Why the sound of the sun does not reach the earth?
The light from the sun or the moon reaches the earth, but the sound does not. Since light is an electromagnetic wave, no inert medium is absolutely necessary for the propagation of light. Light can also travel through a vacuum. So even though most of the space between the sun or the moon and the earth is empty, the light reaches the earth through that empty space.
But, since sound is an elastic wave, sound needs a physical medium to propagate, so sound cannot propagate through the space between the Sun or the Moon and the Earth. That is why sound from the sun or moon does not reach earth.