Question

why sun is hot why not Moon?

Answer 1

Since the Moon and the Earth are approximately the same distance from the Sun, they receive sunlight of the same strength. ... It is the Moon's lack of atmosphere that creates such extreme temperatures. The Moon doesn't have an atmosphere to absorb sunlight like the Earth does, and so the surface gets very hot.

Answer 2

  1.  Sun is very hot because there is a lot of burning of matter on the star Sun.  A nuclear fission chain reaction happens on the surface of Sun.  The heat produced from the nuclear reaction makes Sun red hot and some energy is emanated in the form of radiation.   This radiation carries a lot of energy.  That hits us and heats up our bodies and the atmosphere.

    There is a lot of electromagnetic radiation in the visible range.  That radiation falls in the range of color red.  Also,  the color red is not scattered much.  The other colors are scattered a lot.  So sun appears red.  Otherwise Sun could appear as a bright white circular disc.

  2.   Moon is a planet and is like Earth - in receiving light and energy from Sun.
   Moon receives radiation during the day on moon and then in the night, the energy is radiated back in to the atmosphere.  So moon remains cool.