Infrared Astronomy

Infrared: Beyond the Visible
The answers to some of the universe's greatest mysteries are being beamed through the night sky in light we can't see with human eyes ... but it won't be invisible to us forever. Discover the wonder of infrared astronomy and the promise of the upcoming Webb telescope.

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Hubble's visible-light image of Jupiter contrasts with the Gemini Observatory's glowing infrared view. Infrared images of Jupiter provide information about the chemistry of the gas giant's clouds. Credit: Visible: Hubble | Infrared: Gemini Observatory
Infrared is an invisible wavelength of light beyond the red end of the visible spectrum. It's invisible to the human eye, but by detecting it we gain immensely valuable information about the workings of the universe.

We look for infrared emissions for three reasons. First is the process called "cosmological redshifting."

The expansion of the universe causes all galaxies to move away from one another, stretching the light from those galaxies as it travels across the universe. As a light wave stretches, it moves toward the red end of the spectrum — thus the name, redshifting.

If an object is extremely far away, the light stretches so much that it moves beyond the end of the visible light spectrum into the invisible infrared. So to see the farthest and earliest galaxies in the universe, we have to be able to look at the light that reaches us in the form of infrared radiation.

Second is infrared's ability to penetrate the dark clouds of dust present in the universe.

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Infrared light penetrates gas and dust clouds, allowing infrared cameras to see the stars within. The infrared view of this pillar reveals young stars, including one firing off a long jet of hot gas. Credit: Visible: Hubble | Infrared: Hubble
Everything gives off some infrared radiation, but warm objects emit large amounts. We see this effect on Earth — night-vision goggles rely on infrared vision to form an image of warm bodies, and certain snakes detect their prey with infrared-sensing organs. Dust clouds block visible light, but not infrared — so by detecting this radiation, we can see through the clouds to the warm objects within.

Third is the simple fact that some things predominantly emit infrared radiation. Not all objects glow with their own light, but even the dimmest objects give off some infrared. Older planets, dust around stars, the early stages of star formation, and clouds of dust drifting in space are all visible in infrared light.

[VISIT The Infrared Universe: See the cosmos shift between visible and infrared light]

Webb will see entirely in infrared light, bringing us pictures of a universe we've never been able to see before in such detail. But infrared astronomy brings its own set of complications.

Everything made up of atoms emits infrared light. When the atoms in an object collide or vibrate, their electrons are bumped up to a higher energy level. As those electrons return to their normal energy level, they give off radiation. Much of this radiation escapes as infrared. Warm objects, which have a great number of excited electrons, emit lots of infrared. Just like a flashlight beam being lost in the glare of the Sun, the more infrared there is all around, the harder it is to distinguish distant infrared sources.

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Spiral galaxy M101 is also called the Pinwheel Galaxy due to its distinctive shape. The infrared view brings out the galaxy's delicate dust lanes in yellow-green hues, and shows its warm dust glowing red. Credit: Visible: Hubble | Infrared: Spitzer Space Telescope
If Webb were on Earth, it would be constantly awash in the planet's own infrared haze. Astronomers avoid that by sending the telescope into space. But even that doesn't solve the problem entirely, because Webb itself — being made, after all, of atoms — will emit infrared radiation. So Webb is equipped with an open design, sunshield, and intense cooling system to keep the telescope as cold as possible, so the infrared produced by its own excited atoms doesn't overwhelm the distant emissions it's designed to detect.

Updated: May 05, 2016