An artist's impression of the James Webb Space Telescope when unfolded

The James Webb Space Telescope is the largest ever built, and is designed to view the universe in infrared. Image © NASA GSFC/CIL/Adriana Manrique Gutierrez, licensed under CC BY 2.0 via Flickr

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James Webb telescope launched to view the early universe

The largest space telescope ever built has been launched as part of a mission to view the early years of the universe.

The launch of the James Webb Space Telescope in South America begins a six-month countdown to it becoming fully operational, after which it will start taking some of the most detailed pictures of the cosmos.

Humanity's new eye in the sky has been launched, promising to show us glimpses of the universe never seen before.

The James Webb Space Telescope, named after a former head of NASA, lifted off on Christmas Day on its journey into orbit, where it will take over from Hubble as the main scientific instrument examining deep space.

Astronomers hope that the new satellite will be able to capture black holes, peer through the atmospheres of planets and understand goings-on in distant galaxies. 

A man stands in front of part of the main mirror of the James Webb Space Telescope

The telescope's mirror measures 6.5 metres in diameter. Image © NASA/MSFC/David Higginbotham, licensed under CC BY 2.0 via Flickr

They do it with mirrors

Space telescopes are satellites pointed into space and designed to collect types of radiation including light, X-rays and infrared. The first were launched in the late 1960s and early 1970s, aiming to capture images of the universe without Earth's atmosphere in the way.

Perhaps the most famous space telescope is Hubble, which launched in 1990. After issues with its lens were corrected, the telescope gave scientists some of the most spectacular images of the cosmos.

Even before Hubble was launched, scientists were discussing what would come next for space observation. One particular limitation of Hubble was that it was designed to fit inside the head of a rocket, restricting its size.

A larger mirror allows greater amounts of light to be gathered and focused in the telescope. The larger the mirror, the more likely that even the faintest traces of distant galaxies and other space objects will be detected.

While Hubble's mirror, at 2.4 metres, is big, scientists wanted to create an even larger telescope. With Webb, they will have a mirror around 6.5 metres in diameter, made of 18 individual segments. These will fold so that it can be launched in a conventional rocket and can adjust itself as instructed in space.

The collapsible design, however, means the mirror is left open to space where sunlight would obscure its observations if left unchecked. To account for this, a sunshield the size of a tennis court will also unfold to block out the Sun's rays and keep the telescope cool while a solar panel behind it will generate electricity.

Webb will also go much further from Earth than Hubble. The new telescope will travel 1.6 million kilometres from our planet into a Lagrange point, where the Earth and the Sun's gravity, along with its orbital momentum, will help keep it in one place without using up much fuel.

In about six months' time, after arriving at its new home and being set up, Webb will be ready to start looking into the farthest reaches of the universe.

Engineers prepare to load the James Webb Space Telescope into an Ariane 5 rocket

James Webb is designed to unfold in space, allowing it to be larger than previous telescopes. Image © ESA-M.Pedoussaut, licensed under CC BY 2.0 via Flickr

Peeking behind the cosmic curtain

The Webb telescope is designed to view the world in infrared, as opposed to the visible and ultraviolet focus of Hubble. NASA says that the sensors are so sensitive it could detect the heat signature of a bumblebee at almost 400,000 kilometres away.

Rather than looking at extra-terrestrial insects, however, the telescope will focus on specific parts of the infrared spectrum that are less absorbed by dust and other particles, allowing scientists to look through dense clouds and atmospheres.

One task using these sensors will have is investigating the make-up of the most common planets in the galaxy. While most stars have the exoplanets, called sub-Neptunes, in orbit around them, there are none in our solar system.

Sub-Neptunes are smaller than the eponymous planet, but orbit very close to their stars. Particles in their atmosphere obscure the ways in which scientists infer the make-up of these sub-Neptunes, but infrared should be able to peer through the haze.
Another reason to focus on infrared light is to look further back into the past than ever before. As the universe expands, visible light from the earliest stars is stretched through a phenomenon known as redshifting into the infrared spectrum.

It is hoped that Webb will be able to see into a mysterious time known as the Epoch of Reionisation as the universe changed from being full of opaque gases into its current transparent form. It's also the time when the first galaxies formed, offering the chance to discover how the universe as we know it came into being.

Further projects will help find out more about the black hole at the centre of the Milky Way, understand the conditions that stars need to form, as well as hunting for other Earth-like planets.

We'll learn in the following days and months whether or not Webb's mission goes as planned, and if it can launch a new chapter in our understanding of the universe.