They include some of our galaxy's youngest stars. Nebulae Today, most astronomers use the term nebulae only for the clouds of dust and gases in the Milky Way and other galaxies. Both types are also called gaseous nebulae. Diffuse nebulae are the larger of the two types. Some diffuse nebulae contain enough dust and gases to form as many as 100,000 stars the size of the sun.
Planetary nebulae are ball-like clouds of dust and gases that surround certain stars.
They form when a star begins to collapse and throw off the outer layers of its atmosphere. When viewed through a small telescope, this type of nebula appears to have a flat, rounded surface like that of a planet.