Physics
Planets are

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

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Physics
Radiocarbon is produced in the atmosphere as a result of

Action of solar radiations particularly cosmic rays on carbon dioxide present in the atmosphere.
Action of ultraviolet light from the sun on atmospheric oxygen.
Lightning discharge in atmosphere.
Collision between fast neutrons and nitrogen nuclei present in the atmosphere.

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