The James Webb Space Telescope: Seeing the Universe in Infrared
Webb is the largest and most powerful space telescope ever launched. Learn why it looks in infrared, why it sits a million miles away, and what it has already shown us.
Since its launch on 25 December 2021, the James Webb Space Telescope has been sending back images that have changed how we see the early universe. Here is how it works and why it matters.
What makes Webb special
- A giant mirror. Its main mirror is 6.5 metres wide, made of 18 hexagonal segments of gold-coated beryllium. It had to be folded to fit inside the rocket and unfolded in space.
- Infrared vision. Webb sees in infrared light, which our eyes cannot detect.
- A far-off home. It orbits the Sun at a point called L2, about 1.5 million kilometres from Earth, on the side away from the Sun.
Why infrared?
Light from the very first stars and galaxies travelled for over 13 billion years across a stretching universe. The stretching, called redshift, pushed its wavelength from visible light into infrared. To see the oldest galaxies, a telescope has to see infrared. Infrared also passes through clouds of dust, letting us look inside regions where stars and planets are being born.
Why it must be cold
Warm objects glow in infrared. If Webb were warm, its own heat would drown out the faint signals it wants to see. So it carries a sunshield about the size of a tennis court, made of five layers. It keeps the telescope's instruments extremely cold, far below freezing, while the side facing the Sun gets hot.
What it is studying
The first galaxies
Webb has found galaxies that existed when the universe was only a few hundred million years old.
Star and planet formation
It looks inside dusty clouds to see baby stars and discs where planets begin.
Exoplanet atmospheres
When a distant planet passes in front of its star, Webb can analyse starlight filtered through its air to detect gases like water vapour and carbon dioxide.
Our own solar system
It has imaged planets such as Jupiter and Neptune in new detail.
How to see Webb's images yourself
NASA, the European Space Agency, and the Canadian Space Agency run Webb together, and they publish new images online for free. Many images use false colour: infrared wavelengths are mapped to visible colours so we can see the structure. They show real data, but the colours are chosen to make it understandable.
What most people miss
- Webb has found puzzles. Some early galaxies look brighter and more developed than expected, which is prompting scientists to refine their models.
- It cannot be repaired. At L2 it is too far away for astronauts to visit, so everything had to work perfectly.
- Fuel limits its life. Careful launch and manoeuvres left it with fuel for many years of operation, with estimates of more than 20 years.
