What is the James Webb Space Telescope?

An introduction to the JWST
17 October 2023

Interview with 

Rosemary Williams


Artist's impression of the James Webb Telescope


Over the past 15 months, we’ve been treated to a new way of looking at the universe. Images of newly discovered galaxies, cosmic formations, and potentially habitable planets have been coming through faster, and in better detail, than ever before. All thanks to the James Webb Space Telescope.

The James Webb Space Telescope is a groundbreaking space-based observatory that was launched on Christmas day of 2021. It is the most powerful and advanced space telescope ever built, designed to explore the universe in ways never before possible.
It was designed to study the formation and evolution of galaxies, the birth of stars and planetary systems, the atmospheres of exoplanets, and potentially identifying signs of habitability or even life on other worlds. And, in the past 15 months, the JWST has been sending back incredible images of our universe, and fundamentally changing how we understand our place in the cosmos.

Unlike its predecessor Hubble that studied mostly visible light, JWST is primarily an infrared telescope, which makes it uniquely suited for studying objects and phenomena that emit infrared radiation, like distant galaxies, stars, and exoplanets. It orbits the Sun at the second Lagrange point, a point in space where gravity from the nearby Earth perfectly balances the gravitational pull of the distant (but massive) Sun. This point is just over a million miles from Earth, which allows it to avoid interference from our planet's atmosphere and stay cool, ensuring optimal infrared observations, whilst using a small amount of fuel. But unlike with space systems like the International Space Station or Hubble, astronauts will not be able to repair or upgrade the telescope. This meant everything needed to be perfect on launch.

The concept of a telescope like the JWST was pitched in 1989, and preliminary discussions even placed it on the moon! But the telescope's development was far from smooth sailing, and the launch was delayed 8 times between 2018 and 2021. The project even survived a threatened cancellation in 2011 due to the skyrocketing costs associated with being the most advanced piece of observational hardware ever put into outer space. It weighs 6,500 kg, with giant, eye-catching honeycomb-like mirrors that have become synonymous with the JWST. Each of these mirrors is 0.74 metres across, made of beryllium and coated in a layer of gold. The entire mirror system is made up of 18 of these hexagonal mirrors, carefully pieced together to form a larger mirror 6.5 meters in diameter, collecting and focusing 98% of the light it receives onto its suite of scientific instruments.

The James Webb Space Telescope has already begun to shake up what we thought we knew about the universe and its origins, and is poised to continue making profound contributions to astronomy and astrophysics for many years to come.


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