Physics
A standing wave occurs when

Two waves overlap
The speed of the wave is zero or near zero
The amplitude of a wave exceeds its wavelength
A wave reflects upon itself

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Physics
Planets do not twinkle because

They emit light of a constant intensity
Their distance from the earth does not change with time
They are very far away from the earth resulting in decrease in intensity of light
They are nearer to earth and hence we receive a greater amount of light.

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