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Compare Webb's Images to Hubble

johnedchristensen.github.io

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Re: Compare Webb's Images to Hubble

#91
post #26

Question for anyone who happens to be an expert: Is there any way to quantify how much better Webb is independently of the amount of time used to take the exposures? Like, could Hubble achieve the same quality of images as Webb if it was given 100x (or whatever) more time exposure? I'm trying to understand how much the improvement is "speed of convergence" vs. "quality of asymptotic result". (Though... is that even a…

I'm no expert either, but I imagine that high exposure times come with more motion blur. So just cranking up exposure time does not necessarily result in better pictures.

There's effectively no motion blur visible.

The most pronounced effects might be paralax of nearby stars to thousands of light-years at the outside. That would be observable in images taken at opposite sides of Earth's orbit around the Sun, a baseline of about 300 million km (186 million miles). Even that will be phenomenally small, too small to be observable for most objects within our own galaxy (the Milky Way) let alone the distant objects JWST is most concerned with.

From Wikipedia:

In 1989 the satellite Hipparcos was launched primarily for obtaining parallaxes and proper motions of nearby stars, increasing the number of stellar parallaxes measured to milliarcsecond accuracy a thousandfold. Even so, Hipparcos is only able to measure parallax angles for stars up to about 1,600 light-years away, a little more than one percent of the diameter of the Milky Way Galaxy.

The Hubble telescope WFC3 now has a precision of 20 to 40 microarcseconds, enabling reliable distance measurements up to 3,066 parsecs (10,000 ly) for a small number of stars.[10] This gives more accuracy to the cosmic distance ladder and improves the knowledge of distances in the Universe, based on the dimensions of the Earth's orbit.

https://en.wikipedia.org/wiki/Stellar_parallax

JWST's optical acuity is roughly similar to Hubble --- despite the larger mirror surface, it's using longer wavelengths of electromagnetic radiation, with lower resolving power.

Movement of the JWST itself is kept to an absolute minimum for obvious reasons. It would simply be unusable as a telescope if this weren't the case.

Absolute motion of objects being imaged ... also isn't a factor, as the maximum resoultion of JWST (the smallest pixels on an image) are still tremendous. It's possible that a nearbye (neighbouring galaxy) nova event might generate observable motion over days or weeks, but even that is unlikely. The interesting stuff in that event is actually the changes in brightness and evolution of light emissions, for the most part.

In the case of the Carina Nebula image 8,500 light years distant (that is, astronomically near), the individual dust segments are light years in length. The distance from the Earth to the Sun is roughly 1/64,000th that distance --- too small to visualise in thos images. The individual stars show are not dots or disks, but points, whose apparent size is a matter of refraction and saturation effects on the JWST itself.

Even where there migh be any movement, individual images are composed of multiple exposures and "stacked" to take median observed signal strengths. This is, in a way, to eliminate motion effects, but the moving entities are cosmic rays which create random signatures on the sensors of JWST, and not movement of the telescope or its targets themselves.

Re: Compare Webb's Images to Hubble

#92
post #89
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, exactly right. (AFAIK, IANAA)

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Re: Compare Webb's Images to Hubble

#93
The new scope appears to be capable of wonderful images, and no doubt many new discoveries.

Too bad, then, about the crappy colorizing/outlining for the 'so pretty' crowd. I await the site that simply shows (frequency-shifted) images. Any colorizing should have a 'legend' describing its purpose.

Re: Compare Webb's Images to Hubble

#94

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?

These are just the first few images. Give it time.

Re: Compare Webb's Images to Hubble

#95
post #40

I’m curious what’s going on in the upper left area of the Carina Nebula image. The dust can’t have actually cleared out that much since the Hubble shot was taken, could it?

With infrared you can see through the dust.

Indeed - that's one of the primary reasons to build the JWT: Dust and gas blocks our view in various cases so we want to take images in wavelengths that are more transparent to that debris.

Re: Compare Webb's Images to Hubble

#96

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…

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Re: Compare Webb's Images to Hubble

#97
post #74

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…

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 galaxy it could be a very dusty nearby galaxy (also appearing very red) but if I remember right, that would have a slightly different signature. Dusty galaxies often aren't entirely dusty and have "lanes/channels/streaks" of dust that are interspersed among normal stellar regions, so if it were that, you would be seeing some bright spots outside the infrared. But this one has the shape of a normal galaxy but red all over, suggesting something affects the whole galaxy -- i.e. redshift.

Re: Compare Webb's Images to Hubble

#98
post #42

Why is there so much more lens flare on Webb vs Hubble? It seems to negatively degrade the photos taken much more so than Hubble.

This is a great explanation: https://bigthink.com/starts-with-a-bang/james-webb-spikes/

This is interesting, thank you - going to pass this along to friends who were curious and got less informative answers :)

Re: Compare Webb's Images to Hubble

#99

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?

With respect, the goal of a major scientific project is not to impress the layperson with pretty pictures.

Re: Compare Webb's Images to Hubble

#100
post #66

To touch the stars. To reach a galaxy. To dream of afar. And in the deepest space, see our ancestry.

It's hard to look at the Webb images without thinking that there must be life and technology out somewhere else in the stars.

Reading the selfish gene is making me think the same thing.
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