Physics Photo of the Week

March 11, 2011

Orion Nebula

Description by Evelyn Breziner and Ryan Fougnier

The Orion Nebula is a diffuse nebula situated south of Orion’s Belt. It is one of the brightest nebulas in the sky, and can be observed in the night-sky in plain sight from Earth. Orion’s Nebula is one of the most photographed, examined, and investigated astronomical bodies—from it, astronomers have obtained information that has determined the formation of stars and planets from clouds made of powder and gas.  Stars are currently forming in this cloud of gas and dust.  Ever since the Hubble Space Telescope first observed the nebula in 1993, it has been an important subject of research for astronomers trying to understand how star/planet systems, like our Solar System, are formed.

This photo of the Orion Nebula was taken on the evening of March 1st by a small group from Dr. Collins’ Earth, Light, and Sky class: Kate Collins, Elan Gabel-Richards, Gabriel Sistare, Rashad Ali, James Halal, and Ryan Fougnier.
  By means of a telescope, CCD camera, and computer, this image is actually a sum of dozens of images taken over the course of a two hour observation session.  The Orion Nebula, also called M42, is located 1,344 lightyears from Earth in the constellation Orion.  Although its discovery and understanding can be credited to many astronomers over the past few hundred years, it was Charles Messier who first catalogued the nebula in detail in 1796, hence the name Messier 42, or M42. 

The Nebula has three greenish zones, in addition to some red and bluish regions with violet tints. The red tonality can be explained by the emission of hydrogen radiation. The hydrogen atoms in the cloud absorb the high energy light from ultra violet radiation from the Spectral O stars deep in the center of the nebula.  Upon absorption of the ultraviolet radiation, the hydrogen gas emits the characteristic red light. The blue-violet color is the dust in the nebula reflecting visible blue light from these same very hot Spectral O-type stars.  The cause of the green color has been a subject of much debate early in the 20th century, as astronomers had a difficult time pinpointing its exact causes. With technological advances, it was concluded that the green color was caused by the transition of an electron over an oxygen atom. This type of radiation, however, is impossible to reproduce in laboratories.  It depends upon a medium in which the excited oxygen atoms don't collide with any other atoms - characteristics that can only exist in outer space.

There will be no Physics Photo of the Week next week due to spring break at Warren Wilson College.  The next Physics Photo of the Week will be published on March 25, 2011.

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 

All photos and discussions are copyright by Donald Collins or by the person credited for the photo and/or discussion.  These photos and discussions may be used for private individual use or educational use.  Any commercial use without written permission of the photoprovider is forbidden.

Click here to see the Physics Photo of the Week Archive.

Observers are invited to submit digital photos to: