Physics Photo of the Week

April 24, 2009

Orion Nebula - in color.  Color processing and Discussion by Emma Falcon

The Orion Nebula (also known as Messier Object 42 or M42) is an emission nebula located beneath Orion’s Belt.  Emission nebulas are clouds of ionized gas which give off light of various colors. 

This specific nebula is located around 1,600 light years away from Earth.  The nebula itself is 33 light years in width and contains many young stars.  These young stars are in various early stages ranging from "not yet shining" to "possible formation of surrounding planets".  Astronomers have been watching the Orion Nebula closely in hopes to discover the secret behind the birth of stars.

On clear nights, one can often see the Orion Nebula without the use of a telescope.  If one looks at the Orion constellation, the nebula itself would be located in the center of Orion’s "sword" (a series of three stars which hang from the infamous belt).

It is a long process in order to create the color image you see here.  First, multiple black and white images had to be taken Orion Nebula (photos were taken by Brent Figlestahler Dec.  2008 and described by Molly Herold for the Jan 23 PPOW)  Later, multiple photos were taken of the nebula using green, red and blue filters (Photos courtesy of both David Penketh and Molly Herold.)  Each photo taken with a 20 second time exposure. 

Once there were enough photos through each filter (around 14 photos each) the images were then calibrated and eventually stacked depending on the color.  Stacking the images removes a lot of the "noise" or specks and blurs which play no importance within the image and results in a much clearer image.  The photos are stacked using the computer to match up the stars within the specific images to insure the whole assembly is aligned. 

Now there are four images (Black and white, red, green and blue) instead of the original 56.  When looking at the four images there is a noticeable difference within the amount of nebula visible within each.  This is because the stars give off ultraviolet waves due to their high energy.  These waves alter how the Orion nebula is photographed and observed.

Finally, the four remaining images are stacked and colored appropriately.  Using the computer, the colors are balanced properly (making sure that the colors are not bleached out and such) and the final image remains. 

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: