Physics Photo of the Week

January 21, 2011

The Trifid Nebula - Discussion by Nao Kimura

Trifid Nebula, also called Messier 20 is located about 5200 light years from the Earth, in Sagittarius. It is right North of M8. And also, on its North East direction, there is M21 open cluster. It is believed that it was discovered in 1750. It is called “Trifid” because the Nebula looks like it is divided into three parts. It is because there is a dark nebula in front of M20. M20 has different characteristic in its North part and its South part. In the North, it is a blue reflection nebula, and in the South, it is a red emission nebula. A reflection nebula is a nebula that is visible because its dark nebulas reflect other star’s lights. An emission nebula is formed by many kinds of ionization gas that radiate many different colors. It is also called HⅡ region due to the ionized hydrogen. And there are about 120 of O-type young stars and also Star clusters. Those stars radiate very intense ultraviolet radiation that ionizes the gas in the nebula.

The photo was taken by students in the Contemporary Astronomy class on August 20, 2010 by Karlyn Hunt, Casey MacMillan, Jake Gerry, Nao Kimura, and Laetitia Mead.

Physics Photo of the Week is published weekly during the academic year on Fridays by the Warren Wilson College Physics Department.  These photos feature interesting phenomena in the world around us.  Students, faculty, and others are invited to submit digital (or film) photographs for publication and explanation.  Atmospheric phenomena are especially welcome.  Please send any photos to 

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