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Compare Webb's Images to Hubble

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Re: Compare Webb's Images to Hubble

#241

Post by credit_guy »

supernova87a wrote: post #213
rkagerer wrote: post #174

Earlier quoted context omitted.

Didn't the observed light shift into IR wavelengths due to the expansion of space over the last billions of years while it traveled to us? Do the recolored images have any relation to what the original view would have looked like, or is it just arbitrary "artistic license"?

Hey, that's an interesting and uncommon question that I had not seen elsewhere -- They did not release or talk in much technical detail of how the images were assembled, which I'm sure will be done at some point. I do not think the colors do correspond (at least not deliberately), for 2 reasons: First is that the image of the Deep Field ("SMACS") contains galaxies at a range of redshifts. For example there may be gal…

A tangential question. If these galaxies are so much redshifted, then they are probably very, very far. Like more than 1 billion ly far. And if that is so, they should look exactly the same today, tomorrow, in one year, or in a hundred years. If for some reason we wanted these images in much higher resolution, could we just point the camera to the same spot and take millions of shots and then apply a super-resolution algorithm?

Re: Compare Webb's Images to Hubble

#242

Post by supernova87a »

credit_guy wrote: post #241
supernova87a wrote: post #213

Earlier quoted context omitted.

Hey, that's an interesting and uncommon question that I had not seen elsewhere -- They did not release or talk in much technical detail of how the images were assembled, which I'm sure will be done at some point. I do not think the colors do correspond (at least not deliberately), for 2 reasons: First is that the image of the Deep Field ("SMACS") contains galaxies at a range of redshifts. For example there may be gal…

A tangential question. If these galaxies are so much redshifted, then they are probably very, very far. Like more than 1 billion ly far. And if that is so, they should look exactly the same today, tomorrow, in one year, or in a hundred years. If for some reason we wanted these images in much higher resolution, could we just point the camera to the same spot and take millions of shots and then apply a super-resolution…

I believe that in the image assembly pipelines for processing these astronomical images, they already do take into account / use the "dithering" patterns that you're hinting at. (Often the telescope will be pointed in a pattern with sub-pixel offsets over multiple exposures to do exactly this).

However, 2 factors:

1) there is an intrinsic limit I believe to how much more resolution you can recover (maybe a factor of approx. 2x?), for a lot more exposure time needed However, also at these faint levels of brightness you're also competing against intrinsic photon and sensor noise)

2) practically, given the value of the telescope's time and not much more to be gained (science-wise) from achieving this next order of spatial resolution, they want to spend the time on other new targets instead of sitting on the same patch for much more time.

(you can even try this at home: https://petapixel.com/2015/02/21/a-practical-guide-to-creati... )

Re: Compare Webb's Images to Hubble

#244

Post by iampivot »

supernova87a wrote: post #97
nacogo wrote: post #74

Earlier quoted context omitted.

Agreed! In the SMACS 0723 image, there is a red spiral galaxy near the top right which is effectively not present in the HST image because it was redshifted out of the spectrum. This implies it's one of the galaxies receding the fastest from us in the image right? And therefore also among the oldest and farthest away? https://blog.wolfd.me/hubble-jwst/

Yes, well 2 possible effects: 1) as you said, its flux is predominantly in the IR 2) it could have been fainter than the sensitivity of the HST instruments but now seen because of the sensitivity of JWST But given that it appears so bright in the JWST image similar to other nearby galaxies that do appear in the HST image, your bet on #1 seems reasonable. Also there is another point: rather than a highly redshifted ga…

Isn't one way to detect redshift to check if there's absorption of certain frequencies due to the light passing through matter on the way here? The absorption will be redshifted as well?

Re: Compare Webb's Images to Hubble

#245

Post by lm28469 »

bastardoperator wrote: post #90

Downvote me to hell, but as a person who has zero understanding of what differentiates Hubble from Webb, the pictures alone just aren't doing it for me. I was excited to see something completely new given 30 years and 10 billion dollars and instead I feel like I'm seeing what looks like an enterprise upgrade and feel slightly disappointed. What am I missing?

> What am I missing?

Several PhD in astrophysics.

They didn't spend 30 years and 10B for a big jpeg don't worry

These pics are gimmicks sent to the public as a "see what we did". It's like if Armstrong personally brought you back a moon rock, you'd be like "yeah cool that's a rock" because you don't have the instruments to analyse it nor the knowledge to know what to even look for.

Re: Compare Webb's Images to Hubble

#246

Post by noisy_boy »

nullc wrote: post #203
noisy_boy wrote: post #156

Earlier quoted context omitted.

Which begs the question: is there a computational way to "collapse" the spikes in post-process? They are beautiful but also sort of distracting when you are trying to take in the enormous mass of stars in these photos.

deconvolution, but it's more art than science because the problem is ill conditioned and blows up without regularization-- particularly if any part of the spike is overexposed (which it usually as you only notice the spikes on extremely bright stars).

Hmm - maybe a use case for (trained?) machine learning? I don't have much idea about ML so not sure if it makes any sense.

Re: Compare Webb's Images to Hubble

#248

Post by supernova87a »

nabla9 wrote: post #187
supernova87a wrote: post #61

For the professional (or former professional) astronomers among us, I will make my somewhat amused observation that what people are most paying attention to is not really the distinguishing features of JWST. People seem most impressed by the apparent increase in resolution of the images, which is not from a certain point of view the hardest thing to do . HST might have done that if its instruments had been of differe…

>The new thing is observations in the IR, Not a new thing. Herschel space observatory operated in same location (L2-point) as JWST and it was IR telescope. https://www.google.com/search?q=Herschel+space+observatory+i... Mirror sizes: Hubble 4.0 m2 (43 sq ft) Herschel 9.6 m2 (103 sq ft) JWST 25.4 m2 (273 sq ft) Hubble had ~40% of the Herschel's collecting area and Herchel had 40% of the JWST's collecting area.

That is a good point -- my simplification of the advance provided by JWST is aimed at saying, JWST is kind of the first major telescope with such depth and resolution to complement the deep fields of HST that everyone is so familiar with.

Herschel, while impressive also, was far-IR (if I recall) and much lower resolution, which was good for certain research areas, but less complementary to the HST deep fields for the, well, currently fashionable, recent study of galaxies at high redshift.

Re: Compare Webb's Images to Hubble

#250

Post by Balgair »

tonymet wrote: post #247
Balgair wrote: post #243

Earlier quoted context omitted.

I mean, it's pretty much asking what the practical applications of astronomy are. It's the marquee instrument now.

feel free to share your thoughts

seems pretty cool, lots of tech n stuff.

How about you?

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