What is a Nebula? Part 1, Different Kinds of Nebulae

What is a nebula? A nebula is a conglomeration of gases (hydrogen, helium and other ionized gases) and dust in outer space - a cloud. It is sometimes the remains of dead stars. It is also the location of many stellar nurseries, such as the Eagle Nebula and its “Pillars of Creation” where stars are constantly being formed. In these nebulae, components clump together to form stars.

Note: Nebula can be pluralized as nebulae or nebulas. It is acceptable either way.

Different groups of people group or classify nebulae into different categories. Here we will look at the different classifications that are used.

Nebulae come in various shapes and sizes. The word “nebula” is derived from the Latin word meaning "cloud". Depending upon their characteristics, astronomers divide nebula into various different classifications:

• Absorption Nebulae
• Dark Nebulae
• Diffuse Nebulae
• Emission Nebulae
• Planetary Nebulae
• Protoplanetary Nebula
• Reflection Nebulae
• H II Regions
• Supernova Remnant

Absorption nebulae, also referred to as dark nebulae, are clouds of dusts and gases that are so thick that the totally block light from the areas of space behind it. Light is not able to pass through an absorption nebula. These nebulae are hard too spot in a dark area of space because these dark clouds can only be seen when silhouetted by much brighter areas of space.

Diffuse nebula are nebula which have no defining shape or boundary. Examples of a Diffuse Nebula is the Trifid Nebula, Carina Nebula and Tarantula Nebula.

An emission nebula is a cloud of hot glowing dusts and gases. These nebulas cannot produce their own light and rely upon nearby stars from which they absorb heat. These nebulae reach extremely high temperatures which causing them to glow. These nebulae are generally located near newly forming stars.

A planetary nebula is produced when a dead or dying star ejects its outside layers when it has burned-out. These ejected layers of gas move out into space and form a spherical-shaped nebula. The remains of the star from which the nebula was formed can usually be seen glowing in the center of the nebula. Examples of planetary nebulae are the Helix Nebula, the Egg Nebula, or the Butterfly Nebula.

Planetary Nebula are created as a final phase of a low-mass star’s existence. The Earth’s sun is an example of a low-mass star. When the low-mass star has lost enough material, its temperature rises causing ultraviolet radiation, which ionizes the materials it has thrown off.

A Protoplanetary nebula is formed from the rapid creation of a star via stellar evolution. An example of a protoplanetary nebula is the Egg Nebula.

A reflection nebula does not have the ability to create its own light, but relies on the light of nearby stars to reflect off of its cloud of dusts and gases. Reflection nebulas are the brightest where new stars are being born (stellar nurseries). Sometimes the gas and dust is so thick that the new stars are invisible.

H II region nebulae, such as the Pelican Nebula and the Rosette Nebula, are created when stars collapse upon themselves. H II region nebulae include reflection nebula, bright nebula, and diffuse nebula. The amount of gas available in the original cloud determines the size of the nebula. Stellar nurseries, where new stars are formed, are found in these nebula.

Supernova remnant nebulas, such as the Crab Nebula, are created by the explosion of a supernova. The explosion ejects material which is then ionized by the energy while a mass of compressed material remains.

Dark nebula, also referred to as absorption nebula, are thick clouds of dust and gas that have the ability to totally block light from passing through it. The Eagle Nebula and the Carina Nebula are examples of a dark nebula.

To see a photograph of and to learn more about each nebula, listed in alphabetical order below, click on the hyper-links. You will be taken to a location within this article, or off-site to a location within another site.

• Angel Nebula - part of the UNP (Unexplored Nebulae Project) whose goal is to discover, catalog and image unexplored nebulae of the Milky Way Galaxy.
• Ant Nebula
• Barnard's Loop Nebula
• Boomerang Nebula
• Bubble Nebula
• Bug Nebula
• Butterfly Nebula
• Carina Nebula
• Cat’s Eye Nebula
• Cat’s Paw Nebula
• Cave Nebula
• Christmas Tree Nebula
• Cirrus Nebula
• Cocoon Nebula
• Cone Nebula
• Crab Nebula
• Crescent Nebula
• Cygnus Loop Nebula
• Doradus Nebula
• Dumbbell Nebula
• Eagle Nebula
• Egg Nebula
• Elephant's Trunk Nebula
• Eskimo Nebula

• Eta Carina Nebula
  

• Eye of God
• Flame Nebula
• Fox Fur Nebula
• God's Eye Nebula

• Great Nebula in Carina

• Gum Nebula
• Heart Nebula
• Helix Nebula
• Horsehead Nebula
• Hourglass Nebula
• Keyhole Nebula
• Kronberger 61 Nebula
  
• Lagoon Nebula
• Little Ghost Nebula
• Necklace Nebula
• North America Nebula
• Omega Nebula
• Orion Nebula
• Pelican Nebula
• Pencil Nebula
• Red Rectangular Nebula
• Red Square Nebula
• Ring Nebula
• Rosette Nebula
• Seagull Nebula
• Spirograph Nebula
• Stingray Nebula
• Swan Nebula
• Tarantula Nebula
• Triangulum Nebula
• Trifid Nebula
• V838 Monocerotis
• Veil Nebula
• Wizard Nebula

The videos below have been provided for your enjoyment.

This completes the overview of all nebulae. To view individual nebula and learn more about them, click on the alphabetical groupings below, or choose from the individual listings above.

To continue reading in the series, click on the link below for: What is a Nebula? Part 2, Common Names for Nebulae A-C and Their Information.

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Copyright © 2011 Cindy Murdoch

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For a comprehensive slide show of nebulae photos taken by Hubble, click here.

These are the articles that complete this series concerning nebula.

• What is a Nebula? Part 2, Common Names for Nebulae A-C and Their Information
• What is a Nebula? Part 3, Common Names for Nebulae D-G and Their Information
• What is a Nebula? Part 4, Common Names for Nebulae H-O and Their Information
• What is a Nebula? Part 5, Common Names for Nebulae P-Z and Their Information

• StarryWonders Astrophotography
• HubbleSite - Out of the ordinary...out of this world.
• NASA - Home