[HN Gopher] Compare Webb's Images to Hubble
___________________________________________________________________
Compare Webb's Images to Hubble
Author : hexomancer
Score : 558 points
Date : 2022-07-12 18:41 UTC (4 hours ago)
(HTM) web link (johnedchristensen.github.io)
(TXT) w3m dump (johnedchristensen.github.io)
| ijidak wrote:
| This is perfect! Without this context it's hard to appreciate how
| much better Webb is!
| boomskats wrote:
| The sliders break when page zoom is anything other than 100% :/
| mholt wrote:
| 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 recently learned about
| redshift. Hubble's deep field images were very dark red/orange
| because further objects appear redder (into infrared) before they
| disappear to the observer. Webb's sensors are more red/infrared-
| sensitive than Hubble's, so along with extremely fine, super-
| cooled optics using exotic materials to align and capture every
| single photon, its red sensitivity allows Webb to peer deeper,
| further, and dimmer than we've ever been able to before.
|
| And I've read that the "spikes" coming off the brighter stars are
| generally from stars in our own galaxy and they're not lens
| flares. They're caused by the edges of the telescope. Hubble's
| stars would have 4 spikes in a cross; Webb has 6 in a snowflake
| because of the shape of Webb's mirrors having 6 sides. Or
| something like that.
| dr_orpheus wrote:
| The spikes are caused by diffraction of light around the struts
| supporting the secondary mirror. Hubble has 4 supports for the
| secondary mirror. JWST has 3 support for the secondary mirror,
| which because...physics (I don't know I'm not an optics
| guy)...manifests as 6 diffraction lines.
|
| https://en.wikipedia.org/wiki/Diffraction_spike
|
| EDIT: It may be caused by both the diffraction spikes from the
| supports struts and the shape of the mirror and aperture. I'm
| not really sure. The JWST images also seem to have two
| additional small spikes that look more like the diffraction
| pattern from a single strut, which could also be a support
| strut for a stop further down the optics chain.
| WorldMaker wrote:
| Apparently the Diffraction spikes come from both the primary
| mirror shapes and the struts holding the secondary mirror.
| The primary mirrors of the JWST are hexagonal which would
| explain hexagonal looking effects. The three struts are
| apparently designed so that two of the struts match the
| hexagonal mirror angles at all times and are "hidden" inside.
| (The third strut apparently sometimes causes two much smaller
| "horizon" spikes for very, very bright objects.)
|
| Hank Green on TikTok did a neat, quick demonstration in video
| form.
| dr_orpheus wrote:
| Oh, thank you that makes sense. And due to the folding of
| the mirror and launch envelope constraints they can't
| equally space the three struts such that ALL are inside the
| diffraction of the hexagonal mirror.
| mintyLemon wrote:
| Link to that Hank Green video on YouTube:
| https://m.youtube.com/watch?v=Y7ieVkK-Cz0
| kadoban wrote:
| They're not lens flares, but they're still an artifact of the
| system, which is probably what most people mean by "lens flare"
| anyway, due to lack of a better common term.
| JacobThreeThree wrote:
| According to the Wikipedia definition, I'd say that Webb's
| artifacts could be classified as "lens flares".
|
| >This happens through light scattered by the imaging
| mechanism itself, for example through internal reflection and
| forward scatter from material imperfections in the lens.
| Lenses with large numbers of elements such as zooms tend to
| have more lens flare, as they contain a relatively large
| number of interfaces at which internal scattering may occur.
|
| https://en.wikipedia.org/wiki/Lens_flare
| foxhop wrote:
| thank you very informative.
| [deleted]
| thatswrong0 wrote:
| Just needs to include exposure time differences and this is
| perfect. Glad to witness the power of this fully armed and
| operational battle station.
| laserbeam wrote:
| It's my understanding that Webb used much shorter exposure
| times than Hubble, correct?
| tambourine_man wrote:
| Yes, hours vs days, which makes them a lot more impressive if
| you know a bit about photography.
|
| I wanna see what this thing is able to do with a 10 days
| exposure. Let it loose.
| dylan604 wrote:
| >I wanna see what this thing is able to do with a 10 days
| exposure.
|
| Ever seen a solid white square? =)
|
| As with all things, it totally depends on what's being
| imaged. Exposing the Orion Nebula for 10 days would result
| in a totally over exposed image looking like a solid white
| square.
