Objects · Milky Way scale
Nebula
A cloud of interstellar gas and dust. Nebulae are the birthplaces of new stars and the glowing remnants of stars that have died. Five main types: emission, reflection, dark, planetary, and supernova remnant.
Notable example
The Orion Nebula (M42), just 1,344 light-years away, is a stellar nursery containing over 1,000 young stars in various stages of formation — visible to the naked eye.
Source: HubbleSite Nebulae
Nebulae — cradles and graves of stars
The word nebula (Latin: cloud) was once applied to any fuzzy, extended sky object — including what we now know to be distant galaxies. Today it refers specifically to interstellar clouds of gas (mostly hydrogen and helium) and dust within a galaxy. They are the raw material from which stars form and the enriched material returned when stars die.
The full story of how nebulae connect to the stellar life cycle is told in our what is a nebula guide and the stellar life cycle guide. Nebulae are the origin of solar systems — including ours: see how the Solar System formed.
Frequently asked questions
- The word "nebula" is Latin for cloud or mist. Its Latin plural is nebulae (pronounced "NEB-yoo-lee"). "Nebulas" is also acceptable in modern English. The word has roots in astronomy dating back to the 18th century, when astronomers used "nebula" to describe any fuzzy, extended object in the sky — including objects we now know to be galaxies, star clusters, or gas clouds. After Edwin Hubble resolved Cepheid variable stars in "spiral nebulae" in 1923 and proved they were distant galaxies, the term narrowed to its modern meaning: interstellar gas and dust clouds within a galaxy.
- Nebulae span an enormous range of sizes. Planetary nebulae — the ejected shells from dying Sun-like stars — are relatively compact, typically 1–3 light-years across (e.g., the Ring Nebula is about 1 light-year in diameter). Emission nebulae and stellar nurseries are vastly larger: the Orion Nebula spans about 24 light-years; the Carina Nebula is over 300 light-years across. Giant molecular clouds — the cold dark clouds where star formation begins — can extend over hundreds of light-years and contain enough mass to form millions of stars. The largest known, the Tarantula Nebula, spans ~1,000 light-years. In comparison, the distance to the nearest star (Proxima Centauri) is 4.24 light-years.
- A few nebulae are visible to the naked eye under dark skies. The Orion Nebula (M42) is visible as the fuzzy middle "star" in Orion's sword and is the most commonly observed nebula. The Lagoon Nebula (M8) is marginally visible in dark skies as a hazy patch in Sagittarius. The Eta Carinae Nebula is visible from the southern hemisphere. The Andromeda Galaxy was historically catalogued as a nebula ("Andromeda Nebula") and is visible to the naked eye, though we now know it is a galaxy. Through binoculars, several more nebulae become accessible; through a small telescope, dozens are observable, and with narrowband filters even light-polluted skies can reveal emission nebulae.
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