Huge. This is the first large telescope observing in far infrared. Some things:

- very early galaxies (so far that they are redshifted to far IR). Hence the “looking into the start of the Universe” talk). We know they are there, and that they are unusual and super-interesting, but just can’t see them.

I think this is high on the agenda so I’m guessing some PR shots of ancient galaxies are due.

- cold objects nearby; brown dwarves, rogue planets etc. Maybe planets around nearby stars.

- I haven’t seen this discussed, but maybe: Kuiper Belt objects, maybe looking for Planet X etc.

Even earlier than galaxies, we'll be able to see some of the first stars that existed before galaxies formed.

IIRC the telescope will be able to see "back" into 98% of the observable universe.

Yup! If the universe's age were a single year, we're looking back to January 6th. Truly remarkable. :)

what prevents us from seeing back any further?

Disclaimer: not a cosmologist. We can see back further with other instruments, just there's less to see.

The universe's history: https://en.wikipedia.org/wiki/Chronology_of_the_universe#/me...

- We can see the cosmic microwave background (CMB), the earliest photons after the big bang still observable. This is ~14 minutes into Jan 1 if the whole age of the universe is a year. Satellites like the WMAP have done a great job of that.

- The dark ages that follow had few photon sources.

- JWST will be observing the earliest stars following that era.

There's a proposed radio telescope (that would have to be on the far side of the moon!) to observe neutral hydrogen photon emissions from the dark ages: https://en.wikipedia.org/wiki/Dark_Ages_Radio_Explorer

There were maybe 100 million years after the big bang with no star formation. Darkness. Here's a page about that era as it relates to Webb: https://webb.nasa.gov/content/science/firstLight.html

Redshift and mirror diameter. There is very little old light, so to see further, you have to collect more light to have a chance of catching those ancient photons. Also, due to expansion of space, the older the photon, the less energy it has, so you have to look deeper and deeper into infrared.

> what prevents us from seeing back any further?

The other comment mentioning darkness is wrong.

In the very early universe, it was extremely bright and hot. It was only after 100,000 years or so the universe cooled down enough to become transparent.

One of the more interesting things that we'll get is data about what's in the atmosphere of exoplanets

https://jwst.nasa.gov/content/science/origins.html

Note that the next 5 months or so will consist of mirror cooling and calibration, so nothing until summer.

This one was really interesting to me because this kind of observation didn't exist when JWST was being specced out. We didn't know there were that many exoplanets around that we'd want to look at.

Would you happen to know if they can make intermediate observations while this is in process e.g. observe a relatively nearby object before the telescope is fully cooled and aligned? I'm wondering if they would be able to prove out the optics early on - this is no slam dunk as the Hubble proved.

Not really… these telescopes aren’t like snapping a photo, they take long exposures. The famous hubble deep field image was a 20+ day exposure time spread out over months (due to orbits, etc).

Trying to get an image out of it too early would just be a mess, it’s kind of an all or nothing affair. The sensor needs to be at the right temperature and the mirrors need to be precisely aligned. It’s all built to be outrageously sensitive so it can operate at the level it’s meant to.

Also, each image it’s scheduled to take has been submitted years in advance.

My knowledge is basically 0, but from what I understood the sensitivity of the sensor is so high, that anything above its operational temperature would overload it and basically make a 'white' image. Basically like having a kitchen scale and then trying to weight an elephant on it (and somehow not breaking the scale in the process).

This will only work for a handful of very nearby exoplanets, unfortunately.

hell I’d be excited for 1!

The planets around Alpha Centauri orbit a red dwarf. They are almost certainly tidally locked and lack any atmosphere. The more distant ones that might not be tidally locked are likely frozen like Pluto.

...but who knows.

It will take another 6 months before JWST will go into operation it seems. This page has a list of approved programs.

https://www.stsci.edu/jwst/science-execution/approved-progra...

Apparently it takes about 100 days for the instruments to cool down far enough.

https://planet4589.org/space/misc/webb/time.html

"Meet hot methane-breathing life forms in your neighborhood!"

"5pc from Coatesville, PA"

The full list of the first set of scientific missions is available here: https://www.stsci.edu/jwst/science-execution/approved-progra...

The overall idea is that JWST can see very faint objects in the infrared spectrum. The analogy I've heard is that it could pick out a bedroom nightlight on the moon from earth.

Being able to see how galaxies evolved - you can see a galaxy 200M light years after the Big Bang and compare it to Hubble’s 500M years after the Big Bang.

Also spectra will be available to understand physical and chemical compositions at early times.

I'm excited to see what we learn about the earliest days of the universe since it can observe highly red-shifted objects.

“Images of the first galaxies, the first black holes” iirc from Smarter Everyday’s interview with John Mather, sorry don’t have a time code for you

https://youtu.be/4P8fKd0IVOs

Word on corners of the interwebz has it that this is gonna prove the existence of aliens (or at least gov. are gonna frame JW as the indicator of alien life)

It could find a candidate biosphere. If we see a lot of free oxygen or other super reactive things like fluorine that would be very suggestive. It’s not proof but we don’t know many other processes that can maintain a high percentage of oxidizers in an atmosphere.

If we saw that the next step would probably be a telescope designed specifically to observe that target. There are some thoughts about using a telescope out near Pluto that could use the sun as a gigantic gravitational lens to photograph an exoplanet and get very detailed spectroscopic information.

If we have a planet nine that is a primordial black hole that would be an absolute killer gravitational lens.