Astronomy
What Is the James Webb Space Telescope? (And What It’s Seeing)
The James Webb Space Telescope is the most powerful observatory ever launched — an infrared eye far from Earth. Here’s how it works and what it’s finding.
The James Webb Space Telescope (JWST) is the largest and most powerful space observatory ever built — a giant infrared eye parked about 1.5 million kilometers from Earth, peering further back in time than any telescope before it. Launched in December 2021, it’s a joint project of NASA, the European Space Agency (ESA) and the Canadian Space Agency (CSA), and it’s reshaping our picture of the universe.
Here’s what makes it so special.
What it is
Webb is often called the successor to Hubble, but it’s a different kind of instrument. Its headline features:
- A 6.5-meter segmented mirror made of 18 gold-coated hexagons — far larger than Hubble’s, so it gathers much more light.
- An infrared telescope. Unlike Hubble (which sees mainly visible light), Webb sees primarily in infrared, which is the key to its superpowers.
- A tennis-court-sized sunshield that keeps its instruments incredibly cold — essential for detecting faint infrared heat.
Why infrared matters
Seeing in infrared isn’t a gimmick — it’s what lets Webb do things Hubble can’t:
- Look back in time. The universe is expanding, which stretches light from the most distant, ancient galaxies into infrared wavelengths. Webb is built to catch exactly that light, so it can see galaxies as they were in the early universe.
- See through dust. Infrared passes through the clouds of gas and dust where stars and planets are born, revealing nurseries hidden from visible-light telescopes.
- Study exoplanet atmospheres. When a planet passes in front of its star, Webb can analyze the starlight filtering through its atmosphere to detect what it’s made of.
Where it sits
Webb orbits a spot called L2, a gravitationally stable point about 1.5 million km from Earth (roughly four times farther than the Moon). From there it stays lined up behind Earth relative to the Sun, keeping its sunshield pointed at the Sun and its instruments in permanent cold shadow. That distance is also why Webb — unlike Hubble — can’t be serviced by astronauts.
What it’s discovering
Since beginning science operations, Webb has delivered a steady stream of breakthroughs:
- The earliest galaxies ever observed, forming surprisingly soon after the Big Bang.
- Detailed exoplanet atmospheres, including detections of various molecules.
- Stunning images of star-forming regions, dying stars and galaxy clusters in unprecedented depth.
Webb vs. Hubble
They’re partners, not replacements. Hubble excels in visible and ultraviolet light; Webb dominates the infrared and has a much bigger mirror. Together they cover a broader span of the spectrum than either could alone.
You can’t buy a telescope like Webb, of course — but you can start exploring the same sky from your backyard. If it sparks your curiosity, see our beginner telescope guide and how to see Saturn’s rings.
FAQ
What is the James Webb Space Telescope used for?
Studying the early universe, the birth of stars and galaxies, and the atmospheres of planets around other stars — mainly using infrared light to see things older and more distant than ever before.
Is the James Webb telescope better than Hubble?
It’s more powerful in different ways: a much larger mirror and infrared vision let it see further back in time and through dust. Hubble still leads in visible and ultraviolet light, so they complement each other.
How far away is the James Webb telescope?
About 1.5 million kilometers from Earth, orbiting the L2 point — roughly four times the distance to the Moon. That’s why it can’t be repaired by astronauts the way Hubble was.
Webb’s discoveries are ongoing and announced regularly. This explainer covers the mission’s purpose and design and is reviewed periodically.