Nebulae- their formation and types !

Definition and history of a Nebula

The word "nebula" comes from ancient roman and European times when Latin was the principal language in the western world, and was used to define most sceintific terms. In Latin, the word nebula means "a cloud, or a mist, or a vapor". Nebulae is just the plural of nebula. Nebulae were theorized before the invention of the telescope. In ancient times, the Romans looked up at the skies, and defined all the faint, less glowing stars nebulae. The reason the Romans picked the name "nebula" was mainly for a nebula's property of being a cloud, or mist of gas. After the invention of the telescope in the 17th century, many astronomers defined many of the so-called "nebulous" objects as living, bright stars. But there were still many other nebulae that the astronomers could not define. Even today, many astronomers still can not identified many of the "nebulous" stellar bodies that they have found. These bodies are still called nebulae today.

Properties of Nebulae

Nebulae do not have any concrete properties, but their description is quite simple. Nebulae are stellar bodies that have not completely transformed into a star as well as they are also remnants of a stars. Nebulae are quite gaseous, clouds or mists of gas. They do form in many different ways, and there are many types of nebulae.

Types of Nebulae

There are five types of nebulae:

1. Reflection Nebulae
2. Emission Nebulae
3. Dark Nebulae
4. Planetary Nebulae

Reflection Nebulae

Reflection Nebulae have a very unique property. The dust and gas of this type of nebula does not emit its own light. Instead, it reflects light from nearby stars and/or galaxies. They are usually located near a really bright star in the sky.

Emission Nebulae

This type of star actually emits its own light, because of the radiation from stars within the nebulae. But the radiation emitted from the stars have a unique property. The radiation from the stars in the nebula is so strong that it can "excite" atoms that are within the nebulae, and the excited atoms will move from one energy level to the next. The result of this is the atoms emitting radiation as well.

Dark Nebulae

This type of Nebulae is different from a reflection nebulae and emission nebulae by which it absorbs some light from stars behind it. The light absorbed ends up heating the dust particles up, which results in the particles re-radiating, or emitting, some of the absorbed energy as infrared light.

Planetary Nebulae

Of all the nebulae described in this page, planetary nebulae are probably the most widely known nebula. They are formed when old stars of a size, similar to our Sun's size, have consumed most of their hydrogen fuel after billions of years. The star does not explode, but instead it ejects the gases at much lower speeds and at different times. As the star continues to cool and compress, the inner core of the star becomes very hot and explodes. The very high temperature radiation from the explosion causes the ejected gases to become radioactive. The end result is a star that glows.