Explain why the planets do not twinkle but the stars twinkle.
The planets being closer to the Earth do not appear as point sources of light. The planet covers a small circular area in space, when viewed from Earth. So, even if light from one point in the circular disc is blocked, light from other points reaches our eyes. As the light from the planets are not completely blocked from our sight and they do not twinkle. Stars on the other hand are point sized objects and twinkle by atmospheric refraction of light.