| nooyurrsdey wrote:
| This is a wonderful way to visualize side by side images like
| this.
|
| Great work, it feels smooth and intuitive.
| hparadiz wrote:
| I'm actually most looking forward to seeing a picture of our
| planets. I wonder what kind of resolution we'll get of Jupiter
| and Mars in particular.
|
| Also curious about what the closest stars to our solar system
| would look like. Of course it also makes me wonder what would we
| be able to see given a 100x increase in aperture. Like for
| example if we could send up something extremely large on
| Starship. Would we be able to image planets in our local group?
| Exciting!
| mtlmtlmtlmtl wrote:
| I love this. But the Carina Nebula doesn't work on Firefox for
| Android. It just displays the JWST image.
| yellowapple wrote:
| For me it shows the top half of the Hubble version, but not the
| bottom.
| wlesieutre wrote:
| That's the extent of the Hubble original
|
| https://hubblesite.org/contents/media/images/2008/34/2405-Im.
| ..
| mtlmtlmtlmtl wrote:
| That makes sense then. I have two suggestions if the person
| who made this is reading: maybe fill out the hubble image
| with black so it can line up with the JWST image, might
| make the interface less janky? Or if someone knows of a
| larger imagine from another telescope(Spitzer?) That could
| be a more interesting comparison for that particular
| observation.
| red_trumpet wrote:
| Changing the orientation of my phone from portrait to landscape
| while on the site somewhat solved this.
| protoster wrote:
| Bug report: On Firefox the difference wiper thing doesn't appear
| for the last image (Carina Nebula), it only shows the full Webb
| image.
| weaksauce wrote:
| funny enough that one didn't work on chrome but worked in
| firefox nightly albeit a distorted version that only showed the
| top left corner of it... I'm not sure hubble shot the full
| version?
|
| https://i.imgur.com/oBK3sWE.png
| nathancahill wrote:
| Working on latest FF on Mac. The Hubble image is just smaller.
| bandyaboot wrote:
| 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?
| dylan604 wrote:
| Lots of visible light is reflected in the Hubble image from the
| dust causing it to look like it does. As others have said, the
| JWST does not suffer from that as it "sees" past those
| frequencies revealing new details instead.
| CitizenKane wrote:
| I believe the Hubble shot is more in the visible spectrum
| whereas the JWST images are in infrared so there are structures
| in each shot that don't necessarily show up in the analogous
| image.
| treesknees wrote:
| I'm not an expert, but from what I came across online earlier,
| the Hubble telescope sees more of the visible/UV spectrum than
| the Webb telescope. So it may just be a difference in what's
| captured.
|
| This site has a diagram of the spectrum that shows which
| portions are covered by each telescope, as well as some video
| clips comparing photos captured by Hubble and Webb. The first
| video of the Lagoon Nebula (M8) demonstrates what I'm saying
| pretty well.
|
| https://webbtelescope.org/webb-science/the-observatory/infra...
| pkaye wrote:
| With infrared you can see through the dust.
| xenadu02 wrote:
| 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.
| wanderingstan wrote:
| Amazing! Would be interesting to also compare with earth-bound
| telescopes, to really appreciate the progress.
| prohobo wrote:
| Is it absurd to think that maybe the Carina Nebula's shape has
| visibly shifted a bit since the last photo?
| baltimore wrote:
| Now build a zoomable full-res version. Because I am spoiled and
| want the internet to do things for me.
| yread wrote:
| ESA got your back:
|
| quintet: https://esawebb.org/images/weic2208a/zoomable/
|
| https://esawebb.org/images/weic2208b/zoomable/
|
| carina: https://esawebb.org/images/weic2205a/zoomable/
|
| https://esawebb.org/images/weic2205b/zoomable/
|
| Southern ring https://esawebb.org/images/weic2207a/zoomable/
|
| https://esawebb.org/images/weic2207b/zoomable/
|
| https://esawebb.org/images/weic2207c/zoomable/
|
| Deep field https://esawebb.org/images/weic2209a/zoomable/
|
| https://esawebb.org/images/weic2209b/zoomable/
| mrleinad wrote:
| Well, I found my next set of ultrawide wallpapers for my 49"
| monitor :) Thanks!
| mtlmtlmtlmtl wrote:
| Not a UI or web guy scaling the slider with zoom might do the
| trick?
