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Compare Webb's Images to Hubble

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Re: Compare Webb's Images to Hubble

#201

Post by sushibowl »

dotancohen wrote: post #173
bryananderson wrote: post #124

Earlier quoted context omitted.

Seeing through dust is part of it. Another part is redshift: because of relativity, things moving away from us appear redder (longer wavelength) the faster they’re moving away. That’s the same principle (Doppler effect) as the lower-pitched siren sound as the ambulance drives away. Because the universe itself is expanding, the farther something is from us, the faster it’s moving away relative to us, and the more reds…

Your statements about redshift and distance are correct, but I do not see where relativity comes into it. Even in Newtonian physics redshift occurs. If you could elaborate I would love to learn. Thank you!

Newtonian physics does have the Doppler effect which can cause red shift, but it doesn't accurately explain the red shift that occurs when observing distant galaxies. That's because this red shift occurs due to three factors:

1) The galaxy is moving away from us. This is most like the classic Doppler effect, but because of the high relative velocities involved, time dilation needs to be taken into account to model the red shift accurately, thus at least special relativity should be used.

2) The light travels through space with different curvature. For example, light originating near a very massive star will red shift when moving away from that star because it moves into less curved space. General relativity is needed to explain this effect.

3) The light travels through expanding space. For very distant galaxies this becomes the dominating factor of red shift, as we see an amount of red shift directly corresponding to their distance from earth. General relativity also explains this effect.

Re: Compare Webb's Images to Hubble

#202

Post by MeteorMarc »

ygra wrote: post #193
AQXt wrote: post #191

Earlier quoted context omitted.

> especially since the images are stylized / colored anyway The thing that I don't like about the new images is the abuse of star flare effect. The colors are okay, but the flares... that's simply too much.

It's not an effect. It's a diffraction artifact that's a consequence of the telescope construction. Explained here for example: https://bigthink.com/starts-with-a-bang/james-webb-spikes/

Although this reference nicely explains the origin of the diffraction pattern on the JWT images, it does not explain why the spikes seems to extend much farther then in the Hubble images. My hunge is that the JWT succeeds much better to gather all the light into a real point which makes the primary diffraction pattern stronger too.

While this is very important for scientific work (easier to see planets!) it is less appealing to the eye. Also note that some JWT images have some faint blue streaks which in effect are diffraction spikes from bright stars outside the field of view.

Re: Compare Webb's Images to Hubble

#203

Post by nullc »

noisy_boy wrote: post #156
mholt wrote: post #4

Here's a backyard telescope versus Webb: https://twitter.com/AJamesMcCarthy/status/154694183270093209... More comparisons on Twitter, some zoomed in: - https://twitter.com/Batsuto_/status/1546899241880240128 - https://twitter.com/Batsuto_/status/1546900387931766784 - https://twitter.com/JBWillcox/status/1546881033597075457 - https://twitter.com/jason4short/status/1546626672488632321 I'm not a physicist, so I've only…

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).

Re: Compare Webb's Images to Hubble

#204

Post by dtgriscom »

Cthulhu_ wrote: post #182
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…

If I may get political here (nothing personal / no direct reply to the parent comment): > stunning images was enough to get the public to support a $10B project. I don't believe public support is relevant; is there public support for the >$700B a year spent on the military?

Public support for NASA drives the members of Congress to allocate funds for its work. So, NASA spends a whole lot of effort showing the public how cool its work is. That, and it divides its facilities and subcontractors across the various states to ensure that every member of congress has constituents who benefit from its payroll.

Re: Compare Webb's Images to Hubble

#206

Post by sandgiant »

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?

The JWST is only now entering science operations. What you see is pretty pictures taken as part of the commissioning and PR efforts of NASA.

The actual science is yet to come, but will likely not look as spectacular to the layperson.

Edit: Here is an overview of the science that JWST is going to be doing in Cycle 1: https://www.stsci.edu/jwst/science-execution/approved-progra....

Re: Compare Webb's Images to Hubble

#207

Post by sandgiant »

justanotherme wrote: post #178

A question to the experts here: What will be the most exciting things to be explored within the next months? What insight could come out of it, which open questions could be answered? Hints to life on other planets by observing specific spectrums of specific ones? Could certain open questions about the early universe be decided? Or something else?

What you find most exciting is a subjective thing. I don't have a clear answer, but you can browse through the list of accepted proposals in cycle 1 and decide for yourself: https://www.stsci.edu/jwst/science-execution/approved-progra....

Re: Compare Webb's Images to Hubble

#208

Post by dtgriscom »

Unklejoe wrote: post #143

I read at some point that a piece of dust hit the telescope and potentially damaged it. I'm guessing that it turned out not to be a big deal or maybe they were able to work around it? Does anyone have any insight? The fact that they're releasing good pictures and not mentioning it seems like a good sign to me. Searching for this stuff is kind of hard (information overload), so I'm wondering if anyone here has more up…

https://blogs.nasa.gov/webb/2022/06/08/webb-engineered-to-en...

Summary: they can see it in the data, but events such as this were expected and part of the lifetime of the telescope.

Re: Compare Webb's Images to Hubble

#210

Post by 9991 »

arjvik wrote: post #189
jhugo wrote: post #185

Earlier quoted context omitted.

Looked like from what perspective? A human eye on Earth?

OP clearly means from an observer moving at (approximately) the same velocity as the object emitting the light.

The objects aren’t really moving in that sense. The expansion of space over time is what stretches the light.
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