How is the sun part of a closed system?

If the sun is the system, then the space around it will be surroundings including the Planet Earth. The sun gives us the light which is made up of photons, which has 0 rest mass, so light is not a matter. So, we can say the only energy gets to transfer and hence it's a closed system.

dipole moments occur when there is a separation of charge. they can occur between two ions in an ionic bond or between atoms in a covalent bond; dipole moments arise from differences in electronegativity. the dipole moment is a measure of the polarity of the molecule.

explanation:

in inorganic chemistry -dipole moment ( μ ) is the measure of net molecular polarity, which is the magnitude of the charge q at either end of the molecular dipole times the distance r between the charges. μ = q × r.