Color in Space

spacerings · Nov 21, 2005

Can someone please explain to me the beautiful colors that are in space photos? I am completely new to everything about space. What I'd really like explained is this series of photos http://cassfos02.ucsd.edu/public/tutorial/MW.html halfway down the page called MultiWavelength Milky Way. I tried to understand by reading the writeup on http://www.celestialimage.com/page21.html but what does Photoshop color balance mean? Those beautiful photos of the horsehead nebula, etc are they made to be colorful? I guess I'm asking is space actually in black and white and all these photos are colored to look a certain way? Thanks. -C

finaldeathh · Nov 22, 2005

I may some what know what the colors represent but I'll let the others explain it to you. But they are darn beautiful, aren't they?

jatslo · Nov 22, 2005

Primary colors are green, blue, and red; the ultraviolet and infrared spectrums are invisible to the human eye.

Saiph · Nov 22, 2005

astronomers actually get their pictures in black and white. But, we also know the wavelength and wavelength distribution of each picture. So we know which photos we took are yellow light (and how much yellow, vs how much red, etc, since it isn't pure yellow light...usually), which are blue, red, infrared etc. When people refer to color balance, it's trying to get the levels of red, blue, green, etc at the right amounts for each color. Various calibration techniques help (such as imaging an object known to be red) but often it comes down to tweaks by the person doing the work to make it look good (typically done just for publication of "cool" photos for the public). The actual research is done on the pure black and white, untouched photos. Any color used in actual data analysis is specifically defined, and often assigned on purpose. It's a common practice to make "false color" images for wavelengths of light we can't see. A common custom is for IR images, making one edge of the IR spectrum red, the other blue, and fill in the regions in between. What we see isn't really red, or blue (or whatever typically neon bright colors picked)...but with that, we can study the image easier. When you look at most images released to the public (those just meant to look cool) what's typically done is increasing the "color saturation". So the colors you see are there, just nowhere near as intense. To see what I mean, imagine painting with watercolors, very diluted, faint watercolors. That's the real thing. Then, someone comes by, and decides they want the colors to be less subtle, so most people can actually pick the color differences out. They just paint over it with non-diluted watercolors, but of the same color. You haven't changed anything, just made it more intense. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

newtonian · Nov 23, 2005

Saiph - I thought the Hubble photos in visible light were actual photos - e.g. the famous pillars of creation in Eagle nebula.

Saiph · Nov 23, 2005

:::shrugs::: they are certainly composits from black and white pictures. How "faithful" the image is, I don't know. My guess is they've only upped the color saturation so that the human eye can register it, but the actual "ratios" and thus overall color, is accurate. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

jatslo · Nov 23, 2005

Black and White pics are more interesting, I think.

harmonicaman · Nov 23, 2005

This website has a pretty good technical explanation of how the HST images are processed and colorised. I'll bet JPL and NASA use the same techniques for other space images! BTW - While tracking that site down, I ran across this scintillating item at APOD entitled: "Average Colour of the Universe". This is really exciting stuff! <img src="/images/icons/rolleyes.gif" />

spacerings · Nov 26, 2005

Harmonicaman, thank you so much for that website. It is very helpful but I need to stew on it awhile. I understand now that some colored images are using red, green and blue to show what is invisible to the eye. They are arbitrarily assigning them those colors. But I don't understand why the original filtered image is still black and white before they color it. They say that, "A colored-glass window allows only its particular color of light to pass through — it filters out the other colors of the spectrum. Hubble's filters work the same way, allowing only a specific color of light to pass through." and yet on the different pages they show things like this: http://hubblesite.org/sci.d.tech/behind_the_pictures/meaning_of_color/hubble.shtml. When you click on the red or green filter, why is the image still black? Does anyone understand why I'm confused? -C

Saiph · Nov 26, 2005

because of the way CCD's work. They are "binary", they register when a photon hits, that's it. They don't care about color, or any other property of the light. So a photon has either hit the pixel, or it hasn't. THus you get black, and white. The more photons that hit a specific pixel, the more "counts" or photon hits the pixel registers. When sent to the software, this is translated into how "white" the image is (though the number of counts is still kept for measurement purposes from the software). The only way to get a specific "color" be it red, blue, green, IR, UV, whatever, is to put filters in front of the camera, so that all other types of light are blocked. So if you take a UV picture, it'll still be black and white (the CCD tells you where the photons hit) but you'll know that the only photons that came through, are UV. You want a red picture? You put a red filter in front, assuring only red photons get through. Sure, it'll be black and white, but only the red photons were measured. So that link you posted shows how focusing only on specific ranges of light, you'll see different things. Here's a bit more caption to go along with the picture: Pick the UV setting. This B&W photo was made by counting how many UV photons hit each pixel on the CCD. More hits means more white. As you'll notice, only a small portion of the galaxy is actually lit up. Now, go to green, same deal but only with green light. This time you'll notice that more of the galaxy is lit up, but these are regions producing green light. Doing this with multiple colors can tell you all sorts of things, like where dust is (the bright IR regions) and where stars are being born (Blue and UV regions) and if they are the same regions. So, in brief: All astronomy photos are black and white. All photos are labeled with extra info telling us what light was used to make them. So we get a black and white pi <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

newtonian · Nov 27, 2005

spacerings - Remember, some of those colors are real - it depends on which photos you are referring to. For visible light photos, these two article excerpts explain: "Are Those Colors Real? People who scan the sky with a backyard telescope often feel a sense of disappointment upon first locating a famous galaxy or nebula. Where are the beautiful colors they have seen in photographs? “The colors of galaxies cannot be seen directly by the human eye, even through the largest existing telescopes,” notes astronomer and science writer Timothy Ferris, “for their light is too faint to stimulate the color receptors of the retina.” This has caused some persons to conclude that the beautiful colors seen in astronomical photos are fakes, simply added in the processing somehow. This is not the case, however. “The colors themselves are real,” writes Ferris, “and the photographs represent the best efforts of astronomers to reproduce them accurately.” In his book Galaxies, Ferris explains that the photos of faint distant objects, such as galaxies or most nebula, “are time exposures obtained by aiming a telescope at a galaxy and exposing a photographic plate for as long as several hours while starlight seeps into the photographic emulsion. During this time a driving mechanism compensates for the earth’s rotation and keeps the telescope trained on the galaxy, while the astronomer, or in some cases an automatic guiding system, makes minute corrections.” - "Awake!," 1/22/96, p. 10. "YELLOW dwarfs, red supergiants, hot blue stars, all conjure up visions of a celestial kaleidoscope. But, apart from their brightness, most of us find it hard to detect any difference between one star and another. What do the astronomers see that we don’t? Even a medium-sized telescope hardly reveals their color. Nevertheless, the color is there. As the Bible said some two thousand years ago, “star differs from star in glory” and, of course, color.—1

spacerings · Nov 30, 2005

Saiph, thank you. Now I'm starting to get there. One more question though. How can it/you whatever tell between UV photons, for example, and blue photons? I know you're using a filter but isn't a photon.... a photon?

spacerings · Nov 30, 2005

Just noticed there was a page 2 when I looked for my post. Thanks everyone. Does anyone know where I can see true color photographs? I understand they are starting with black and white and changing it to the correct colors but I'm wondering what unexagerated photos look like. Are most true to life or do most people super enhance theirs to make them extra cool?

majornature · Dec 1, 2005

Think of our sun perhaps; it appears yellow. Why? Due to Earth's atmosphere. The beautiful colors in space photos are usually pictures of star nurseries, neblaes, galaxies, and star death which give off different quantities of energy. They are colorful in its own respect. Infrared is used to see the stars in a more clear perspective since dust particles prevent us from seeing. In most cases infrared can infact distort the colors of the image or images you are seeing. <div class="Discussion_UserSignature"> We are born. We live. We experiment. We rot. We die. and the whole process starts all over again! Imagine That! <img id="6e5c6b4c-0657-47dd-9476-1fbb47938264" style="width:176px;height:247px" src="http://sitelife.space.com/ver1.0/Content/images/store/14/4/6e5c6b4c-0657-47dd-9476-1fbb47938264.Large.jpg" alt="blog post photo" width="276" height="440" /> </div>

Saiph · Dec 2, 2005

a photon is a photon...but photons differ from eachother in energy, wavelength and frequency (all these traits are related to eachother actually, as a specific wavelength gives a specific energy and frequency). So you use a material that can determine frequency, or that reacts differently to different frequencies. For instance, a prism does just that, high frequency photons are deflected more by a prism than lower frequency, this causes all the light to spread out into a rainbow. Filters are the same general idea, except they strongly react to different frequencies. They transmit (allow to pass) only specific ranges of photons. The better the filter, the tighter the range. All other frequencies are able to excite and interact with the atoms and molecules in the material, and thus get absorbed into the filter. So you have a material that passes UV photons, but blocks everything else. Or you use a combination of several materials, each blocking different ranges, but none blocking UV (same general effect). The UV filter has a composition that is unable to interact with UV frequency photons...but can interact with higher or lower freqencies. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

2709 · Dec 2, 2005

I guess I'm one of the few that still use film for astrophotography. With a good tracking mount and decent color film, you can get wonderful color out of deep space objects. There are single shot color CCD cameras as well that do a good job. Unfortunately the human eye cannot detect color in such dim objects. With a 20 minute exposure, the colors treally come out! A great website that explains some of this, and is a very easy read, is at: http://www.starizona.com/ccd/advtheorycolor.htm

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