger signal is always of red color because of its higher wavelength so that it could be seen from far away.

Why does the sky look blue but the sun looks red when it is on the horizon?

It looks blue because gaseous particles are very small and huge in number, these small particles scatter the smaller wavelength color blue among three primary colors red, blue, and green. Since blue is one of the three primary colors so it causes the sky looks blue. it may confuse students that when the sun is on the horizon then why does it happen that the sun’s ray appears reddish, its cause is different from the previous one. Sun is on the horizon in the evening and morning, and gaseous particles available in the atmosphere still scatter the sunlight but all the colors of the least wavelength are scattered away due to which sky looks blue because gaseous particles are huge in quantity but the sun and its rays look reddish because when the sun is at the horizon its distance from us is larger due to which larger wavelength color red reaches to our eyes rest of color faded in the way. During the daytime, the sun is nearer to us which causes all the colors scattered equally by the gaseous particles resulting in the sun and sun’s rays looking white. You can understand it through an experiment.

The experiment of showing that the Sun appears reddish in the evening and morning

If this explanation confuses you, you can understand it through the following experiment.

Place a strong source of light (S) of white light at the focus of a converging lens(Convex lens, L1). This lens refracts the light in parallel to the principal axis.

Allowing the beam of light to pass through a transparent glass tank (T) containing clear water.

Allow the beam of light to pass through a circular hole (C) created in cardboard. Obtain a sharp image of the circular hole on a screen(MN) using a second converging lens(Convex lens, L2).

Dissolve about 200 gm of sodium thiosulphate (hypo) in about 2 L of clean water taken in the tank, thereafter add 1 to 2 ml of concentrated sulphuric acid in the water. Here sulfur particles start to form within 2 to 3 minutes,we can observe it from three sides of the tank by seeing the change of white light into blue light, it happened because minute colloidal sulfur particles scatter the smaller wavelength colors of the light(i.e blue).

Now, observe the transmitted light from the fourth side facing the circular hole in MN, we see the first orange-red color and then bright crimson red color on the screen.

I think, now it would have cleared your concept clearly, this experiment makes you understand the reason for the bluish color of the sky and the reddish appearance of the sun during sunset and sunrise.

Three sides of the tank are near to our eyes,so the path of the source and our eyes is least, so we see the blue colors because smaller wavelength colors are scattered away by the particles in the same way when the sun is nearest to us, blue colors scattered less while all colors scattered equally, so the sky looks white at the noon. When we see the tank from the fourth side, in this case, the distance between the source and our eyes is the longest, thus only the higher wavelength color reaches our eyes and the colloidal solution looks reddish,it is the same case when the sun is at the horizon, only red color because of higher wavelength reaches to our eyes and least wavelength colors scattered away in the way.