| angryGhost wrote:
| born too early...
| echelon wrote:
| For the machines that will replace us.
| bastardoperator wrote:
| 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?
| Mangalor wrote:
| These are just the first few images. Give it time.
| stevage wrote:
| With respect, the goal of a major scientific project is not to
| impress the layperson with pretty pictures.
| fleddr wrote:
| Pretty expensive Insta filter.
| _benj wrote:
| just WOW! I always feel so tiny when considering the absurd
| dimensions of space brought shockingly vivid with this images!
| supernova87a wrote:
| 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 different pixel size or imaging array size / focal
| length. Ok, the much larger mirror _is_ an achievement. But
| anyway, the resolution of the images is often not what really is
| the limiting factor for photometric observations. Yes it is
| sharper /higher resolution, but that wasn't the key selling
| point.
|
| The new thing is observations in the IR, which is somewhat a
| technical footnote in many gushing announcements of these images
| (or some discussion here too). And the general public knows
| little about that detail's importance, especially since the
| images are stylized / colored anyway to look just like RGB images
| that we are so familiar with. But everyone can easily appreciate
| a sharper image.
|
| Anyway, still a momentous achievement. And thank god we have a
| scientific field where stunning images was enough to get the
| public to support a $10B project.
|
| **
|
| Edit to add: I did not mean to detract from or diminish anyone's
| appreciation of the images and accomplishment at whatever level
| they are enjoyed. And of course many here are technically
| knowledgeable about the IR aspect. I just write to point out that
| for the most headline-grabbing images and newspaper writers, the
| sharpness of the images over the actual IR frontier is what grabs
| the attention.
| tigershark wrote:
| The increased resolution is extremely important given that the
| diffraction threshold is function of the wavelength and the
| mirror diameter. And you can clearly see that in the MIRI
| images at a longer wavelength that have a noticeably lower
| resolution compared to Nircam. If Webb mirror was as big as
| Hubble the resolution would have been bad in the long
| wavelengths. Hubble couldn't have had a better resolution with
| better instruments, he was already limited by its aberration
| problem and the new instruments were designed to mitigate that
| problem.
| nacogo wrote:
| 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/
| lisper wrote:
| Yes, exactly right. (AFAIK, IANAA)
| t3estabc wrote:
| how about now/ I am trying to get this to work and I am
| getting an error. That's fine I guess. I am just trying to
| get it to work. I am going to have to leave
| supernova87a wrote:
| 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.
| libraryatnight wrote:
| This is so dismissive and insulting. Slack channels at work are
| all abuzz about this today. Many of the boards and communities
| I visit are too, and while yes there's definite wowing on the
| resolution - all of them are talking about the IR. Trying to
| understand what it means and learn. Support reps through
| engineers at work asking questions, sending links. Even in the
| comments of reddit of all places people are curious. This is
| genuinely cool and people are engaging with it and you're
| dismissive of the public, the scientists, and just about
| everything in between.
|
| I'm sure you were well intentioned, but this comment read all
| kinds of rude and negative.
| Enginerrrd wrote:
| I think this is a little harsh, but I actually generally
| agree. I'm a total laymen here and my PRIMARY TAKEAWAY has
| been the IR component and how much more and further away you
| can see because of it.
| mtlmtlmtlmtl wrote:
| Right. After the initial "wow factor" has settled down, what's
| been most striking to me is the level of detail that's no
| longer obscured by gas and dust in these nebulae due to MIRI. I
| know very little about the study of stellar nurseries or
| planetary nebulae but I've seen enough pre-JWST images of them
| to know that astrophysicists just got a whole lot to sink their
| teeth into and I look forward to seeing further developments as
| more data is collected and existing data is studied.
| [deleted]
| matesz wrote:
| Did anybody make a comparison for rough estimation on the number
| of galaxies in the observable universe based on hubble vs webb?
| woevdbz wrote:
| It's striking how much more flamelike the structures appear to
| be, with the added resolution
| rnmp wrote:
| It's as if they remastered an old video game. So much more
| detail!
| avelis wrote:
| To touch the stars. To reach a galaxy. To dream of afar. And in
| the deepest space, see our ancestry.
| throwaway4837 wrote:
| It's hard to look at the Webb images without thinking that
| there must be life and technology out somewhere else in the
| stars.
| quickthrower2 wrote:
| Reading the selfish gene is making me think the same thing.
