HOW TO COLOR THE UNIVERSE

Although we can see thousands of stars in the night sky with just our eyes, we know there are millions of other objects out there. To see these other stars, galaxies, nebulas, and more, we need telescopes that are not only more powerful than the human eye, but that can see types of light that our vision cannot process. Each of these telescopes specializes in seeing a certain type of light and provides unique information. By combining images from multiple telescopes, we can get a big-picture understanding of objects across the cosmos. In this article, using the center of our Milky Way Galaxy, the Tarantula Nebula, and the Tycho supernova remnant as examples, we explore how different telescopes, such as NASA’s Chandra X-ray Observatory, James Webb Space Telescope, Spitzer Space Telescope, and Hubble Space Telescope, work together to produce beautiful and informative images of our Universe.


THE "INVISIBLE" UNIVERSE
Looking up at the night sky, you can see lots of black, with the stars appearing as simple white dots.But if we look deeper and with various kinds of telescopes, space and the stars that live there have a lot more to o er.
You may have heard the term visible light.This is what we call the

VISIBLE LIGHT
The small range of types of light that human eyes can see.
range of colors that humans can see.Visible light, however, is just a tiny portion of all light.If you think of a piano keyboard, visible light would be the middle C key and a few keys on either side.The rest of the keys would represent the other kinds of light out there-infrared,

INFRARED
Type of light associated with detecting heat with less energy and longer wavelengths than visible light.
X-ray, gamma ray, and ultraviolet, just to name a few.

X-RAY
Type of light with more energy and shorter wavelengths than visible light, typically associated with bone scans at the doctor.
Scientists know that objects in space give o all these kinds of light, but they are mostly invisible to the human eye.To solve this problem, astronomers build telescopes and place them on the ground or launch them into space, to detect the types of light we cannot see with our own eyes.Some types of light are absorbed by the Earth's atmosphere, so telescopes that detect those types must be put into space.Other telescopes are put into space to get a better view.

TRANSLATING LIGHT
Perhaps you are might be wondering how objects in space emit di erent types of light.Before we go any further, we should explain that light travels as a wave.Just like on the ocean, you can measure the distance between the peaks of waves of light.This is called the wavelength, and scientists use this measurement to put light

WAVELENGTH
The length di erence between two neighboring peaks of a wave or the length of one complete repetition (or cycle) of a wave.
waves into categories such as radio waves (longer wavelengths), visible light (medium wavelengths), X-rays (shorter wavelengths), for example.
Many things emit one or more kind of light, including people and non-living objects.People do not give o visible light (although we reflect visible light from the Sun and other sources), but we do give o infrared light.This is how thermal cameras, and some night vision goggles, pick up people in the dark.Just as we use di erent kinds of tools to see things here on Earth, astronomers have di erent kinds of telescopes to see a variety of phenomena out in space.
Once the data from telescopes are back on the ground, scientists can rearrange those data so our limited human senses can pick them up.They layer together various types of light using di erent colors of visible light, like red, orange, yellow, green, blue, or purple [ ].
You might be thinking, "Wait a second!Is that cheating?Did you not just say we cannot see these other kinds of light?Is this all made up?"The answer is a big NO!This is not magic or a trick: it is a translation.If you have ever visited a foreign country or spoken with someone who speaks a di erent language than you do, you have had to translate from whatever language you speak to the other language.The overall meanings do not change-just the words.The same idea is true for data.We translate data from invisible kinds of light into colors our eyes and brains can see [ ].

SEEING THE CENTER OF THE OUR GALAXY
To demonstrate, let us explore the center of our Galaxy, the Milky Way.From some parts of Earth, you can see the Milky Way stretching across a big part of the night sky.In the view shown in Figure , we are zooming in on a relatively small part of the "downtown" of our Galaxy.Buried at its center is a giant black hole, weighing about million times as much as the Sun, which astronomers have named Sagittarius A * .While we cannot see beyond the edge of the black hole itself, we can see stars, gas, dust, and more that surround it.In this figure, you can see the center of the Milky Way Galaxy in three di erent light filters (near-infrared, infrared, and X-ray).

NEAR-INFRARED
Specific type of infrared light with slightly less energy and longer wavelengths than visible light, sits in between visible and infrared light on the light spectrum.
To capture the image in Figure , of Sagittarius A * some , light-years (about , , , , , miles) away, astronomers used three di erent NASA telescopes in space.Each telescope looks at specific kinds of light and gathers important information about this region of the Galaxy.Taken together, however, they paint a more complete picture than any one telescope can get alone.
Here is what each color shows: • Yellow: This layer contains observations in near-infrared light from the Hubble Space Telescope.The Hubble data show regions where stars are being born as well as hundreds of thousands of individual stars.• Red: The Spitzer Space Telescope, which is now retired, was another space telescope that looked at infrared light.This layer has cooler kinds of infrared light than the Hubble layer, and it reveals radiation and winds from stars that create glowing dust clouds and complex structures.• Blue and violet: X-rays are not only important at your doctor's or dentist's o ce.In space, objects give o X-rays when they are very hot or energetic, which the Chandra X-ray Observatory can see.The image shows you what happens when astronomers combine X-ray data from Chandra with one of NASA's newest telescopes in space, the James Webb Space Telescope (JWST).

WHAT ELSE CAN WE SEE?
Like Spitzer and Hubble, JWST detects infrared light.However, the mirrors on JWST are much, much bigger, its instruments are much newer, and the telescope itself is located about a million miles away from Earth, where it is very cold and dark.You may have heard about the JWST or seen some of the new images it has released over the past year.
Astronomers can use the translation technique for an image of this nebula, just like they did for the center of the Galaxy.The infrared light from JWST shows us dusty parts of the Tarantula Nebula where stars are forming.In Figure , the infrared light is colored orange and brown.
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AUTHORS
KIMBERLY ARCAND Kim was working in molecular biology and public health when she was hired for NASA's Chandra X-ray Observatory at the Center for Astrophysics in .Since she always wanted to be an astronaut when she was little, this opportunity got Kim close to the cosmos but without the long-distance commute.Today, Kim uses data to tell stories about science, whether in the form of a D print of an exploded star, a sound from a black hole, or an augmented reality application of a stellar nursery.

TAYLOR KNAPP
Taylor is a first-year graduate student at Caltech and starting toward a Ph.D. in astrophysics.Her research looks at the physics behind merging black holes with the LIGO collaboration.Outside of physics, she is passionate about the history of science and loves to be outside and craft!*tknapp@caltech.edu

MEGAN WATZKE
Megan has been communicating the wonders of the cosmos for decades.After earning an undergraduate degree in astrophysics, she went onto a graduate program in science journalism.She has been the press o cer for NASA's Chandra X-ray Observatory at the Center for Astrophysics | Harvard & Smithsonian since .

TRANSLATION
Using imaging tools to correspond visible colors (red, green, purple, etc.) to invisible light values to produce a picture visible to your eyes.