What is the twinkling of stars due to?

Explain why,when the sun is overhead at noon,it appears white?

How does atmospheric refraction take place? Why do stars twinkle,but planets do not?

With the help of scattering of light,explain the reason for the difference in colours of the Sun as it appears during sunrise/sunset and noon.

$A$ person is able to see objects clearly only when these are lying at distances between $50 \text{ cm}$ and $300 \text{ cm}$ from his eye. Identify the kind of defects of vision he is suffering from. Give reason for your answer.

In myopia,what happens to the power of the eye lens?