James Webb Space Telescope

The James Webb Space Telescope is an international mission led by NASA with ESA and the Canadian Space Agency. Its development required a large infrared observatory to survive launch while folded inside an Ariane 5 fairing, then deploy its mirror, sunshield and supporting structures after separation from the rocket.

Webb extends astronomy beyond Hubble’s strengths. Its large mirror and infrared instruments allow scientists to examine distant galaxies, the formation of stars and planets, exoplanet atmospheres and objects within our own solar system. Infrared light is especially useful for studying cool objects and seeing through clouds of dust.

Webb operates about 1.5 million kilometers approximately 1 million miles from Earth near the second Sun–Earth Lagrange point, called L2. It does not sit motionless at one point and it does not orbit Earth in the same way as an ordinary satellite. Webb follows a large halo orbit around the L2 region while traveling around the Sun with Earth.

This geometry keeps the Sun, Earth and Moon on the same side of the observatory. Webb can keep its sunshield facing those heat sources while the telescope remains cold and looks outward into space. The orbit also provides broad access to the sky and continuous communication opportunities with Earth.

Webb’s primary mirror is approximately 6.5 meters, or 21.3 feet, across and is formed from 18 hexagonal, gold-coated beryllium segments. After deployment, actuators adjusted the segments so they could function together as one precisely shaped optical surface.

A five-layer sunshield roughly the size of a tennis court separates Webb’s warm spacecraft side from the cold telescope side. Cooling matters because warm objects emit infrared radiation. The observatory must reduce its own infrared glow so faint signals from space are not overwhelmed.

Webb’s four major instrument systems are NIRCam, NIRSpec, MIRI and FGS/NIRISS. Together they provide imaging, spectroscopy and precise guidance across near- and mid-infrared wavelengths.

Webb launched from Europe’s Spaceport in French Guiana at 12:20 UTC on 25 December 2021 aboard Ariane 5 flight VA256. About 27 minutes after liftoff, the observatory separated from the upper stage and deployed its solar array. It reached the L2 region and entered its planned orbit on 24 January 2022.

The launch had been targeted for 24 December, but adverse weather at the spaceport moved the attempt to 25 December. This is a documented weather delay, not an inferred scrub. Webb and the launch vehicle remained safe inside the final assembly building while teams reviewed the forecast.

As the universe expands, light from very distant objects is stretched toward infrared wavelengths. Webb’s sensitivity lets astronomers study galaxies whose light has traveled for billions of years. Infrared observations also penetrate some dusty regions where stars and planetary systems form.

Spectroscopy separates light into wavelengths, revealing information about temperature, composition and motion. When an exoplanet passes in front of its star, a small amount of starlight filters through the planet’s atmosphere. Webb can study that spectrum for evidence of particular molecules.