What Are Nebulae?
Nebulae are immense clouds of gas (mostly hydrogen) and dust scattered throughout galaxies. They're among the universe's most beautiful objects — and crucially important.
Types of Nebulae
#### Emission Nebulae
Hot young stars ionize surrounding gas, causing it to glow. The Orion Nebula (visible to naked eye) is a famous example — a stellar nursery 1,344 light-years away where new stars are forming right now.
Color: Often red (hydrogen) or blue-green (oxygen)
#### Reflection Nebulae
Dust reflects light from nearby stars without emitting its own. The Pleiades star cluster is surrounded by blue reflection nebulae.
Color: Usually blue (dust scatters blue light efficiently)
#### Dark Nebulae
Dense dust blocks light from objects behind it. The Horsehead Nebula is a famous dark nebula silhouetted against a red emission nebula.
#### Planetary Nebulae
When Sun-like stars die, they shed outer layers into space. These shells glow from ultraviolet radiation from the exposed core. The Ring Nebula and Cat's Eye Nebula are stunning examples.
Not actually related to planets — the name comes from their round appearance through early telescopes.
#### Supernova Remnants
The expanding debris from stellar explosions. The Crab Nebula is the remnant of a supernova observed in 1054 CE.
Star Formation
In dense regions of nebulae, gravity pulls gas together. Protostars form and eventually ignite fusion. The Pillars of Creation (Eagle Nebula) famously show this process.
Scale
Nebulae are enormous. The Orion Nebula spans 24 light-years. The Tarantula Nebula in the Large Magellanic Cloud is 600 light-years across.
Related Reading
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