The correct option is Both A and R are true but R is NOT the correct explanation of A
Explanation
The phenomenon of twinkling is primarily caused by atmospheric refraction. As light from celestial bodies passes through the Earth's turbulent atmosphere, varying air densities cause the light path to fluctuate continuously.
- Assertion (A): Correct. Planets do not twinkle like stars. This is because planets are much closer to the Earth and appear as extended sources of light (observable disks) rather than point sources. The light coming from various points on the planet's disk undergoes refraction, but the fluctuations in intensity from different points average out. Consequently, the total amount of light entering the eye remains fairly constant, nullifying the twinkling effect.
- Reason (R): Correct. Planets are non-luminous bodies that do not emit their own light through nuclear fusion; they are visible because they reflect the light of the Sun.
Synthesis: While the Reason (R) is a factually correct statement about the nature of planets, it is not the correct explanation for the Assertion (A). The lack of twinkling is determined by the object's apparent size (extended source vs. point source) and distance from Earth, not by whether the object emits or reflects light. Even if a planet were self-luminous, it would not twinkle as long as it appeared as an extended source.
Key Takeaway: Stars twinkle because they are distant point sources susceptible to atmospheric turbulence. Planets do not twinkle because they are closer extended sources, where light variations from different points cancel each other out.