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Physics & Astronomy Department

Astr110 Photography Projects, Fall 2006

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Trifid Nebula (M20), Anna Ubels

Trifid Nebula

The Trifid Nebula was discovered on June 5, 1764 by Charles Messier.  This nebula was named after its unique characteristic- there appears to be three lobes.  The distance to the Trifid Nebula is debatable, but estimates range broadly from 2,200 light years to 7,600 light years.  It is part of the Milky Way and is located in the constellation of Sagittarius.  The Trifid Nebula is estimated to have a magnitude of between 6.8 and 9.0.  It is made up of emission nebulae, reflection nebulae, and absorption nebulae.  Emission nebulae are caused by a cloud of ionized gas emitting light of various colors.  Reflection nebulae occur when light from nearby bright stars scatter off of dust particles.  An absorption nebula is a dense cloud of dust.  From our view on Earth, an absorption nebula absorbs the light from distant stars and leaves a dark, starless region.  With an age of 300,000 years, the Trifid is among the youngest of the emission nebulae.

It is easy to locate the emission nebulae, reflection nebulae and absorption nebulae in this image of the Trifid.  The red color is a result of the glowing hydrogen gas in the emission nebulae.  Although this photo most dominantly shows the emission nebulae, the reflection nebulae are present in the blue hues toward the top edge of the image.  The blue hues are due to starlight reflecting in the dust.  Thirdly, the dark bands that separate the red are caused by the absorption nebulae.  The clouds of dust are so thick that they absorb all of the light.  The angular size of the Trifid Nebula is over 14 arc minutes because it actually extends off of the top of this image. From this data, I found the linear size of the Trifid Nebula to be approximately 21.8 light years across.

References:
Perkins, Philip. "M20-Trifid Nebula-Sagittarius." Astro Cruise. http://www.astrocruise.com/m20.htm

Frommert, Hartmut. Kronbery, Christine. "Messier Object 20." Messier Catalog. http://www.seds.org/messier/m/m020.html

"Trifid Nebula." Astronomy Picture of the Day. http://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search?Trifid+Nebula

Lightner, Samuel G. "Reflection Nebulae." Fusion-Physics of a Fundamental Energy Source.http://fusedweb.pppl.gov/CPEP/Chart_Pages/5.Plasmas/Nebula/Reflection.html 

Right Ascension (J2000) 18:02:18
Declination (J2000) -23:02:00
Filters used blue(B), green(V), red(R), and clear(C)
Exposure time per filter 5x60 seconds in BVRC
Date observed

October 19, 2006