The most anticipated telescope of the century, the James Webb Space Telescope, will finally launch on Christmas Day. After several delays, budget overruns, and drastic changes in design, the telescope is all set to start its journey of being a time machine that will take us back to our origins. So to celebrate the upcoming launch of the legendary Webb, here’s a list of exciting things that you must know about the biggest space telescope built to date.

1. Webb wasn’t Webb initially

The planning for a giant telescope that could serve as a successor to the Hubble Space Telescope started in the 1990s. However, Hubble’s successor, which was supposed to go a notch higher than Hubble’s capabilities, was formerly known as the “Next Generation Space Telescope” (NGST). It was only in September 2002 that it was renamed after a former NASA administrator, James E. Webb. And the rest is history!

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James E. Webb

2. Webb is a time machine

Our universe is home to a wide range of frequencies, and human eyes are sensitive to only a tiny portion of this electromagnetic spectrum. Infrared photons have comparatively longer wavelengths than those of their visible counterparts. Infrared photons can have a wavelength ranging between 800 nm to 1 mm. In contrast, a photon belonging to the visible region can have its wavelength only between 300 nm to 800 nm.

Our universe is full of dense regions containing stellar dust. Stars and planets that have just started forming also lie hidden behind cocoons of dust. Even when we look at the Milky Way in the night sky, we see dark dust clouds obscuring much of the galaxy. This is because the interstellar dust absorbs most of the visible light due to its short wavelength photons.

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Electromagnetic spectrum and the satellites | Image: NASA

However, infrared rays, which are nothing but a signature of an object in the form of heat, have a longer wavelength than visible rays. Hence, the infrared light emitted by these regions can easily penetrate the dusty shroud and reveal what is inside. The farther a telescope can see, the more it can look back in time.

Now coming back to JWST, it has been configured to cover wavelengths from 0.6 to 28 micrometers. This will eventually help Webb look back over 13.5 billion years in time, thereby providing images of the first galaxies formed and observing unexplored planets around distant stars. And this is how the JWST will act like a time machine taking us back to our origins.

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3. Webb will be miles away from us

The Hubble space telescope orbits Earth and observes the cosmos at ~570 km above us. However, JWST is not going to be so close to our planet. It will not orbit the Earth. Instead, it will sit at the Earth-Sun L2 Lagrange point, 1.5 million km away.

There are five Lagrange Points, where gravity from the Sun and Earth balance the orbital motion of a satellite. Putting a spacecraft at any of these points allows the satellite to stay in a fixed position relative to the Earth and Sun. Moreover, minimal energy is needed for the satellite’s course correction.

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The five Lagrange points and the position of JWST | Image: NASA/WMAP Science Team

So when Webb is placed at the L2 point, its solar shield will block the light from Sun, Earth, and Moon, thereby helping to keep the telescope at a lower temperature. Moreover, even Sun’s infrared radiation won’t interfere with the deep space observations at this position. However, due to its large distance from Earth, JWST won’t enjoy the regular services that Hubble has been offered. In addition, no mission can take the astronauts to the L2 point and return them safely. Hence, once Webb is launched, it will be on its own.

4. Webb will be the coldest telescope in space

Unless an object has a temperature of absolute zero (-273°C), it will always emit infrared radiation. So, to have precise observations from Webb and to make sure that its infrared radiations don’t interfere with the signals received from deep space, Webb will be kept at significantly low temperatures.

Webb's gigantic sunshield
Webb’s gigantic sun shield | Image: Northrop Grumman/Goddard Space Flight Center

To achieve so, the JWST has a five-layer sun shield that is the size of a tennis court. It will weaken up the heat from the host star by more than a million times. This, in turn, will help JWST to stay cool, approximately up to -220°C. This is about 15 times lower than the temperature maintained at Hubble’s mirrors, making Webb the coldest active telescope in space.

5. James Webb Space Telescope vs Hubble Space Telescope

The James Webb Space Telescope is a successor of the Hubble Space Telescope. However, it is a lot different from its predecessor. Where Hubble mostly observed the cosmos in visible light, Webb will explore the cosmos in infrared light.

Even talking about their sizes, both the telescopes are drastically different. While the Hubble Space Telescope is about the size of a large school bus, the JWST is half as big as a 737 aircraft.  However, JWST weighs half as that of Hubble, but its primary collecting area is five times as large.


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Overall size comparison of Webb and Hubble | Image: GSFC

So yes, the James Webb Space Telescope is a masterpiece in itself. And once it’s launched, it will mark the beginning of a new era of astronomy. We wish Webb clear skies ahead!

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Prof. Bharat Kangude

Very interesting things to know. Thanks a lot.

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