Physics
Planets are

luminous heavenly bodies revolving around a star
luminous heavenly bodies that do not twinkle
luminous heavenly bodies that twinkle
non-luminous heavenly bodies

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Physics
The sky appears blue because

The atmosphere scatters blue colour more than the others
It is actually blue
In white light, the blue component dominates
All colours interfere to produce blue

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Physics
Stars twinkle because

the refractive index of the different layers of the earth's atmosphere ch
the distance of the stars from the earth changes with time.
None of these
the intensity of light emitted by them changes with time.

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