SmarterEveryDay did a good video on it ELI5: the universe is expanding. the expansion means that the light from very distant objects is redshifted. the farther away something is, the bigger the...
the universe is expanding. the expansion means that the light from very distant objects is redshifted. the farther away something is, the bigger the shift is.
for extremely distant objects, some of them more than 10 billion light-years away, most or all of the observable light from them has been redshifted into the infrared spectrum.
observing in the infrared using ground-based telescopes is very difficult, because of how strongly the atmosphere absorbs infrared radiation.
so you really want a space-based telescope. but not just any space-based telescope. the Hubble had infrared instruments, for example, but they were limited in their accuracy because the telescope itself emits infrared radiation (as does anything warmer than absolute zero). it's a bit like taking a picture of a distant object vs taking that same picture but with a bright light bulb in the foreground.
so to make the most accurate infrared telescope possible, you need to cool it way down. the Webb is kept at 50 degrees Kelvin / -223 Celsius / -370 Fahrenheit to minimize the infrared radiation the telescope itself puts out.
the massive sunshield (they say tennis court sized but I don't think that conveys the scale - look at this picture of it with people standing next to it), is crucial to that. so is its orbit, at the Earth-Sun L2 Lagrange point. in that orbit, from the Webb's perspective, the Earth and the Sun will always be in the same part of the sky, year-round, so it can position its sunshield to block heat from both of them.
all this work into accuracy, and specifically in the infrared spectrum, means we'll be able to look at extremely far away objects, which corresponds to very far back in time. the farthest away / oldest galaxy we've observed, for example, GN-z11, existed about 400 million years after the Big Bang. there was lots of interesting stuff happening in the early universe around that time, and Webb will let us study it in a way that's never been possible before.
Astronomer here! What an amazing Christmas present for anyone who loves space!!!
took the liberty of writing a few notes down, because while I know some of you know every nuance of James Webb Space Telescope (JWST), many more people have the same general questions. So, with that…
What is JWST and how does it compare to Hubble? JWST is the long-awaited successor to the Hubble Space Telescope, which launched in the early 1990s and revolutionized astronomy in a Nobel-prizewinning way. However, we have many new frontiers in astronomy Hubble is not able to probe, from finding the first stars to details about exoplanets, and JWST is poised to do that! First of all, it is just plain bigger- the mirror size is what is key in astronomy, and Hubble’s is 8 feet across (2.4m), but JWST’s is ~21 feet (6.5m) across! In terms of sheer bulk, Hubble is about the size of a bus, but JWST is the size of a tennis court (due to a giant sun shield)- this truly is the next generation's telescope!
Second, the light itself JWST will see is literally different than Hubble. Hubble is basically set up to see the light our eyes does, but JWST is going to see only the orange/red light your eyes see, and the infrared light beyond red that you don't see. Why? Because the further you peer into space, the more "redshifted" the light becomes, aka what is normal light to us emitted billions of years ago now appears in infrared. So, if you want to look to the furthest reaches of the universe, that's where you've gotta look.
Finally, JWST is not orbiting Earth like Hubble, but instead will be outside Earth's orbit farther than the distance to the moon from us, at a special point called L2. This was chosen because there are several advantages to it- the infrared instruments on JWST need to be kept very cold, beyond levels what even the environment around Earth can get to. As an added side bonus to astronomers, JWST is not limited to observing only ~half its time like Hubble is (due to being in the sun half the time in its orbit), and thanks to having a sun shield we almost get 24 hours a day to observe! There are definite disadvantages though- JWST is currently only built to last ~10 years because it's limited by the amount of fuel on it (Hubble, OTOH, has stayed in orbit thanks to multiple missions by astronauts from the space shuttle days to fix/upgrade it). The good news is being able to upgrade JWST in ~10 years when needed (most likely via robotics) was listed by various NASA admins as a top priority... so let's keep clamoring they follow through on supporting their investment!
What new science can we expect? NASA (and the ESA and Canada, also big partners in JWST costs) don't just spend billions of dollars on a next generation space telescope without damn good plans on why it's needed, and in fact for JWST there are key science goals outlined already. They are:
To study light from the first stars and galaxies after the Big Bang
To study the formation and evolution of said galaxies
To understand the formation of stars and planetary systems
To study planetary systems and the origins of life.
