The James Webb Space Telescope, also known as the JWST, finally launched on December 25 for its journey 930,000 miles from Earth. This is the next generation that will replace the famous Hubble Space Telescope. Hubble has been capturing awesome photos for over 30 years, but it's time for something better. The JWST will be tasked with using its infrared sensors to explore some of the most distant and hard-to-see parts of the sky, helping with the search for exoplanets and with exploring the earliest days of the universe. So this seems like a good time to go over the most important scientific concepts that relate to space telescopes. Why Put a Telescope in Space? You can see all sorts of cool stuff, like nebulae and comets, from Earth with just some binoculars or a consumer telescope. But if you want research-quality images of distant galaxies, you have a problem: air. You might think air is transparent, but that’s only partially correct. Light is an electromagnetic wave, and it can have different wavelengths. People can only see a narrow range of wavelengths, from 380 nanometers (1 nm is 10-9 meter) to about 700. Our brains interpret the longer ones as red and the shorter ones as violet. These wavelengths are able to pass through the atmosphere without much of a decrease in brightness—so we can say the air is transparent to visible light. However, for other wavelengths of light that we can't detect with our eyes, the air is not so transparent. If we consider the infrared region of the electromagnetic spectrum (or wavelengths longer than red), then much of this light can be absorbed by both water vapor and carbon dioxide in the atmosphere. (Yes, this is the same thing that happens with global warming: When visible light hits the Earth’s surface, the temperature increases and it radiates infrared. Carbon dioxide in the air absorbs some of this infrared to further increase the atmosphere’s temperature. This can lead to bad things for humans.) This light absorption is also a particular problem for a ground-based infrared telescope. It would be like trying to look at the skies through clouds—it just wouldn’t work. One solution to this problem is to just put the telescope where there is no air: in space. (Of course, with every solution comes more challenges. In this case, you actually have to put a super-sensitive scientific instrument on a rocket and launch it, which is a bold move.) Why Does the JWST Look at Infrared Light? The JWST actually looks at two ranges of infrared light: the near infrared and mid-infrared. The near infrared is light with wavelengths very close to visible red light. It's the wavelength that your TV remote uses (if you can find it—it’s probably under the couch cushions). The mid-range infrared is often associated with heat, and that's mostly true. It turns out that everything produces light. Yes, you are sitting there making light. The wavelength of light that an object emits depends on its temperature. The hotter it gets, the shorter the wavelength of light. So, while you can’t see light emitted in the mid-infrared range, sometimes you can feel it.
The James Webb Space Telescope (Webb) will observe the Universe in the near-infrared and mid-infrared – at wavelengths longer than visible light. By viewing the Universe at infrared wavelengths with an unprecedented sensitivity Webb will open up a new window to the cosmos. With infrared wavelengths it can see the first stars and galaxies forming after the Big Bang. Its infrared vision also allows Webb to study stars and planetary systems forming inside thick clouds of gas and dust that are opaque to visible light. The primary goals of Webb are to study galaxy, star and planet formation in the Universe. To see the very first stars and galaxies that formed in the early Universe, we have to look deep into space to look back in time (because it takes light time to travel from there to here, the farther out we look, the further we look back in time). The Universe is expanding, and therefore the farther we look, the faster objects are moving away from us, redshifting the light. Redshift means that light that is emitted as ultraviolet or visible light is shifted more and more to redder wavelengths, into the near- and mid-infrared part of the electromagnetic spectrum for very high redshifts. Therefore, to study the earliest star and galaxy formation in the Universe, we have to observe infrared light and use a telescope and instruments optimised for this light like Webb. Star formation in the local universe takes place in the centres of dense, dusty clouds, obscured from our eyes at normal visible wavelengths. Near-infrared light, with its longer wavelength, is less hindered by the small dust particles, allowing near-infrared light to seep through the dust clouds. By observing the emitted near-infrared light we can penetrate the dust and see the processes leading to star and planet formation. Objects of about Earth's temperature emit most of their light at mid-infrared wavelengths. These temperatures are also found in dusty regions forming stars and planets, so with mid-infrared radiation we can see directly the glow of this slightly warm dust and study its distribution and properties. Webb is an international partnership between NASA, the European Space Agency (ESA) and the Canadian Space Agency (CSA).
The James Webb Space Telescope (JWST) is set to launch into orbit a whopping 930,000 miles (1.5 million kilometers) from Earth in 2018 [source: JWST]. It's set to observe some pretty spectacular science in the process: The JWST is designed to help us look far into the depths of the universe and help us understand the very early beginnings of galaxies, stars and planets. If you are up-to-date on your supersensitive telescopes, you might be frowning and harrumphing that Hubble already did that. Why the repeat? First off, life is short — let's not get all worked up about telescopes that haven't done us any harm. Second, NASA is quick to point out that JWST isn't just a replacement for Hubble; it's designed to look at space a little differently. Despite its similar mission to Hubble, JWST is equipped with some new technology and advancements that are going to let us probe a little deeper into the universe and collect images with more precision. The biggest change from Hubble? Instead of observing in the visible and ultraviolet spectrum, JWST will be performing almost all of its observations in infrared. Because infrared wavelengths are so obviously superior, right? Hmm. That doesn't check out. Why the heck does it matter that the Webb is looking at the infrared spectrum? There are several reasons that infrared is ideal for JWST, and each one fits nicely into some goals of the telescope's mission. For one, JWST is going to study nebulae — big, dusty clouds where stars are born. And while nebulae are gorgeous, scientists are not thrilled that they do a great job of obscuring the stars and the space around them. Infrared lets us look into those pretty clouds and get a better look at early star formation [source: Masetti]. Scientists also want JWST to get a good glimpse at some early galaxies. Here's one problem with "looking" at early galaxies: The farther back we look, the light that was once visible or ultraviolet has now become harder and harder to see by the time it has reached us. The light has now gone through a redshift and is only visible on the infrared spectrum. Got an infrared telescope? You can now see the first bright objects in the universe [source: Masetti]. One more infrared advantage: It can help us determine the atmospheres of exoplanets, our cosmic cousins that orbit other stars. JWST will be doing spectroscopy of those exoplanets by making detailed measurements of certain lights at different wavelengths or energies. Certain elements will give off different energies; by looking at the absorption spectrum, you can see what molecules are present in the atmosphere. Infrared can show a larger number of spectral features than can visible or UV wavelengths [source: Masetti]. Page 2
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Why does the jwst observe infrared light, and what are the scientific advantages for astronomers?
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