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Iconic Hubble images are actually black-and-white
Any iconic image of the universe you can think of was probably taken by the Hubble Space Telescope. Take the Eagle Nebula, for example, which is shown below. What you might not realize is that this spectacular, colored photograph was originally black and white. Now, the experts at NASA have shown how they, quite literally, color the universe by working from Hubble's achromatic world.
(National Geographic on YouTube (Original image accredited to: NASA, ESA, STScI, J. Hester and P. Scowen))
Stars, like our sun, start off as nothing more than tiny balls of gas and dust that then grow big and bright within dense clouds, like inside of the Eagle Nebula, which Hubble first photographed in 1995.
The photo itself was so spectacular that NASA gave it a name referring to the stellar formation hidden within: "Pillars of Creation." But this picture didn't start off as the colorful masterpiece you see above.
Originally, Hubble snaps multiple pictures of an object in different wavelengths that show up in arresting black and white, shown below. Experts then use colored filters to tease out the final product.
(National Geographic on YouTube)
How do you go from black and white to awe-inspiring color? That's where Photoshop comes in.
Zolt Levay, of the Imaging Team at the Space Telescope Science Institute that runs Hubble, showed National Geographic how he transforms these images.
Your browser does not support the video tag. National Geographic on YouTube
The red, green, and blue filters he uses (shown on the right in the GIF), represent different elements that are part of the nebula's chemical make-up. Here, red indicates the presence of sulfur, green is for oxygen, and blue represents hydrogen — the most abundant element in the universe.
The reason Levay uses the colors he does is because each element glows at different wavelengths, which scientists determine in labs here on Earth.
If you take a tube of pure hydrogen gas, for example, and excite the atoms so they release light, the tube will glow blue because that's the color in which hydrogen radiates most strongly. Below is an example of the colors certain gases, including Helium and Neon, release:
(Alchemist-hp on Wikipedia)
After layering one filtered image atop the other, the final colorful image gives astronomers an idea of where and how much of each of these elements are in the nebula.
"It's pure science that's driving the colors," Levay explains in a video by National Geographic. Each of the three colors that Levay uses in his example represents elements that exist both here on Earth and in space.
For more examples of transformed Hubble images check out Hubble's Toolbox.
Watch the full video from National Geographic below:
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