How do new telescopes work?

The James Webb Space Telescope produces incredible images by capturing infrared light. By Adi Foord

- Adi Foord

Imagine a camera so powerful it can see light from galaxies that formed more than 13 billion years ago.

That's exactly what NASA‘s James Webb Space Telescope is built to do.

Since it launched in December 2021, Webb has been orbiting more than a million miles from Earth, capturing breathtaking images of deep space. But how does it actually work? And how can it see so far? The secret lies in its powerful cameras — especially ones that don’t see light the way our eyes do.

I'm an astrophysicist who studies galaxies and supermassive black holes, and the Webb telescope is an incredible tool for observing some of the earliest galaxies and black holes in the universe.

When Webb takes a picture of a distant galaxy, astronomers like me are actually seeing what that galaxy looked like billions of years ago. The light from that galaxy has been travelling across space for the billions of years it takes to reach the telescope’s mirror. It’s like having a time machine that takes snapshots of the early universe.

By using a giant mirror to collect ancient light, Webb has been discovering new secrets about the universe.

A telescope that sees heat

Unlike regular cameras or even the Hubble Space Telescope, which take images of visible light, the James Webb Space Telescope is designed to see a kind of light that’s invisible to your eyes: infrared light.

Infrared light has longer wavelengths than visible light, which is why our eyes can't detect it. But with the right instruments, Webb can capture infrared light to study some of the earliest and most distant objects in the universe.