Physics Photo of the Week

April 3, 2009

Horsehead Nebula -
Processing and Discussion by Gina Warren
First recorded in 1888 at Harvard College Observatory, the Horsehead Nebula is made of dust and non-luminous gas. It stands out as a dark, swirling cloud in the sky, and was given it’s name because of the obvious shape of a horse’s head and neck that it forms.

Also known as Barnard 33, the Horsehead Nebula is about 1600 light years away, located in the constellation of Orion, just below Alnitak, the left most star in Orion’s Belt. The Horsehead Nebula spans a distance of approximately 2.7 by 1.8 light years and is part of the optical nebula IC434. It is most visible in January.

To create this image of the Horsehead nebula, during one observation session it was photographed with green, blue, and red filters (Gina Warren, Emma Falcon, and Kendra Cole) on February 16, 2009. Twenty-three pictures were taken for each color filter.  The multiple images for each color were superimposed on top of one another, combining ("stacking") to make an image that accounted for the sum of each color: blue, red, and green. By combining the pictures that we took, the computer was able to remove cosmic rays and other forms of light interference.

Next these images were combined with a photograph of the Horsehead Nebula’s luminosity which was taken and processed in December of 2008 (Brent Figlestahler,  Melissa Hahn, Philip Hamilton, Jillian Levy, and Rebecca Moss). The resulting image shows aspects of color and luminosity. The red glow is due to hydrogen gas located behind the nebula that’s being ionized by stars. The glow is the result of a discreet emission spectrum in which electrons are emitting light as they fall from high to low levels.
The February color observation was performed by students enrolled in Earth, Light, and Sky class.  The December observation was performed by students enrolled in Contemporary Astronomy.  Gina Warren is a student enrolled in Earth, Light, and Sky.

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.

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