Launched on Christmas Day in 2021, the James Webb Space Telescope is the most powerful observatory ever sent into space. Designed as the successor to the legendary Hubble Space Telescope, Webb is already transforming our view of the cosmos, peering further back in time and deeper into space than any instrument before it.
An eye that sees heat
Unlike Hubble, which sees mainly visible light, Webb observes in the infrared, the part of the spectrum we feel as heat. This is crucial because light from the most distant galaxies has been stretched by the expansion of the universe into infrared wavelengths. By detecting this faint glow, Webb can see objects that formed within a few hundred million years of the Big Bang.
A giant golden mirror
At the heart of the telescope is a 6.5 metre mirror made of 18 hexagonal segments coated in a microscopically thin layer of gold, which reflects infrared light beautifully. The mirror was so large it had to be folded up to fit inside its rocket and then unfolded in space. A tennis-court-sized sunshield keeps the instruments incredibly cold, close to minus 230 degrees Celsius.
A million miles from home
Webb does not orbit the Earth like Hubble. Instead it sits about 1.5 million kilometres away at a special gravitational balance point, keeping the Sun, Earth and Moon all on the same side so its sunshield can block their heat and light. This distance means it can never be serviced by astronauts, so everything had to work perfectly the first time.
Discoveries already pouring in
In its first years, Webb has delivered breathtaking images of distant galaxies, dying stars and planet-forming discs, and it has begun analysing the atmospheres of planets orbiting other stars in search of the ingredients for life. It promises to keep reshaping astronomy for many years to come.