Those are all revolutionary goals in themselves, but that said, it's important to note that whenever you get an instrument like this that's just leagues ahead of anything there's been before, you will make new discoveries no one expected because the universe is just so amazing beyond our wildest imaginations (it happens every time, and is one of the most incredible things about astronomy IMO). For one example, do you know why it was called the Hubble Space Telescope? Because it was built to measure the Hubble constant, which drives the expansion of the universe. But incidentally along the way Hubble was used to discover dark energy, the Hubble Deep Field, and just revolutionize astronomy in many ways, all while creating beautiful images for all the world for free. There's so much to uncover, and we don't even know it all yet!
To give you an idea, those key science goals were outlined many years ago by astronomers, and the research group I'm in got JWST time... to follow up on a neutron star merger if one meets our specific criteria in the first year of science operations. (I'm not in charge of this data myself, but you can bet I'll be looking over the shoulder of my colleague as it comes in!) Seeing as we have only ever literally seen one of these mergers in actual detail before (with LIGO/Hubble- JWST can detect them to much greater distances), I know those results will be incredible!
Enough talk- when are we getting the first pictures?! Probably about six months, I'm sorry to say, because a ton of work still has to happen. First the telescope has to travel to the L2 point and unfurl into its giant size from its rocket casing size, which is going to take several weeks and is rather anxiety-inducing to discuss in detail on my Christmas holiday, so let's not. This is going to take about a month. Then you need to do things like align the mirror properly (its famous 18 segments gotta be perfectly fit together, and it's a super slow process) and then you have to make sure the instruments actually focus- another 4 months. Finally, there are a small number of "easy science" commissioning targets to put the instruments through their paces, and those are going to give you the first images. I promise, they'll be front page on every geek and non-geek news outlet on Earth when they're out, so you won't miss it. They will be better than Hubble's, no doubt, and converted on the computer to take into account the infrared light over optical (sorry to report if you hadn't heard before, but all pretty Hubble images were heavily post-processed too).
And then, the real fun begins- Cycle 1! Last year JWST had its first open call for science proposals, where literally anyone on Earth can propose a project for JWST to do- you just need to make a good enough case to convince a panel of astronomers that you deserve that precious telescope time. Those projects are already approved, and you can read all about them here! I'm incredibly excited to see how this first science cycle goes, both in my group's research but also to see what my talented colleagues who got time will do with it!
This has gone on long enough, but to wrap up... it's very surreal for me to see JWST launch (I wasn't expecting how nervous I got even compared to other launches). I became interested in astronomy at age 13, circa 2000, so it's no joke to say over half my life has been waiting for JWST to launch (why it's taken so long is subject to another post sometime). It's such a personal and professional milestone for me to see it happen! And for all the 13 year olds out there getting interested in astronomy now thanks to JWST (and older)- wow, do we have a lot of exciting discoveries in store in the coming years! And maybe someday you'll get time of your own on JWST- as I said, anyone on Earth can potentially do it if you study hard enough!
TL;DR Today is historic because JWST is going to revolutionize astronomy, no hype in saying that, but it's gonna be a little while until the first pictures come through yet
SmarterEveryDay did a good video on it
ELI5:
the universe is expanding. the expansion means that the light from very distant objects is redshifted. the farther away something is, the bigger the shift is.
for extremely distant objects, some of them more than 10 billion light-years away, most or all of the observable light from them has been redshifted into the infrared spectrum.
observing in the infrared using ground-based telescopes is very difficult, because of how strongly the atmosphere absorbs infrared radiation.
so you really want a space-based telescope. but not just any space-based telescope. the Hubble had infrared instruments, for example, but they were limited in their accuracy because the telescope itself emits infrared radiation (as does anything warmer than absolute zero). it's a bit like taking a picture of a distant object vs taking that same picture but with a bright light bulb in the foreground.
so to make the most accurate infrared telescope possible, you need to cool it way down. the Webb is kept at 50 degrees Kelvin / -223 Celsius / -370 Fahrenheit to minimize the infrared radiation the telescope itself puts out.
the massive sunshield (they say tennis court sized but I don't think that conveys the scale - look at this picture of it with people standing next to it), is crucial to that. so is its orbit, at the Earth-Sun L2 Lagrange point. in that orbit, from the Webb's perspective, the Earth and the Sun will always be in the same part of the sky, year-round, so it can position its sunshield to block heat from both of them.
all this work into accuracy, and specifically in the infrared spectrum, means we'll be able to look at extremely far away objects, which corresponds to very far back in time. the farthest away / oldest galaxy we've observed, for example, GN-z11, existed about 400 million years after the Big Bang. there was lots of interesting stuff happening in the early universe around that time, and Webb will let us study it in a way that's never been possible before.
From Reddit: