Color Astronomy Photos
Date: Winter 2012-2013
How does those beautiful colors in astronomy photos are created? For example, the Horsehead nebula is purple. Are these real colors?
Does it happen only in nebulae? The galaxy in the link below has many red dots in it. Does it have anything to do with the colors in nebulae?
Thanks for the question. Some of the colors in astronomy are real while others are false colors. The best thing to do when you are concerned about an image is to ask how the image was acquired and how it was processed. False colors are added to help make the images easier for us to view. The eye is one of the most sophisticated viewing instruments and has the ability use color to extract meaning from a picture. A program like Adobe Photoshop or ImageJ (my favorite) are used to add false colors.
I hope this helps. Please let me know if you have any more questions.
Telescopes, like the Hubble Space Telescope, can capture the energy of a very broad range of light from distant galaxies. This means that not only can the telescopes capture visible light (the colors that we would see if we were near enough to the galaxy), but also light in the ultra-violet, infrared, and so on. More importantly, it is the energy of these lights that is captured, not the actual color. So, in a sense, what we get as raw data is whether a particular spot in the target galaxy is emitting a lot or only very little energy. That part of the galaxy might appear brighter (more energy) or dark (very little energy) - and in that sense, the picture comes in black and white, not color.
However, the telescopes have specific filters. For example, the telescope might be adjusted to capture only visible light in the blue range, or near infrared, or only ultraviolet light. Thus, each filter separates out the light from a galaxy. We can then color code this separated energy sources so that a practiced eye can extract information from an image. For example, if we color coded all ultraviolet sources as white - then someone who knows this can look at an image and know where in the galaxy there are strong ultraviolet light sources. Similarly, if we choose, we can filter red, green, and yellow bands - getting energies only in those ranges, and then by combining all three images, we get what the galaxy would look like to our eyes - much in the same way that your computer monitor combines these three different colors in order to get the whole visible light range of colors.
So, in short, depending on how the image has been processed, it might be color coded to give all sorts of information to the trained eye: actual color, specific important features, specific light sources, etc.
Greg (Roberto Gregorius)
Good question, and thanks for writing all the way from Israel. My wife and I have visited there many times. The most recent was in 2010 when I received my Doctorate from the Hebrew University.
The colors are not entirely real, although NASA makes a big effort to make them as close to natural as possible. The cameras download all the Hubble Space Telescope images as black and white, Color is added later for various reasons. One reason is to show the detail of the dispersion of chemical elements and also to focus on features that the eye might miss. In the end, however, there have never been any natural color cameras aboard Hubble Space Telescope. It was the same with the beautiful pictures Voyager sent of Jupiter; the Red Spot was red.
However, these images are black and white, so the spots left from the collision of Comet Shoemaker-Levy 9 are really black, as we saw them 20 years ago.
David H. Levy
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Update: December 2011