The James Webb Telescope

A time machine that will help answer the secrets of the universe

On December 25, 2021, NASA’s three-decade-long effort culminated in the much-awaited launch of its newest and most ambitious telescope yet: the James Webb Telescope. This 10 billion dollar project was first discussed in 1990 with the goal of helping us better understand our universe. More than 30 years later, despite several budgeting scares and revisions to its design, the final telescope has been successfully constructed (1). The James Webb Telescope (JWT), is 100 times more powerful than its predecessor, the Hubble Space Telescope. Now in space, JWT has unparalleled advancements that could help answer some of the largest questions about how galaxies, planets, and life developed (2).

 The telescope’s appearance is best known for its signature golden primary mirror and its impressive dimensions. Its 6.1-meter tall primary mirror is constructed by 18 hexagonal segments, each with a 1.32m diameter. Its sun shield, a region of the telescope which protects it from overheating, has 21m by 14m dimensions. Even though it is much larger than Hubble, JWT is 131kg lighter (2). Due to their unique geometry, the primary mirror and sun shield are foldable. This allowed for easy transport aboard the Ariane-5 ship which was launched from French Guiana. 

Many consider the JWT a time machine, and in some ways this is true. The Webb telescope is predicted to be able to see light from 13 billion years ago, which is a quarter of a billion years after the Big Bang (3). This is because light takes time to travel. For example, light takes about 1.3 seconds to travel from the moon to Earth, so we see the surface of the moon how it was 1.3 seconds ago. As a result, the farther objects are, the longer it takes for light to travel, and the further back in time we can see. 

The telescope is made up of a myriad of tools. Its largest elements are the primary and secondary mirrors whose role is to gather the light which will later be analyzed and studied. The more light collected, the more clear and precise the images will be. Since the universe is expanding, visible light lengthens and becomes infrared light as it travels through space. This phenomenon is called redshift and is why the telescope is meant to operate using infrared light. Collecting infrared light is also advantageous because it can penetrate through dust clouds which are especially common around new forming planets.

Once the light is collected, it is passed to the second mirror which reflects it to the scientific instruments. Eventually, this light is focused into infrared detectors, where the light photons are transformed into a voltage. During this step, light is analyzed by tools that extract data from it. There are four major tools:

The first is called the Near-Infrared Camera (NIRCam) and is the primary imager for short-range infrared waves (0.6 µm – 5 µm). It allows for imaging, limited spectrography, and Coronagraphs which are especially important for exoplanet studies. Spectrography uses spectrographs, instruments that spread light onto a spectrum to extract information about a given object. Meanwhile, Coronagraphs help the telescope identify objects by blocking bright light sources that outshine them. It does so by placing black circles on top of bright objects (4). 

A Coronagraph placing dark circles on top of bright objects to focus on objects around the bright object (1).

The second tool, the Near-Infrared Spectrograph (NIRSpec), enhances the use of spectrography by extracting information about the temperature, atmosphere, and chemical composition of the object of interest (0.6 µm – 5 µm). In order to gather this information about an object, the telescope has to be focused on it for more than 100 hours (2). A shutter system is used once again to filter out irrelevant light.

The third tool is the Near-Infrared Imager and Slitless Spectrograph (NIRISS), which increases focus and helps capture images of improved quality. 

Lastly, the fourth tool is the Mid-Infrared Instrument (MIRI). It works with local infrared waves (4.9 µm – 28.8 µm), meaning that it can penetrate very close dust clouds. For this system to function, it has an ideal temperature of 6.7 Kelvin, which is why an internal cooling system is needed.

After its long and strenuous development, millions of scientists and enthusiasts are excited to see JWT at work. However, the telescope is not able to make use of these exciting advancements yet. Half of its first year in space will be spent finishing its travels and calibrating its equipment. While the Hubble telescope lies 340 miles away from Earth, JWT will travel nearly 1 million miles away from earth to a location called the Lagrange Point 2 or L2. This location is one of five places in our solar system where the “the gravitational pull of two large masses precisely equals the centripetal force required for a small object to move with them”; this means that the object is able to stay put (5,6). At the same time, it is an optimal location to limit the radiation from the sun and moon that could possibly skew the data.

Two weeks after its launch, the Webb telescope is set to unfold. About one month after its launch, the telescope is set to reach L2. From that point on, the telescope will calibrate itself and slightly adjust the placement of its hexagonal segments. These segments have a sensitivity of 1 to 10,000 to increase precision. Once this has occurred, the Webb is ready to take its first pictures (2).

As of January 24, 2022, the Webb has reached L2. Within the next few months, we will see Webb prepare to begin its work (5). 

NASA has announced General Observer opportunities where scientists can investigate targets using Webb’s technology during its first year in orbit in addition to NASA’s plans. More than 1000 proposals were sent in by scientists from over 44 countries, and 286 proposals have been selected. The telescope will spend its time learning about galaxies, exoplanets, stellar astrophysics, and our solar system (7,2).

Scientists are hopeful that the Webb telescope will help us understand the early history of our universe, from its first stars to how our universe functions.

1. Bartels, Meghan. “30 Years and $10 Billion Later, the James Webb Space Telescope Is Finally on the Launch Pad.” Accessed January 23, 2022.

2. The James Webb Space Telescope Explained in 9 Minutes. Produced by Perception. 2021.

3. Webb Space Telescope. Accessed January 23, 2022.

4. Space Telescope Science Institue. “Tools for Capturing the Cosmos.” Webb Space Telescope. Accessed January 23, 2022.

5. “Where Is Webb?” NASA, GODDARD SPACE FLIGHT CENTER. Accessed January 23, 2022.

6. NASA/WMAP Science Team. “What Is a Lagrange Point?” NASA.

7. “NASA’s James Webb Space Telescope General Observer Scientific Programs Selected.” NASA, March 30, 2021. Accessed January 23, 2022.

8. Shivaram, Deepa. “NASA’s James Webb Telescope Completes Its Final Unfolding in
Space.” NPR. Accessed January 23, 2022.