Why is the sky blue?

The atmosphere is the mixture of gas molecules and other materials surrounding the earth. It is made mostly of the gases nitrogen (78%), and oxygen (21%). Argon gas and water (in the form of vapor, droplets and ice crystals) are the next most common things. There are also small amounts of other gases, plus many small solid particles, like dust, soot and ashes, pollen, and salt from the oceans.

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. 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.

As you look closer to the horizon, the sky appears much paler in color. To reach you, the scattered blue light must pass through more air. Some of it gets scattered away again in other directions. Less blue light reaches your eyes. The color of the sky near the horizon appears paler or white.

Universal Law of Gravitation


"Every object of the universe attracts other object .the force of attraction between them is directly proportional to product of their masses and is inversely proportional to the square of distance between them.this force is along the line joining the centre of both the objects"

Mathematical form of Newtons Universal Law of Gravitation

F (gravitational force acting) = G*m1*m2/r^2

where G is the constant , m1 and m2 are masses of the two bodies and r is the distance between them. so from this we can assume that

G= F*r^2/m1*m2

Now as the mathematical form of law of gravitation remains same at any place in universe and we derive gravitational constant from that law, so it is also constant all over universe .

Henry Cavendish found the value of G which is 6.67*10^-11.