Types of Nebulae
From Wikipedia, the free encyclopedia
Merriam-Webster Online defines a nebula as "...numerous clouds of gas or dust in interstellar space." FusEdWeb says that the term "nebula" was coined by astronomers to describe "fuzzy patches" in the sky that can be seen by telescope but aren't as clear as other planets and stars. (Lightner, Nebulae) In 1784, Charles Messier published his catalog of nebulae so he and his fellow comet hunters wouldn't confuse the nebulae with comets. There are several different types of nebulae- reflection nebulae, emission nebulae, planetary nebulae and supernova remnants.
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[edit] Reflection Nebulae
Reflection nebulae do just what their name implies- their dust reflects light of close stars. Therefore, reflection nebulae produce no light of their own, they are simply mirroring other astronomical bodies' light. The Pleiades M45 is a group of stars that is surrounded by a reflection nebula. The Pleiades weren't formed from the nebula, the nebula seems to have crossed into the path of the Pleiades and has been there ever since. The Pleiades can be seen with the naked eye, but one would need a telescope to see the nebula surrounding it.
[edit] Emission Nebulae
An emission nebula is a nebula made of mostly "a plasma of ionized hydrogen (HII) free electrons." (Lightner, Emission Nebulae)In layman's terms, emission nebulae are very hot because of an excess of energy which converts hydrogen into ions. Once the hydrogen is ionized, the energy levels drop and they issue light which gives the nebula its glow.
The Omega Nebula M17 has several different names- the Swan Nebula, the Horseshoe Nebula and the Lobster Nebula. Phillipe Loys de Cheseaux discovered the Omega Nebula in 1745-46. SEDS.org says that "the mass of the gas [of the Omega Nebula] has been estimated to the amount of about 800 times that of the Sun." That's a lot of gas! SEDS.org also says that the nebula extends to a distance of 40 light years. (seds.org,M17) That means that if you were to travel at the speed of light, it would take you 40 years to travel across it. That's a distance of 14,099,013,964,800,000 miles!
[edit] Planetary Nebulae
Planetary nebulae are a type of emission nebulae. A planetary nebulae occurs when a star uses all its central fuel and then emits it as "a gaseous shell." After time, the star becomes a white dwarf. Planetary nebulae are called that because early astronomers thought they were the disks of planets. (seds.org, Nebulae)
The Dumbbell Nebula is a planetary nebula. It was discovered on July 12, 1764 by Charles Messier. The star in the Dumbbell Nebula gives off so much light, a good portion of it isn't in the realm of visible light. The nebula absorbs the non-visible light and then re-emits it into the realm of visible light. Scientists are unsure as to the distance of the Dumbbell Nebula, but they're using the Hubble Space Telescope to get a more accurate idea. (sed.org, M027)
[edit] Supernova Remnants
A supernova occurs when a high mass star reaches the end of its life. It collapses in on itself and explodes. The matter that is left is called a supernova remnant. The matter then gathers gas and dust as it expands. From this comes a shock wave that ionizes the gas.
The most famous supernova remnant is the Crab Nebula M01 which was discovered by John Bevis in 1731. It was first observed in 1054 AD by Chinese astronomers. It was about 4 times as bright as Venus and was visible during the day for 23 days. The Crab Nebula has attracted a lot of interest and rightly so. This beautiful nebula isn't only lovely to look at, it's fascinating to discover how the Crab Pulsar affects the nebula itself. For more information on this relationship, visit http://www.seds.org/messier/more/m001_h2.html.
[edit] External Links
seds.ord
fusedweb.pppl.gov
NASA homepage
[edit] Works Cited
Lightner, G. Samuel. "Nebulae: Fuzzy Patches in Space." FusedWed.pppl.gov/CPEP 18 December 2000.
---. "Nebulae." FusedWed.pppl.gov/CPEP 17 November 2005.
---. "Reflection Nebulae." FusedWed.pppl.gov/CPEP 18 December 2000.
---. "Emission Nebulae." FusedWed.pppl.gov/CPEP 18 December 2000.
---. "Planetary Nebulae." FusedWed.pppl.gov/CPEP 18 December 2000.
---. "Supernova Remnants." FusedWed.pppl.gov/CPEP18 December 2000.
The SEDS Messier Catalog Webpages. By Hartmut Frommert, Christine Kronberg, Guy McArthur, and Mark Elowitz. "Messier 42." SEDS, University of Arizona Chapter, Tucson, Arizona, 1994-2006. http://www.seds.org/messier/m/m045.html. 12 April 2006.
---. "Messier 17." SEDS, University of Arizona Chapter, Tucson, Arizona, 1994-2006. http://www.seds.org/messier/m/m017.html. 9 December 1999.
---. "Messier 27." SEDS, University of Arizona Chapter, Tucson, Arizona, 1994-2006. http://www.seds.org/messier/m/m027.html. 9 December 1999.
"Messier Object 1." By Hartmut Frommert, Christine Kronberg, and Guy McArthur. SEDS, University of Arizona Chapter, Tucson, Arizona, 1994-2006. http://www.seds.org/messier/m/m001.html. 26 October 2006.
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