Nebula Classification

Created by Captain Alexander Gunning on Tue May 4th, 2010 @ 5:36pm

What Is a Nebula?
A nebula (from Latin: "cloud" [1]; pl. nebulae or nebul, with ligature or nebulas) is an interstellar cloud of dust, hydrogen gas, helium gas and plasma. Originally nebula was a general name for any extended astronomical object, including galaxies beyond the Milky Way (some examples of the older usage survive; for example, the Andromeda Galaxy was referred to as the Andromeda Nebula before galaxies were discovered by Edwin Hubble). Nebulae often form star-forming regions, such as in the Eagle Nebula. This nebula is depicted in one of NASA's most famous images, the "Pillars of Creation". In these regions the formations of gas, dust and other materials "clump" together to form larger masses, which attract further matter, and eventually will become big enough to form stars. The remaining materials are then believed to form planets, and other planetary system objects.

Nebula Class A - Emission Nebula

Composition Hydrogen, helium, oxygen Average Size 100 - 5,000 ly Average Temp. 10 - 20 K Lifespan 1 - 2 million years Color Red, green, blue Example Lagoon Nebula, Veil Nebula

Emission nebulas are large clouds of ionized plasma where star formation usually takes place. They are illuminated from within by groups of young stars that form in H II Regions within the nebula.

Nebula Class B H II Region

Composition Hydrogen, helium Average Size 20 - 2,000 ly Average Temp. 10,000 K Lifespan 1 - 2 million years Color Red, pink Example Eagle Nebula

An H II region is a large stellar nursery, typically located inside an emission nebula. Over the duration of its lifespan, an H II region can give birth to thousands of stars. Gravimetric forces by the larger stars will eventually disperse the nebula and leave behind a star cluster similar to the Pleiades.

Nebula Class C Bok Globule

Composition Hydrogen, helium, carbon Average Size 1 ly Average Temp. 3 K Lifespan 1 - 2 million years Color Black Example NGC 281, NGC 1999, BHR 71

An H II region is a large stellar nursery, typically located inside an emission nebula. Over the duration of its lifespan, an H II region can give birth to thousands of stars. Gravimetric forces by the larger stars will eventually disperse the nebula and leave behind a star cluster similar to the Pleiades.

Nebula Class D Reflection Nebula

Composition Hydrogen, carbon, iron, nickel Average Size 100 ly Average Temp. 25,000 K Lifespan 10 million - 10 billion years Color Blue, purple Example Trifid Nebula, Witchhead Nebula

Reflection nebulas are large clouds of dust that reflect light from nearby stars. The nearby stars are not usually hot enough to cause ionization, but are bright enough to make the dust visible. Star formation can occur within a reflection nebula.

Nebula Class E Planetary Nebula

Composition Carbon,oxygen,nitrogen,calcium Average Size 1 ly Average Temp. 10,000 K Lifespan 10,000 years Color Orange, green, blue Example Ring Nebula, Hourglass Nebula

Despite the name, planetary nebulas have nothing to do with planets. They are, in fact, the final stage of life for most stars, developing when a star is no longer able to sustain nuclear fusion. As the star's core contracts, it ejects ionized gases into space, creating a planetary nebula. This plays a crucial role in the evolution of the galaxy, for the process returns material to the interstellar medium.

Nebula Class F Dark Nebula

Composition Hydrogen Average Size 200 ly Average Temp. 7 K Lifespan 1 - 2 million years Color Black Example Coalsack Nebula, Snake Nebula

Dark nebulas are a type of large molecular cloud. The cloud cores are completely invisible to the naked eye, and are be undetectable aside from microwave emissions from the molecules within. Dark nebulas have strong magnetic fields that create considerable gravimetric forces in and around the nebula. Stars and astrophysical masers can form deep inside dark nebulas.

Nebula Class G Supernova Remnant

Composition Ionized hydrogen, oxygen Average Size 3 ly Average Temp. 10,000,000 K Lifespan 1,000,000 years Color Varies; typically orange, blue Example Tycho's Remnant,1987A

When a massive star reaches the end of its life, it explodes in an immensely powerful supernova. This event blows the entire star apart, leaving in its wake a remnant nebula that expands into the interstellar medium.

Nebula Class H Nova Remnant

Composition Ionized hydrogen, oxygen Average Size .5 ly Average Temp. 5,000 K Lifespan 300 years Color Varies; typically blue, orange Example RR Pictoris

Nova remnants are similar to supernova remnants, only much smaller on all levels. They are also much more common.

Nebula Class I Solar Nebula

Composition Hydrogen, helium, oxygen Average Size 100 AU Average Temp. 150 K Lifespan 2,000,000 years Color Yellow, orange Example Panak

While most stars form within emission nebulas, there are exceptions to the rule. When a young star forms elsewhere, gravimetric forces gradually attract a disk of dust and gas that flatten to form a new star system that includes planets and asteroids.

Nebula Class J Wolf-Rayet Nebula

Composition Helium, carbon, oxygen Average Size .5 ly Average Temp. 25,000 - 50,000 K Lifespan 1 - 2 million years Color Blue Example NGC 6888, NGC 3199

A Wolf-Rayet nebula forms when strong stellar winds cause a Class O star to rapidly lose its mass. The dispersed mass forms a nebulous halo around the star.

Nebula Class K Inversion Nebula

Composition Ionized plasma strings Average Size 200 AU Average Temp. 10,000 K Lifespan 5 - 10 years Color Pink Example Marayna's Nebula

Inversion nebulas are rare, highly unstable nebulas created by plasma strings. They typically burn out after a few years.