Look up at the night sky and you’ll see stars as tiny points of light. That’s what your eyes can pick up. But there’s a whole other picture hiding right in front of you, invisible to human eyes. Infrared telescopes are how we see it.
The Basics
What is infrared light?
Light comes in more types than the kind we can see. Visible light (the reds, blues, and every color in between) is just one small slice of something bigger called the electromagnetic spectrum. Infrared light is a slice right next to it. It’s invisible to us, but it’s real, and it’s everywhere.
Here’s the easiest way to think about it: infrared light is basically heat. Anything warm gives it off: your body, a cup of coffee, a car engine, a star. The warmer something is, the more infrared light it gives off. Night-vision goggles work by picking up this heat and turning it into a picture you can see. An infrared telescope does the same thing, just pointed at space instead of a backyard.
How It Works
How do infrared telescopes work?
A regular telescope, like the kind you’d look through in your backyard, collects visible light (the same light your eyes already see) and makes it brighter and bigger. An infrared telescope collects infrared light instead, using special detectors that react to heat rather than color.
A lot of the universe’s most interesting stuff is hard to see in visible light. Thick clouds of cosmic dust block visible light almost completely, much like fog blocking your headlights. Infrared light slips through that same dust far more easily, though. So an infrared telescope can see straight into places a regular telescope struggles with, like the middle of a dust cloud where new stars are being born.
There’s a catch, though. The telescope itself gives off heat, and so does everything around it, including Earth. An infrared telescope has to be kept extremely cold, or its own heat would completely drown out the faint infrared signals it’s trying to detect from space, the same way a bright flashlight makes it hard to see faint stars nearby. That’s why infrared telescopes are kept unbelievably cold, often colder than -370°F (-223°C).
Where They Live
Where are infrared telescopes located?
Some infrared telescopes sit on the ground, usually on top of tall, dry mountains where the air holds very little water vapor. Water vapor absorbs infrared light before it ever reaches the telescope. Mauna Kea in Hawaii is one popular spot for exactly this reason.
But the best place for an infrared telescope is space. It’s a vacuum, bone dry, and far from the heat radiating off any planet’s surface. The James Webb Space Telescope (JWST), the most powerful infrared telescope ever built, orbits about a million miles from Earth, far enough away to stay cold and clear.
Common Uses
What are infrared telescopes used for?
Infrared telescopes let astronomers do things visible light struggles with:
- See through dust to watch new stars and planets forming inside clouds of gas.
- Spot extremely distant galaxies. Light from the earliest galaxies has been stretched out by the universe’s expansion until it shifts into infrared. So if you want to see the oldest galaxies in the universe, infrared is the only way to do it.
- Detect cooler objects, like planets, brown dwarfs, and cold dust, that are too dim to show up well in visible light but glow steadily in infrared.
Real-World Example
A real example: the James Webb Space Telescope
JWST is the clearest real-world example of everything above. Its giant golden mirror collects infrared light, its instruments are kept extremely cold, and it sits far from Earth in a stable orbit around a point called L2. The result is a telescope that can look straight through clouds of dust to show newborn stars, or look so far back in time that it’s seeing galaxies from close to the beginning of the universe.
Below are a few real JWST images that show exactly what infrared light reveals. Each one is a place regular visible-light telescopes couldn’t see nearly as clearly.
Curious why these infrared images come out looking so colorful, since infrared light itself is invisible? That part of the story is explained in Why Are JWST Images So Colorful?
If any of these catch your eye, every image on CosmicRift is free to download, already sized for your phone, tablet, or desktop. Browse the full gallery to find more.



