Nebulae: Fine Art of the Cosmos

Within the depths of the Universe, are wonderfully complex swirling clouds of plasma, dust and cosmic rays that pervade the night sky with magnificent displays of color. In the early spring a whole multitude of these beautiful celestial objects can be seen in a single night.
They are called nebulae.

Different types of nebulae form in different ways resulting in different color effects and formations but all are beautiful.

Most nebulae form when a cloud of diffuse gas in the space between the stars, called the Interstellar Medium, collapses in under the influence of its own gravitational force. Indeed the word nebula comes from the Latin word for cloud. As the center of this cloud gets denser, massive stars may form there and their ultra violet radiation changes the surrounding gases to plasma giving the brilliant colors.

Diffuse nebulae are the most common kind. Diffuse meaning that they have no definite boundaries. Diffuse nebulae can be divided into to two groups; emission nebulae which generate significant amounts of light through ionization of the surrounding gases, or reflection nebulae. These reflect the light of neighboring stars. The Omega Nebula and The Pleiades are examples of diffuse nebulae.

Another type of nebula is planetary nebulae. The name suggests that they have some relationship to planets, but they were actually named for their resemblance to planets when they were first discovered using low-power telescopes, but with the right equipment, planetary nebulae are among the most beautiful.

Planetary nebulae form when certain stars reach the end of their life. Stars that are larger than a few times the mass of the sun generally end in a supernova which sometimes results in a supernova nebula, but the smaller stars end less dramatically. When a medium to lower mass star runs out of hydrogen to fuel itself, a loss of energy causes the star to eject its outer layers which it can no longer sustain. The star then contracts which causes it to heat up. The rise in temperature results in the star expanding again which cools the star which causes the star to eject its outer layers again. A cycle forms and the star becomes a red giant until the ejections reaches such a stage were as the star ejects its entire atmosphere into space. The result, a planetary nebula.

Among the most beautiful planetary nebulae are the Cat's Eye Nebula, the Helix Nebula and the Eskimo Nebula.

Supernova remnants are a special type of diffuse nebula that forms when a massive star explodes in a supernova. When a supernova occurs, the material of the progenitor star is sent off into the surrounding space at incredible speeds of up to 3000 km/s. The high speed of the ejected matter produces a shockwave as it sweeps up the surrounding matter causing it to heat up to the point were ionization occurs and we see the dazzling colors of a supernova remnant nebula. The Crab Nebula is one of the most notable of these.

Two of my favorite nebulae are the 'Pillars of Creation' from the Eagle Nebula, a well known diffuse emission nebula in the constellation Serpens and Eta Carinae, it is one of the largest diffuse nebulae in the sky but is not the most famous because of its location in the southern hemisphere skies. But in my opinion it is the most beautiful.

Check out the Hubble Gallery to see over 200 dazzling pictures taken by the Hubble Space Telescope at the following link to see for your self.

http://hubblesite.org/gallery/album/nebula_collection/

Sea and Sky Cosmic Wonders: Nebulae

http://www.seasky.org/cosmic/sky7a05.html

Wikipedia Nebula

http://en.wikipedia.org/wiki/Nebulae