a large, round natural object that orbits a planet such as the Earth
The moon goes around the earth.

a mass of burning gas in space that looks like a point of light in the sky at night
Will Smith starred in a number of action movies.

fast-moving heavenly body with a solid head surrounded by a glowing cloud of gases that circles the sun
What's the best time to try to see the comet?

a white or gray thing in the sky that is made from many drops of water
Most clouds are white.