James Webb Space Telescope Explained: Where It Is and What It Sees
A plain-English guide to the James Webb Space Telescope: why it orbits a point beyond the Moon, why it sees in infrared, and how its pictures go from raw data to official releases.
The James Webb Space Telescope (JWST) is an infrared space observatory run by NASA with the European Space Agency and the Canadian Space Agency. It launched on Dec. 25, 2021, and orbits the Sun near the second Lagrange point (L2), about 1 million miles (1.5 million km) from Earth. Its official images are released by NASA, ESA and the Space Telescope Science Institute.
What does the James Webb Space Telescope do?
Webb studies the universe in infrared light, which lets it see the first galaxies, the inside of dust clouds where stars form, and the atmospheres of planets around other stars. NASA says it can look back more than 13.5 billion years, to galaxies that formed not long after the Big Bang.
Its main science areas are:
- The early universe and the first galaxies.
- How galaxies grow and change over billions of years.
- The birth of stars and planetary systems inside dusty nebulas.
- Exoplanets, including the chemistry of their atmospheres.
- Objects in our own solar system, from Mars and the giant planets to comets and Kuiper Belt objects.
Where is the Webb telescope now?
Webb orbits the Sun around L2, a balance point about 1 million miles from Earth on the side facing away from the Sun. It arrived there on Jan. 24, 2022. At L2, the Sun, Earth and Moon all stay on one side of the telescope, so a single sunshield can block their heat and light at all times.
Webb does not sit still at L2. It travels in a large halo orbit around that point, which keeps it out of Earth’s shadow and in steady contact with ground stations. By comparison, the Hubble Space Telescope orbits only a few hundred miles above Earth. Our explainer on how orbits work covers the difference between low orbits and distant ones.
Why does Webb see in infrared?
Webb works in infrared because light from the most distant galaxies has been stretched to longer, redder wavelengths during its 13-billion-year trip, and because infrared light passes through dust that blocks visible light. Hubble sees mainly visible and ultraviolet light, so the two telescopes complement each other.
Infrared telescopes must be very cold, or their own heat would swamp the faint signals. Webb’s five-layer sunshield, about the size of a tennis court, keeps the mirror and instruments at around minus 370 degrees Fahrenheit. The mid-infrared instrument has an extra cooler to go colder still.
| Feature | James Webb Space Telescope | Hubble Space Telescope |
|---|---|---|
| Launched | Dec. 25, 2021, on an Ariane 5 from French Guiana | April 24, 1990, on space shuttle Discovery |
| Location | Orbit around L2, about 1 million miles away | Low Earth orbit, a few hundred miles up |
| Main mirror | 6.5 m (21.3 ft), 18 gold-coated segments | 2.4 m (7.9 ft), single mirror |
| Light it sees | Near- and mid-infrared | Ultraviolet, visible and near-infrared |
| Partners | NASA, ESA, CSA | NASA, ESA |
| Can be serviced by astronauts? | No | Yes, five shuttle servicing missions flew |
What instruments does Webb carry?
Webb carries four science instruments, each with cameras, spectrographs or both:
- NIRCam (Near-Infrared Camera), the main imager, built by the University of Arizona and Lockheed Martin.
- NIRSpec (Near-Infrared Spectrograph), provided by ESA, which can take spectra of up to about 100 objects at once.
- MIRI (Mid-Infrared Instrument), built by a European consortium and NASA’s Jet Propulsion Laboratory, for cooler and dustier targets.
- NIRISS with the Fine Guidance Sensor, provided by the Canadian Space Agency, used for exoplanet work and pointing.
Spectra matter as much as pictures. Splitting light into its colors reveals which molecules, such as water, carbon dioxide or methane, are present in a planet’s atmosphere or a distant galaxy.
How are Webb’s images released, and where can you find the latest ones?
Official Webb images come out through NASA, ESA and the Space Telescope Science Institute (STScI) in Baltimore, which runs the telescope’s science operations. Each release includes a processed color image, a caption explaining what is shown, and credits.
- Go to NASA’s Webb mission page for news and the image gallery, which you can filter by topic.
- Check STScI’s webbtelescope.org and ESA’s esawebb.org for the same releases, often with full-resolution downloads.
- For raw data, search the public Mikulski Archive for Space Telescopes (MAST). Many observations become public right away, and others after an exclusive period for the scientists who proposed them, typically up to 12 months.
Webb’s colors are assigned. Because the telescope sees infrared light that human eyes cannot, image processors map each infrared filter to a visible color, usually with shorter wavelengths shown as blue and longer ones as red. Captions list which filters were used. Our guide on how to follow NASA missions covers alerts and official feeds for new releases.
How long will Webb last?
Webb was designed for a science mission of at least five years, with a goal of ten. After launch, NASA said its precise trajectory left enough propellant to support science operations for significantly more than ten years. Because it orbits so far away, Webb cannot be repaired by astronauts, so its lifetime depends on fuel for keeping its orbit and on the health of its parts. Small meteoroid hits on the mirror have been expected and recorded since launch.
Bottom line
Webb is the largest infrared telescope in space, orbiting near L2 about 1 million miles from Earth since January 2022. It studies early galaxies, star formation and exoplanet atmospheres, complementing Hubble’s visible-light view. The newest official images appear on NASA’s Webb pages, webbtelescope.org and esawebb.org, and raw data is public through MAST.
FAQ
Can you see the James Webb Space Telescope from Earth?
Not with the naked eye or ordinary binoculars. At about 1 million miles away and with its dark sunshield, Webb is far too faint. Some advanced amateur astronomers have photographed it as a faint dot through large telescopes.
Is Webb a replacement for Hubble?
No. Webb was built to look deeper in infrared light, while Hubble covers ultraviolet and visible light. Both telescopes operate at the same time, and some studies combine their data.
Who decides what Webb looks at?
Astronomers worldwide submit proposals, and expert panels choose the programs for each annual cycle. STScI schedules the observations, with some time set aside for the partner agencies and the teams that built the instruments.
Why are Webb images so detailed?
Webb’s 6.5-meter mirror collects far more light than earlier space telescopes, and its infrared cameras are very sensitive. Long exposures and careful processing combine many frames into one high-resolution picture.
