In July 2022, the world got its first look at pictures from the James Webb Space Telescope, and the reaction was almost universal: wow. Glittering galaxies stretched and curved across the frame, glowing cliffs of cosmic dust towered like mountain ranges, and a dying star blew out delicate shells of gas in colours no one had seen before. For many people, it felt like seeing the universe for the first time.
But the James Webb Space Telescope, often shortened to JWST or simply Webb, is much more than a camera that takes pretty pictures. It is one of the most complex machines humans have ever built, designed to look back more than 13 billion years and answer some of the biggest questions in science. Where did the first stars and galaxies come from? How do planets form? Are there other worlds with the right conditions for life?
In this guide, we will explain how Webb works in simple terms and look at some of its most exciting discoveries so far. No science background is needed, just a bit of curiosity.
What Is the James Webb Space Telescope?
The James Webb Space Telescope is a large space observatory built by NASA together with the European Space Agency (ESA) and the Canadian Space Agency (CSA). It was launched on 25 December 2021 from French Guiana on an Ariane 5 rocket, after more than two decades of planning, building, and testing. It is named after James E. Webb, who led NASA during the 1960s when the Apollo programme was getting underway.
Webb is often called the successor to the famous Hubble Space Telescope, but that is not quite accurate. A better description is that it is Hubble’s partner, designed to see the universe in a different kind of light. Hubble mostly sees visible and ultraviolet light, the kinds of light our eyes can detect, while Webb is built mainly to see infrared light.
That difference might sound small, but it changes everything, as we are about to see.
Why Infrared? Seeing the Invisible
Light comes in many different types, from radio waves to visible light to X-rays. Our eyes can only see a small slice of this range. Infrared light has slightly longer wavelengths than the red end of the visible rainbow, and we cannot see it, although we can feel it as heat. When you hold your hand near a warm cup of tea, you are sensing infrared radiation.
There are three big reasons why infrared is so valuable for astronomers.
1. Looking back in time. Light takes time to travel across space, so when we look at a faraway galaxy, we see it as it was long ago. The most distant galaxies are also moving away from us as the universe expands, and this stretches their light to longer wavelengths, a process called redshift. Light that left some of the earliest galaxies as visible or ultraviolet light arrives at us stretched into the infrared. So to see the first galaxies, we need an infrared telescope.
2. Peering through dust. Space is filled with clouds of dust that block visible light, hiding newborn stars and forming planets inside them. Infrared light can pass through much of this dust, like a torch beam through a thin mist. This lets Webb see right into the nurseries where stars are born.
3. Detecting cool objects. Cooler objects, such as planets, brown dwarfs, and distant dust clouds, glow mostly in infrared. Webb can detect them even when they give off hardly any visible light.
How Does Webb Work? The Key Parts
Webb looks complicated, but its design can be understood through a few main parts.
The Giant Golden Mirror
The heart of Webb is its huge primary mirror, which is 6.5 metres wide, more than two and a half times the width of Hubble’s 2.4-metre mirror. A bigger mirror collects more light, just like a bigger bucket catches more rain, and Webb’s collects roughly six times as much as Hubble’s. This allows it to see fainter and more distant objects.
A mirror this big could not fit inside any rocket, so engineers built it from 18 hexagonal segments, each about 1.3 metres across, made of a light but very strong metal called beryllium. Each segment is coated with an extremely thin layer of gold, just about 100 nanometres thick, because gold reflects infrared light exceptionally well. The whole mirror was folded up like origami for launch and unfolded in space.
Once in space, tiny motors behind each segment adjusted its position with incredible precision, down to a fraction of the width of a human hair, so that all 18 pieces work together as a single, perfect mirror.
The Sunshield
Here is a challenge. Infrared telescopes detect heat, so if the telescope itself is warm, its own heat would drown out the faint signals from distant space. It would be like trying to see a candle while standing next to a bonfire. Webb therefore has to be extremely cold.
The solution is a giant sunshield about the size of a tennis court, roughly 21 metres by 14 metres. It is made of five super-thin layers of a special plastic-like material coated with aluminium, each layer about as thin as a human hair. The layers are spaced apart so that heat becomes trapped and radiated away between them.
The result is remarkable. On the side facing the Sun, temperatures can reach about 85°C. On the shaded side where the instruments sit, they drop to about -233°C. That is a temperature difference of over 300 degrees across just a few metres. One of the instruments, called MIRI, is cooled even further with a special cooler, to around -266°C, only a few degrees above absolute zero.
The Scientific Instruments
Behind the mirror sits a compact set of instruments that turn the collected light into data. The main ones are:
- NIRCam, the near-infrared camera, which takes the sharp, colourful pictures of galaxies and stars. It also helps keep the mirror aligned.
- NIRSpec, a near-infrared spectrograph, which splits light into its different colours to reveal what objects are made of, how hot they are, and how fast they are moving.
- MIRI, the mid-infrared instrument, which sees longer infrared wavelengths and is excellent for studying cool dust, newborn stars, and distant planets.
- NIRISS and the Fine Guidance Sensor, which help with imaging, spectroscopy, and keeping the telescope pointed precisely at its targets.
A spectrograph is worth a special mention. When light from a star or planet is split into a rainbow, dark lines appear at specific colours, like a barcode. Each chemical element or molecule leaves its own unique pattern, so by reading the barcode, scientists can tell what an object is made of, even from trillions of kilometres away.
The Spacecraft Bus
The telescope is powered and steered by a part called the spacecraft bus, which holds solar panels, communication systems, and small thrusters. The solar panels always face the Sun, and the antenna sends data back to Earth, where it is received by NASA’s Deep Space Network.
Where Is Webb? A Special Parking Spot in Space
Unlike Hubble, which orbits Earth only about 540 kilometres above the surface, Webb sits about 1.5 million kilometres from Earth, roughly four times the distance to the Moon. It is parked at a special spot called the second Lagrange point, or L2.
At L2, the gravity of the Sun and Earth combine in such a way that a spacecraft can stay in a steady position relative to both, orbiting the Sun in step with Earth. This provides three big advantages. The Sun, Earth, and Moon are all in the same direction, so a single sunshield can block all three. The telescope stays at a steady cold temperature. And Webb has a clear, unobstructed view of deep space most of the time.
The downside is that Webb is too far away for astronauts to repair, unlike Hubble, which was serviced five times. That is why Webb had to work perfectly from the start, and thousands of parts had to unfold without a single failure.
The Journey: A Month of Nail-Biting Unfolding
After launch, Webb spent about a month travelling to L2 while unfolding itself in space. Engineers famously called this stage the “29 days on the edge,” because it involved hundreds of steps that all had to work, with no chance of fixing anything if something went wrong. The sunshield alone had to unfold and tension five layers using hundreds of release mechanisms.
Everything went remarkably well. By January 2022, the mirror and sunshield were fully deployed, and over the following months the instruments cooled and the mirror segments were carefully aligned. In July 2022, NASA released the telescope’s first full-colour images and spectroscopic data, and the world got to see what Webb could do.
Webb was even better than expected. It also uses so little fuel for course corrections that it is expected to operate for more than 20 years, far longer than the original goal of about 10 years.
What Has Webb Discovered? The Highlights
Now for the exciting part. In just a few years, Webb has changed what we know about the universe. Here are some of its most notable discoveries and images.
Webb’s First Deep Field
The first image released was a view of a galaxy cluster called SMACS 0723. The cluster’s huge gravity acts like a cosmic magnifying glass, bending the light of galaxies behind it, in an effect called gravitational lensing. The result was a crowded scene of thousands of galaxies, including some of the most distant ever seen up to that time, with tiny arcs and smears of light that had travelled for over 13 billion years. NASA described the patch of sky as being about the size of a grain of sand held at arm’s length.
Galaxies That Are Too Early, Too Bright, and Too Big
One of Webb’s most surprising findings is that the early universe seems to have been busier than scientists expected. Webb has found galaxies that existed only a few hundred million years after the Big Bang, which is when the universe was less than 3 percent of its current age. Some of these record-breaking galaxies are from around 300 million years after the Big Bang.
What surprised astronomers was how bright, mature, and numerous some of these early galaxies appear. Many look more developed than models predicted, which means that star formation and galaxy growth may have started faster than we thought. Scientists are now refining their ideas, and this is a good example of science working as it should: new evidence leads to better theories. Some early results suggested a few of these galaxies were so massive that they challenged the standard picture, but follow-up studies have shown that many can be explained with adjustments, such as stars forming very efficiently in the early cosmos.
Mysterious “Little Red Dots”
Webb has also revealed a population of small, very red, compact objects in the early universe, nicknamed “little red dots.” Their true nature is still debated. Some may be young black holes feeding on gas, others may be unusually compact galaxies, and scientists are still working to understand them.
Studying the Atmospheres of Other Worlds
Perhaps the most exciting part of Webb’s work is on exoplanets, which are planets orbiting stars other than our Sun. When an exoplanet passes in front of its star, a small amount of starlight filters through its atmosphere. By splitting that light with a spectrograph, Webb can identify the gases in the atmosphere.
Here are some highlights:
- Water vapour on WASP-96b. In its very first data release, Webb detected clear signs of water vapour, clouds, and haze in the atmosphere of this hot, puffy gas giant.
- Carbon dioxide on WASP-39b. Webb provided the first clear detection of carbon dioxide in the atmosphere of an exoplanet, as well as evidence of chemical reactions driven by starlight in its atmosphere.
- Rocky planets of TRAPPIST-1. This nearby star hosts seven roughly Earth-sized planets. Observations of the innermost ones suggest they have little or no thick atmosphere, which is valuable information about whether rocky planets around small red stars can hold on to air.
