What Is the James Webb Space Telescope?
The James Webb Space Telescope (JWST) is the largest, most powerful space telescope ever built. Launched on December 25, 2021, and beginning science operations in 2022, Webb observes the universe in infrared light — the same kind of light our eyes cannot see but that penetrates cosmic dust and reveals the universe's oldest, most distant objects.
Webb is an international partnership between NASA, the European Space Agency (ESA), and the Canadian Space Agency (CSA), designed to see farther back in time than any telescope before it.
How Does Webb Work?
Webb's primary mirror is 6.5 meters across, made of 18 gold-coated beryllium hexagonal segments that unfold in space. Gold maximizes the mirror's reflectivity of infrared light. A tennis-court-sized sunshield blocks heat from the Sun, Earth, and Moon, cooling Webb's instruments to near absolute zero so they can detect faint infrared signals.
Because infrared light is essentially heat, Webb must be kept extremely cold; otherwise its own warmth would blind its sensors. The sunshield and its distant orbit make that possible.
Why Does Webb Orbit at L2?
Webb does not orbit Earth like Hubble. Instead it circles the Sun at the second Lagrange point (L2), about 1.5 million kilometers away, where the gravity of the Sun and Earth balance in a way that lets the telescope maintain a stable position relative to both. From L2, Webb can keep its sunshield pointed at the Sun, Earth, and Moon simultaneously while observing deep space.
What Has Webb Discovered?
Webb has confirmed some of the oldest galaxies ever seen, formed just 300 million years after the Big Bang — a window into the cosmic dawn. It has studied exoplanet atmospheres, detecting water vapor and carbon dioxide on distant worlds. It has revealed star-forming nebulae in stunning detail and imaged planets in our own solar system with new clarity.
These discoveries show that the early universe assembled galaxies faster than expected, reshaping models of cosmic evolution.
Webb vs. Hubble: What's the Difference?
Hubble observes mostly in visible and ultraviolet light from low Earth orbit; Webb observes in infrared from L2. Hubble excels at sharp visible-light images of nearby objects, while Webb sees through dust and reaches the infrared-dark early universe. The two telescopes are complementary, and combining their data gives astronomers a fuller picture.
Key Takeaways
- Webb is the largest, most powerful space telescope ever built
- It observes in infrared light, piercing dust and revealing the early universe
- Its 6.5 m golden mirror and sunshield keep instruments extremely cold
- It orbits the Sun at L2, 1.5 million km from Earth
- Major discoveries include the oldest galaxies and exoplanet atmospheres