Physics
The different colours of different stars are due to the variation of

Density
Radiation from them
Pressure
Temperature

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Physics
X-rays region lies between

Gamma-rays and ultraviolet region
Ultraviolet and visible region
Short radio waves and long radio waves
Visible and infra-red region

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Physics
Planets do not twinkle because

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

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