Physics
Planets are

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

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Physics
It is dangerous to observe Solar eclipse with naked eyes because

All radiations from sun initiate chemical reactions in eyes
Ultraviolet radiations from Sun burn our retina
Infrared radiations from sun burn our retina
Cosmic rays reach eyes more during the eclipse

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