Nebulae

Nebulae are clouds of gas and dust in space.

Emission Nebulae

Hot nearby stars ionize the gas, causing it to glow (usually red from hydrogen). Examples: Orion Nebula (M42), Lagoon Nebula (M8).

Reflection Nebulae

Dust scatters light from nearby stars, often appearing blue. Examples: reflection nebula around the Pleiades.

Planetary Nebulae

Shells of gas expelled by dying low-mass stars. They appear round like planets (hence the name) but have nothing to do with planets. Examples: Ring Nebula (M57), Dumbbell Nebula (M27), Helix Nebula.

Dark Nebulae

Dense clouds of dust that block light from objects behind them. They appear as dark patches against brighter backgrounds. Examples: Horsehead Nebula (B33), Coal Sack.

Supernova Remnants

Expanding shells of gas from supernova explosions. Examples: Crab Nebula (M1), Veil Nebula.