What is the James Webb Space Telescope?

NASA has released the first images from the James Webb Space Telescope, creating a stir across the planet. We make use of Earth satellites at Darwin, so our involvement with space is closer to home, but we’re still excited about this new glimpse into our universe. Here’s a quick look at the new space telescope.

What is a space telescope?

Space telescopes are used to observe and photograph space, but that’s not why they’re called space telescopes. To be a space telescope, a telescope needs to be in space.

It’s obviously difficult and expensive to establish a telescope in space, but it results in better-quality images of space. Earth’s atmosphere distorts the light that passes through it; this is why stars seem to twinkle when we look up at them from Earth. Because space telescopes are put into orbit above Earth’s atmosphere, they can avoid this distortion and take clearer photographs of what’s out there.

What is the James Webb Telescope?

As the name suggests, the James Webb Space Telescope is a space telescope. It was developed by multiple space agencies working together; NASA, ESA and CSA all had a role in its creation.

The James Webb Space Telescope was named after James Edwin Webb, who was the administrator of NASA between 1961 and 1968. It’s also known as JWST or Webb.

Webb was launched on Christmas Day in 2021 as the successor to the Hubble Space Telescope, launched in 1990, although the Hubble Space Telescope is expected to continue operating for the next few years. Webb is about half the weight of Hubble in Earth’s gravity, but it’s considerably larger, it’s much more powerful and it has a larger field of view. Webb was also designed with infrared photography in mind, whereas Hubble focuses more on the visible and ultraviolet spectrums.

Unlike the Hubble Space Telescope, which orbits the Earth, the James Webb Space Telescope orbits the sun. It’s about a million miles further from the sun than Earth, and it took a month to reach its orbital point, known as the Sun–Earth L2 Lagrange point (or simply L2), after its launch.

At L2, Webb is able to orbit in line with the Earth around the sun, meaning that the sun and the Earth are always in the same direction from Webb’s perspective. This is important because it means Webb’s sunshield can constantly face the Earth and sun, blocking their light and heat and preventing interference with Webb’s infrared detectors.

Because it’s so far from Earth, Webb was designed with the understanding that it wouldn’t be possible to visit it for repairs, whereas Hubble is in low Earth orbit and has been serviced on several occasions.

How do space telescopes see back in time?

It’s often mentioned that space telescopes can see the past. How is that possible?

Powerful telescopes can detect light from sources a great distance away, but that light takes time to travel across space. Light years are a measure of distance based on how long it takes light to travel that distance; for example, if a star is 20 light years from the telescope, that means its light reaches the telescope 20 years after it first left the star. In other words, what the telescope sees is what the star looked like 20 years ago. If a spaceship flew directly in front of the star, the telescope would only see the spaceship 20 years later.

This means that, strictly speaking, you can also see the past with your eyes. Light from the moon takes slightly over a second to reach the Earth, so, when you look up at the moon, you’re seeing it as it was a second ago. Rigel is one of the visible stars in Orion, so we’d notice if it exploded, but not for a while; it’s about 860 light years away, so we wouldn’t see the explosion for centuries.

If you were somehow on Rigel looking at Earth, 860 light years away, the Earth you saw would be the Earth of the twelfth century. If you had an excellent telescope, you might be able to see Henry II going about his business. A lot has happened on Earth since then, of course, but you would only be able to see the light that’s had the time to reach you.

For an example using a different sense, think about lightning. Thunder and lightning happen in the same instant; thunder is the sound of lightning. But, because light travels faster than sound, you’ll see the lightning from a nearby storm before you hear the thunder. When the thunder reaches you, you’re hearing a sound that occurred in the past; you know, from the fact you’ve already seen the flash of the lightning, that it’s not happening right now.

Essentially, the further away something is, the further in the past our perception of it is. Because a powerful telescope like Webb can see things that are hugely far away, it can also see things a long way in the past. Unfortunately, it’s not possible to control this; if a planet is a thousand light years away, Webb can see what it was like a thousand years ago, but it can’t see what it was like ten thousand years ago or what it’s like right now.

Even if Webb’s ability to see the past is limited in some ways, it’s still remarkable, and it may be able to give us more insight into the origins of the universe. We’re looking forward to seeing what it discovers.

Cover image: NASA, ESA, CSA, STScI

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