Nebulae are formed primarily from interstellar gas, which consists of hydrogen, helium, and trace amounts of heavier elements.

Emission nebulae are regions of ionized gas that emit their own light due to the presence of energetic stars, often associated with the formation of new stars.

Molecular clouds are dense regions of interstellar gas and dust that serve as the primary sites for the formation of stars and nebulae.

Dark nebulae are regions of dense interstellar dust that block the light from background stars, creating dark patches in the sky.

The ionization of gas in emission nebulae is primarily caused by the intense ultraviolet radiation emitted by young, hot stars.

Planetary nebulae are formed when aging stars shed their outer layers, creating expanding shells of gas that are illuminated by the star's remaining core.

Emission nebulae typically have temperatures ranging from 10,000 to 100,000 Kelvin, which is hot enough to excite and ionize the surrounding gas.

Reflection nebulae are formed when starlight is reflected off dust particles, creating a diffuse glow around the illuminating star.

The color of an emission nebula is primarily determined by the composition of the ionized gas, with different elements emitting different colors of light.

Planetary nebulae are formed during the final stages of stellar evolution when stars shed their outer layers, creating a glowing shell of gas around the remaining core.

Emission nebulae typically have lifespans ranging from 100,000 to 1,000,000 years, depending on the mass and luminosity of the ionizing stars.

Supernova remnants are formed when the expanding shock waves from a supernova interact with the surrounding interstellar medium, creating a glowing shell of gas.

Dark nebulae are formed when dense clouds of interstellar dust absorb and scatter starlight, blocking the light from background stars.

Bipolar nebulae are characterized by their bipolar or butterfly-like shape, which is often associated with the outflow of material from a young star or protostar.