Artist concept of James Webb Space Telescope

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James Webb Space Telescope launch date, time, and how to watch NASA’s livestream

Here’s what you need to know.

Adriana Manrique Gutierrez, NASA Animator

The James Webb Space Telescope’s time is, finally, here (we think). After years of delays and setbacks, almost getting scrapped by Congress, and some extremely tricky and precarious maneuvers, the telescope is set to launch later this month. If it happens, it will be the launch of the decade — and you can watch it live.

This multi-billion-dollar observatory is a collaborative effort between NASA, the ESA, and the Canadian Space Agency. It will transform the field of space science, fuel the careers of thousands of astrophysicists and astronomers for the next century, and alter our perspective on the universe, both visually and scientifically. Here’s everything you need to know about the telescope and how to watch the launch next week.

James Webb Space Telescope: launch date and time

The Ariane5 is a reliable rocket that NASA has used multiple times to send critical science missions to space.Ariane/NASA

The James Webb Space Telescope (JWST, or Webb for short) is scheduled to launch on December 25, 2021, at 7:20 Eastern Standard Time. That date was moved from December 24 due to weather issues in French Guiana.

It will blast off from French Guiana aboard an Ariane 5 ECA rocket, headed for an orbit around the second Lagrange point, or L2, where the gravitational pull of Earth is equal to the gravitational pull of the Sun.

Webb’s launch has to be carefully timed to put the telescope on the right path. It needs to leave Earth when our planet’s axis is tilted in the right direction, and when the launch site is pointed toward the right area of space. In other words, the James Webb Space Telescope launch has to happen during the right season and at the right time of day. On launch day, those requirements allow just a 30-minute window in which Webb will have to launch — or it will have to wait for another day.

How to watch the James Webb Telescope launch livestream

You can watch the James Webb Space Telescope launch on NASA’s live-streaming channel, NASA Live.

After the rocket clears the launch pad, watch for a few major timestamps:

  1. About 206 seconds after liftoff, the fairing that protects the space telescope from the wind and friction of launch will open, exposing Webb to space for the first time.
  2. Shortly after this happens, Webb should send its first communications to operators on the ground.
  3. At 28 minutes after liftoff, Webb will separate from the launch vehicle.
  4. Between 31 and 33 minutes after separation, the telescope’s solar array will extend and begin powering Webb’s systems.

When will the James Webb Space Telescope be operational?

The James Webb Space Telescope won’t start studying the universe until around 6 months after the launch. Part of the reason why is because of where the Webb will lie in space — the telescope will take 29 days to reach its orbital point, which is a million miles from Earth.

NASA calls this the “29 days on the edge” because of how many important things have to go right in order for Webb to reach its permanent parking spot — which is also known as Lagrange Point 2 — in one, operational, piece.

A little more than two days after launch, the telescope will soar by the Moon, soundly beating the Apollo missions’ travel time by about 8 hours. Twelve days post-launch, the telescope’s primary mirror will begin to unfold. After that, it will take a further ten days to move all 18 mirror segments into their correct positions, and Webb’s operators on Earth will spend the next few months fine-tuning their alignment.

Once at its post, further system checks and adjustments will take another five months to complete. Only then can the telescope begin collecting data and images of the cosmos for us to marvel at on Earth.

What will the James Webb Space Telescope discover?

The James Webb Space Telescope’s mirrors will enable scientists to discover new secrets of the distant cosmos.Emmett Given, NASA Marshall

The James Webb Space Telescope is designed to study how galaxies, stars, and planets form. It will collect infrared images of some of the cosmos’ most ancient stars and galaxies, some of which formed 13.6 billion years ago (or about 200 million years after the Big Bang). It will also peer at newborn stars as they coalesce in nearby clouds of gas and dust.

At the same time, the telescope may detect potentially habitable planets around other stars in our galaxy. The telescope is powerful enough to discern exactly what gases are in the atmospheres of exoplanets as they pass in front of their host stars on their orbital paths. As it can image objects in infrared, the telescope may be particularly capable of discovering new details about distant gas giant planets — similar to Jupiter — orbiting other stars.

James Webb Space Telescope vs. Hubble Telescope

Hubble has done some deep-field studies of the early universe, and Webb will expand on that scientific knowledge.

The James Webb Space Telescope is often billed as the successor to Hubble, which was originally intended to spy on the cosmos for just 15 years. Now, Hubble has revolutionized our understanding of the universe for more than three decades — and the James Webb Space Telescope will certainly build on the wealth of scientific discovery enabled by Hubble.

The telescope will view much more distant objects than Hubble is capable of seeing. And while Hubble views the universe in the optical and ultraviolet wavelengths of light, Webb is designed to see mostly in infrared — this is because the light coming from the oldest, most distant parts of the universe is stretched out by their sources' acceleration away from us, placing it within the infrared spectrum.

Webb's mirror is also several times larger than Hubble's, enabling it to gather more light and see further in space and time. Because it’s collecting infrared light, which has a longer wavelength than visual or ultraviolet light, Webb needs a larger mirror to produce images that will be as sharp as those made by Hubble.

The Webb’s 18 gold-coated, beryllium mirror segments span a total diameter of 6.5 meters, compared with Hubble's 2.4 meter-wide glass mirror – but the Webb is far lighter, at just over half as much mass as Hubble.

Ultimately, Webb owes its mission to Hubble. The telescope will help astronomers answer the biggest questions we have about our universe — but Hubble's data enabled them to ask those questions in the first place.

Who is the James Webb Space Telescope named after?

James Webb with former President Harry Truman in 1961. Heritage Images/Hulton Archive/Getty Images

The James Webb Space Telescope is named after former NASA administrator James Webb, who ran the space agency from 1961 to 1968, during the heyday of the Apollo program.

Although Webb is best known for his role in managing NASA during the race to land astronauts on the Moon, he also insisted that the agency maintain a “balance,” in his words, between the high-profile goal of a Moon landing and other, less flashy, but scientifically important, missions. During the 1960s, NASA launched 75 missions to study the environment of space and observe distant stars.

Today, Webb is a controversial figure for his role in dismissing members of NASA on account of their sexuality as part of a U.S. government-wide effort known as the Lavender Scare.

How much does the James Webb Space Telescope cost?

The James Webb Space Telescope carries a total price tag of about $9.7 billion (or $10.8 billion, if you adjust for inflation). However, that cost has been spread out over the last 18 years – and the next 6 years.

From 2003 to this year, NASA has spent $8.8 billion on designing, testing, and building the space telescope. It will cost another $861 million to run the James Webb Space Telescope for the next 5.5 years.

That’s not counting the contributions from the European Space Agency, who are providing the launch vehicle and half of Webb’s four scientific instruments, to the tune of about $793 million, as well as the Canadian Space Agency, which has contributed about $156 million worth of instruments and sensors.

How long will the James Webb Telescope last?

The James Webb Telescope has taken decades to make, but it is designed to last at least 5.5 years once in space. NASA hopes to extend its mission beyond 10 years, though.

The telescope’s lifespan will depend on how long its instruments and support systems keep working correctly, as well as how long its thrusters can keep it in the right orbit.

The telescope will carry 10 years’ worth of thruster fuel, plus a bit extra in case of emergencies. But if an instrument breaks or an important system shuts down, Webb is too far away for a crewed repair mission like the ones that have helped maintain the Hubble. Once it is gone, there is really not much astronomers and astrophysicists can do other than keep their fingers crossed.

This piece has been updated to reflect a new launch time.

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