Answering the most popular questions about the James Webb Space Telescope

 The whole world is waiting for the launch of the new observatory, the James Webb Space Telescope (or JWST). This 6.5 meter infrared telescope will look deeper into space and further back in time than any other observatory. 

But…we might have to wait a little bit longer to see the mission take off. Earlier this month NASA officials confirmed that, because of the coronavirus, the launch, that was planned for March 2021, will be delayed. Hopefully, not for long.

While we are waiting for the new launch date announcement, let’s learn more about “the most powerful space telescope ever built”! Today we will answer the most popular questions about the Webb Telescope we get asked during the Planetarium Shows for groups

For more information about the space observatory see our blog post Webb Telescope to unravel the mystery of brown dwarfs.


Why do they call it the Webb telescope? Is Webb telescope the same as the Web (WWW)?

The James Webb Space Telescope, formerly the Next Generation Space Telescope, was named after the second NASA Administrator James Edwin Webb. James E. Webb was head of NASA from 1961 to 1968 and left the post just before the first manned Apollo flight (Apollo 7). Under his direction, NASA launched the first astronauts into orbit and the first robots to the Moon, Mars and Venus. Webb was a great supporter of space science research. 


Why do we need to send JWST into Space? Why cannot we just observe from the ground?

Our post Do we really need to put telescopes into Space? will give you the detailed answer to this question. 

To sum it up, we need to send telescopes up into space because here on Earth we observe through the atmosphere. Some wavelengths pass through the air practically undisturbed. But others get blocked. The Webb Telescope will be most sensitive to the near and middle infrared light. Unfortunately, the Earth’s atmosphere is mostly opaque to the infrared. Therefore it is absolutely necessary to “lift” the instrument above the atmosphere to be able to “see”.


What kind of radiation will JWST detect and what will we “see” in that light?

Human eye can only see a tiny portion of the electromagnetic spectrum, i.e.  waves of certain lengths, from violet (shortest visible wavelengths) to red (longest visible wavelengths). Waves that are shorter than violet are called ultraviolet (followed by X-rays and Gamma-rays). Waves that are longer than red are called infrared (followed by radio waves). We cannot see infrared light, but can feel it as heat.

JWST will cover wavelengths from 0.6 to 28.5 microns (1 micron, or micrometer, is 106m).

That means the observatory will “see” some visible light, namely yellow-to red part of the rainbow (0.56-0.7 micrometers), near-infrared light (0.7-5 micrometers) and mid-infrared light (5-30 micrometers). 

The telescope’s sensitivity to the infrared light will allow scientists to study

  • Stars and planets as they form and black holes in the centers of galaxies 

Regions of star formation as well as central black holes in galaxies are enveloped in gas and dust. This dust blocks visible light, but lets the infrared radiation through!

  • First galaxies

The Universe is expanding, so when we look further into space, we look further back in time. The most far-away galaxies, therefore, are the early galaxies that were formed soon after the Big Bang. Unfortunately, we cannot see them with optical telescopes. As visible light from these galaxies travels to the Earth, it gets stretched, or redshifted. So what started as ultraviolet or visible light becomes infrared light. That’s why we need a very powerful infrared telescope, such as the James Webb Space Telescope! 

  • Exoplanets

JWST will look for planets around other stars and study already known exoplanets in greater detail. The observatory will be able to analyze the light from the stars as it passes through their planet’s atmosphere, and, as a result, to tell astronomers what these atmospheres are made of! Who knows, maybe the telescope will even spot another planet capable of supporting life!


Why is JWST so far away from the Earth?

Unlike the Hubble Space Telescope, which is in the Low Earth Orbit, JWST will be orbiting the Sun. It will be placed near* a very special point in the Earth-Sun system, called L2. 

L2, or the second Lagrange point, of the Earth-Sun system lies on the opposite side from the Earth than the Sun at a distance of about 1 million miles from our planet (to compare, Hubble is only 340 miles away). 

Many spacecraft use this unique position by because it gives a great view of the outer space and allows for continuous communication with the Earth. Also, in this position JWST will be able to block the radiation from the Sun, the Earth and the Moon with one giant heat shield as the three bodies will be in the same direction. That (and the great distance, of course) will prevent the telescope from warming up and, consequently, from polluting the observations with its own infrared radiation. 

*We want to stress that the telescope will be placed not in L2, but in orbit AROUND L2. 


Why is the telescope’s big mirror foldable? 

A mirror (or a lens) is an eye of a telescope. The bigger the mirror, the more light it can collect and therefore the fainter objects we can see. 

JWST will study objects that are very far away and therefore are very faint. To see them, it will need a big eye. It was determined that a mirror 6.5 meter in diameter will be required to carry out the research planned for JWST.

But there is simply not enough space inside a rocket to fit a telescope that big. Also, big mirrors are extremely heavy, very difficult to make and don’t hold shape very well. The solution to these problems is to make a telescope of smaller lighter segments, fold it for launch and then deploy in orbit! That’s the general idea behind the JWST design!