- A direct look at planets. Webb has also directly photographed some giant exoplanets by blocking out the light of their parent stars, a feat that is extremely difficult.
It is important to be honest about the limits. Webb has not found life elsewhere, and claims of possible biosignatures, such as a hint of certain molecules in the atmosphere of a planet called K2-18b, remain debated and need much more evidence. Even so, Webb is giving us a way to study planets that was impossible before.
Stunning Views of Star Birth
Webb’s images of stellar nurseries have been some of its most beautiful. The Cosmic Cliffs in the Carina Nebula show a glowing wall of gas and dust where new stars are being born, sculpted by radiation from young stars. Webb also revisited the famous Pillars of Creation, first made famous by Hubble, and its infrared view revealed hundreds of newly formed stars hidden inside the dusty columns.
The Death of Stars
Webb has also beautifully captured the later stages of stellar life. The Southern Ring Nebula, a planetary nebula, appeared in extraordinary detail, showing a dying star surrounded by shells of gas, along with a second faint companion star that had been hidden before. Webb also imaged the remains of the supernova Cassiopeia A, revealing intricate structures in the expanding debris.
Galaxies in Action
The telescope’s image of Stephan’s Quintet, a group of five galaxies, showed galaxies interacting and colliding, with shock waves and star formation triggered by the encounters. It also produced a detailed view of a galaxy outflow from a distant supermassive black hole, and helped scientists study how black holes grew in the early universe.
Our Own Solar System
Webb is not only for faraway objects. It has also taken stunning images of our solar system’s giant planets, including Jupiter’s auroras, Saturn’s rings, and the faint rings of Uranus and Neptune, which were seen in detail for the first time in decades. It can also study icy objects and moons, such as Saturn’s moon Enceladus, whose geysers it has observed.
Hubble and Webb: Teammates, Not Rivals
Some people wonder whether Webb makes Hubble obsolete. It does not. They complement each other beautifully. Hubble sees in visible and ultraviolet light, which is best for certain details of stars, galaxies, and planets, while Webb sees in infrared, which is better for the oldest galaxies, hidden star nurseries, and cool objects. When astronomers combine data from both telescopes, they get a more complete picture, like seeing a scene in both daylight and thermal vision.
Webb at a Glance
| Feature | Hubble | James Webb |
|---|---|---|
| Main mirror size | 2.4 metres | 6.5 metres |
| Main light type | Visible and ultraviolet | Infrared |
| Location | Orbits Earth (about 540 km up) | At L2, about 1.5 million km away |
| Launch | 1990 | 2021 |
| Can astronauts repair it? | Yes (serviced five times) | No |
Challenges Webb Has Faced
Webb’s journey was not smooth from the beginning. The project took decades, faced delays and budget increases, and ended up costing around 10 billion US dollars. Some people questioned whether it was worth it. After its success, many scientists argue that the investment has paid off in discoveries.
Even in space, Webb has met small hazards. In 2022, a micrometeoroid, a tiny speck of space dust moving at high speed, struck one of the mirror segments. The telescope’s performance remained excellent, but it reminded engineers that space is a rough neighbourhood, and the mirror will slowly pick up more tiny dings over the years.
What Comes Next?
Webb is only getting started. Scientists around the world compete for observing time, and many projects are underway, including mapping more of the early universe, studying how planets form in young star systems, and examining more rocky exoplanets to see whether they have atmospheres.
Future telescopes, such as NASA’s Nancy Grace Roman Space Telescope and ESA’s missions, will build on Webb’s findings. Together, they could help answer one of humanity’s oldest questions: are we alone?
How You Can Explore Webb’s Images Yourself
You do not need to be a scientist to enjoy Webb’s work. Here are some easy ways to take part:
- Visit the official websites. NASA, ESA, and the Space Telescope Science Institute publish all of Webb’s new images for free.
- Look closely at the details. Webb’s pictures have spikes around bright stars. These eight-pointed “diffraction spikes” are a signature of its hexagonal mirror design.
- Remember the colours are chosen. Infrared light is invisible, so scientists assign visible colours to different wavelengths. Typically the longest wavelengths are shown as red and the shortest as blue, so the pictures are real data, translated into colours we can see.
- Follow the news. Space agencies regularly share new discoveries, and you can sign up for updates.
- Share your excitement. Talk about the images with friends or children. A single photo from Webb can start a great conversation about the universe.
A Gentle Final Thought
The James Webb Space Telescope is a symbol of what people can accomplish when they work together, patiently and creatively, over many years. Thousands of scientists, engineers, and technicians from many countries built a machine that unfolded itself a million and a half kilometres away and opened a new window on the cosmos.
You do not need to understand every detail of how it works to feel the wonder of what it shows us. Every new image is a reminder that the universe is vast, ancient, and full of surprises, and that we are lucky to live in a time when we can look back at its earliest light. Keep looking up, keep asking questions, and let Webb’s discoveries inspire your own curiosity.