Stars appear to be twinkling but planets do not twinkle. Why? Explain why the colour of the clear sky during day appears blue and during sunset appears red.

Explanation

Planets are much closer to the earth and are seen as exended sources, so a planet may be considered as a collection of a large number of point size light sources, although light coming from individual point sized sources flicks but the total amount of iight entering our eye from all the individual point sized sources average out to be constant thereby plancts appear equally bright and there is no twinkling of planets.
Clear sky appears blue when sunlight passes through the atmosphere having the molecules of air and other fine particles whose size is smaller then the wavelength of visible light. These molecules and perticular scatter the bluc colour nmore strongly then the other colours of spectrum. As the walength of blu: colour is more, this scaltered blue light enters our eye, so, the colour of sky appcars blue to us during day time.