James Webb Space Telescope
What is James Webb Space Telescope?
Probes & telescopes· Launched 2021-12-25 – 5th year observing at L2. An infrared observatory at the Sun–Earth L2 point, 1.5 million km anti-sunward, peering at the first galaxies and exoplanet atmospheres.
The orbit of James Webb Space Telescope at this moment: https://nowsky.org/solar/orbit?fw=earth&sp=0.05 — replayed live, no login.
Mission timeline
Spacecraft specs
| Launch | 2021-12-25 |
|---|---|
| Location | Sun–Earth L2, 1.5M km |
| Mirror | 6.5 m gold-coated beryllium |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Frequently asked
- When did James Webb Space Telescope launch?
- 2021-12-25.
- In one line, what is James Webb Space Telescope?
- Probes & telescopes — An infrared observatory at the Sun–Earth L2 point, 1.5 million km anti-sunward, peering at the first galaxies and exoplanet atmospheres.
- What can I see of James Webb Space Telescope here?
- You can see its live position in the orbit view.
Why the mirrors are coated in gold
Webb's eighteen mirror segments are made of beryllium and coated with gold — a layer 100 nanometres thick, 48 grams of gold in all, the weight of a golf ball. Gold was chosen for its colour. Silver and aluminium reflect visible light well, but gold reflects more than 98 percent of infrared light, and almost everything Webb observes is infrared. That is why the mirrors look yellow in photographs; the colour is part of the instrument, not decoration.
Beryllium was chosen for the same reason: light, stiff and, above all, barely shrinking at −230 °C, so the mirror keeps its shape in the cold. Each segment is 1.3 m across and weighs 20 kg, and seven actuators behind it adjust its figure in nanometres so that the eighteen act as one mirror. That alignment took three months after launch, and the result was the first deep field of July 2022.
The mission in depth
The James Webb Space Telescope orbits the Sun–Earth L2 point, 1.5 million km out. Its 6.5-m mirror of 18 gilded segments launched folded like origami and deployed in space; a five-layer, tennis-court-sized sunshield chills it to −233 °C so it can see the deep past in infrared.
Infrared, because the universe expands: light from the first galaxies has been stretched into it across 13 billion years. Webb has found galaxies from within ~280 million years of the Big Bang (redshift z≈14.4, confirmed 2025) — opening the new puzzle of how the early universe grew so fast — and reads exoplanet atmospheres by spectroscopy.
Zoom out from Earth in the orbit view to spot Webb holding station at anti-sunward L2.
Unfolding JWST was an epic in itself: two weeks after launch it threaded 344 single points of failure, deploying a tennis-court sunshield and a 6.5-m mirror without one slip. Thrifty fuel use should carry it well past its 10-year design life. Its biggest bombshell so far: early galaxies that grew 'too big too soon,' handing cosmology a genuine homework problem.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.