Why does the James Webb Telescope look like a honeycomb? Is it made of real gold?

1. The primary mirror of the James Webb Telescope indeed looks like a honeycomb. This is because it is made of 18 hexagon-shaped panels. But why hexagons?

In mathematics this is known as tiling problem (or tessellation problem). The tiling problem asks us to cover a surface with shapes so that there are no gaps or overlaps.

In our case cover will mean replace and the surface we want to make out of segments/tiles is the round mirror 6.5 meter in diameter. Of course, we would prefer the tiles to be the same shape as they would be easier to manufacture. Also, we don’t want any gaps between the tiles and we need the resulting tessellation to be highly symmetrical. Otherwise the images our mirror will create will be distorted. In other words, we need a regular tessellation!

Turns out there are only three regular shapes that can do the job: triangle, square and hexagon.

The panels of the JWST primary mirror are hexagons (and not triangles or squares) because the overall shape they create is the closest to round. And they might be easier to make.


2. The signature “golden honeycomb” is actually made of light and strong material, called beryllium. Beryllium is coated in gold which, in turn, is coated in glass to protect the golden surface from scratching (gold is very soft). The layer of gold is very thin,  100 x 10-9 meters. Gold is excellent at reflecting infrared light, much better than other materials traditionally used in telescopes, such as aluminium. That is very important, because the more light bounces off the surface of the mirror, the better signal we will receive and the less noise (that is absorbed and reradiated light) the telescope itself will produce.


What type of telescope is JWST?

The answer depends on what characteristics (such as location, wavelength, design) we want to base our classification on. 

 On location:

  • space telescope (will observe from orbit, not from the surface of the Earth)

On Wavelength:

  • infrared telescope (will detect infrared light)

On Design:

  • reflector (that means uses mirrors, not lenses) or, more specifically, Cassegrain reflector (in this design when the light bounces off the secondary mirror, it goes back through the hole in the primary mirror)
  • three-mirror anastigmat, or Korsch telescope (that means it’s optical system consists of three gold-coated mirrors that are curved to minimize image distortion; these mirrors are:

-Primary concave mirror D 6.5m (the honeycomb) 

-Secondary convex mirror D 0.74m (single mirror on the “tripod structure” above the main mirror)

-Tertiary mirror (sits inside the black structure in the centre of the honeycomb)


Who will get to choose what JWST will study and how will the telescope know where those objects are? What will be the Webb’s very first target?

When a telescope is used for the first time, it is called “first light”. The goal of this first viewing is not to do scientific observations, but to test the instrument and make sure everything is working correctly. Only after JWST is tested, the observations will begin. The first thing the telescope will need to do is to precisely align the 18 segments of its primary mirror. To do this, an image of a star will be taken separately with every one of the segments, and then their positions will be adjusted!


Once the telescope is ready for observations, the science will begin. 

Some of the telescope’s time will be reserved for the researchers who helped to develop the telescope. Some will be allocated at the Director’s (of Space Telescope Science Institute) discretion. Over 80% of time will be available to the astronomers from all over the world. To observe with JWST, scientists will need to submit proposals and explain what they want JWST to look at, where these objects are, why it is important, and why it cannot be done with another telescope. These proposals will then be reviewed and the best will be chosen as JWST’s targets. 


The telescope will use its many sensors to determine its whereabouts and to make sure it is pointed at the right target. Its Sun sensors will tell how the observatory is oriented in relation to the Sun. The star trackers (two small telescopes with wide fields of view) will see a bigger patch of the sky that is easier to identify (similar to how we zoom out of google map to check what area we are looking at). And as the telescope is turning from target to another, its gyroscopes (JWST has 6 of them!) will tell how fast the observatory is rotating and in what direction.


If one of JWST’s instruments stops working, will astronauts be able to go there and repair the telescope, like they did with Hubble? 

Unfortunately not. The telescope will be about 4 times further away from the Earth than the Moon.That is (at the moment) well out of reach of any potential servicing mission. 

The mission is expected to last between 5 and 10 years. Eventually, even if all the instruments work correctly, the observatory will run out of fuel it needs to stay in orbit around L2.

Are there any visual resources to help me better understand things about the James Webb telescope and its mission?

Absolutely! On NASA website you will find lots of photos and videos that cover every aspect of JWST’s mission.  Here are some hands-on activities you might also like

  • WonderDome presenters in infrared

  • Make your own James Webb Telescope deployment flipbook
  • See in infrared! Infrared cameras, like the one in the National Space Centre, will allow you to see yourself in infrared light. That’s the kind of light JWST will be able to detect.
  • Make your own James Webb Telescope paper model
  • Print out this Electromagnetic Spectrum Poster. It will help you to get familiar with different regions of the EM spectrum and memorize their respective wavelengths/ frequencies. 
  • Visit our Portable Planetarium session on  robotic space exploration and see the James Webb Telescope, Curiosity Mars rover and many other science missions! A the end of the show our Star Dome presenters will be happy to answer your questions!