A supernova remnant is the expanding shell of gas and dust ejected by a star during a supernova explosion.

Emission nebulae are excited by ultraviolet radiation from nearby hot stars, causing the atoms and molecules in the nebula to emit light.

Emission nebulae contain ionized hydrogen gas, which emits light when excited by ultraviolet radiation.

Dark nebulae are regions of interstellar gas and dust that are so dense that they block out the light from stars and other celestial objects.

Planetary nebulae are formed when a star sheds its outer layers at the end of its life, creating a glowing shell of gas and dust.

Reflection nebulae reflect starlight due to the presence of small dust particles that scatter the light in all directions.

Emission nebulae are often associated with the formation of new stars, as they provide the raw material for star formation.

Molecular clouds are nebulae composed primarily of molecular hydrogen gas, which is the coldest and densest form of interstellar gas.

Planetary nebulae are known for their intricate and delicate structures, often resembling flowers or butterflies, which are created by the interaction of the expanding gas and dust with the stellar wind from the central star.

The heliosphere is a bubble-shaped region of space created by the interaction of the solar wind with the interstellar medium.

Radio nebulae are characterized by their ability to emit radio waves, which are produced by the interaction of high-energy particles with magnetic fields.

Supernova remnants are formed by the remnants of a supernova explosion, and they often contain a variety of elements that have been synthesized during the explosion.

Dark nebulae are known for their ability to absorb and scatter light, making them appear dark against the background sky.

Wind nebulae are formed by the interaction of a stellar wind with the interstellar medium, and they often have a comet-like appearance.

Infrared nebulae are characterized by their ability to emit infrared radiation, which is produced by the heating of dust particles by starlight.