| dylan604 wrote:
| Why does that only come from Webb images? You weren't getting
| that same sensation looking at the Hubble images before? If
| that's true, then welcome to the club! It took you a bit
| longer, but we're happy you're here now. ;P
| 8bitsrule wrote:
| 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.
| jauntbox wrote:
| Very cool to see several galaxies that were entirely invisible to
| Hubble due to high redshift show up brightly to JWST.
| systemvoltage wrote:
| > This makes the Hubble telescope even more impressive in my
| eyes. Built 50 years ago with presumably 60 year old tech.
|
| > > Hubble telescope was funded and built in the 1970s by the
| United States space agency NASA with contributions from the
| European Space Agency. Its intended launch was 1983, but the
| project was beset by technical delays, budget problems, and the
| 1986 Challenger disaster. Hubble was finally launched in 1990.
|
| I commented on this other thread:
| https://news.ycombinator.com/item?id=32074242
| jcims wrote:
| Advantages of IR incredibly apparent in the last pic.
|
| Very nicely done!
| acqbu wrote:
| Hubble = iPhone 4S; Webb = Galaxy S22 Ultra
| UberFly wrote:
| Considering these are just the initial "test" images there is
| going to be some amazing stuff to come over the years. Can't
| wait.
| somenewaccount1 wrote:
| Thank you so much!!! I really wanted to see the difference side
| by side and this was an even better presentation. Really cool!
| hexomancer wrote:
| Just to be clear I did not create this website, I just saw it
| on reddit. All credits to the original author:
| https://www.reddit.com/r/woahdude/comments/vxeeqo/i_made_a_t...
| dynm wrote:
| 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 valid way of trying to understand things?)
| spenczar5 wrote:
| I worked in astronomy software for a few years for a different
| telescope, the LSST. I am not an expert, but I was in this
| world enough to answer.
|
| The short version - it converges faster (probably like 5-10x
| faster), but also (as everyone else said) works in different
| wavelengths.
|
| You can think of a telescope as a "photon bucket." The number
| of photons it collects is proportional to the area of the
| aperture. Webb's aperture area is 25.4 square meters, while
| Hubble's is 4 square meters, so roughly speaking JWST will get
| photons about 6 times quicker than Hubble.
|
| But that's only the roughest measure. Once you've got the
| photons, what do you do with them? You send them to a detector.
| There's loss in this process - you bounce off of mirrors, with
| some small loss. You pass through band filters to isolate
| particular colors, which have more loss. The detector itself
| has an efficiency; in CCD cameras people speak of "quantum
| efficiency" - the probability that a photon induces a charge
| that can be counted when you read out the chip. That quantum
| efficiency depends on the photon's wavelength.
|
| Furthermore - the longer your exposure, the more cosmic rays
| you get which corrupt pixels. You can flush the CCD more often
| and detect the cosmic rays and eliminate them, but you'll
| eventually brush against the CCD's read-out noise, which is a
| "tax" of noise you get every time you read out data.
|
| So this all get's complicated! People spend many years
| characterizing detection capabilities of these instruments, and
| write many pages on them.
|
| JWST's capabilities are described here: https://jwst-
| docs.stsci.edu/jwst-near-infrared-camera/nircam...
|
| HST's camera is more complicated to characterize, partly
| because it's older. Radiation has damaged and degraded many of
| the components so they have a lot of noise. The details of how
| this works are at the edge of human knowledge, so we don't have
| a great model for them. From the STIS handbook:
| Radiation damage at the altitude of the HST orbit causes the
| charge transfer efficiency (CTE) of the STIS CCD to degrade
| with time. The effect of imperfect CTE is the loss of signal
| when charge is transferred through the CCD chip during the
| readout process. As the nominal read-out amplifier (Amp D) is
| situated at the top right corner of the STIS CCD, the CTE
| problem has two possible observational consequences: (1) making
| objects at lower row numbers (more pixel-to-pixel charge
| transfers) appear fainter than they would if they were at high
| row numbers (since this loss is suffered along the parallel
| clocking direction, it is referred to as parallel CTE loss);
| and (2) making objects on the left side of the chip appear
| fainter than on the right side (referred to as serial CTE
| loss). In the case of the STIS CCD, the serial CTE loss has
| been found to be negligible for practical purposes. Hence we
| will only address parallel CTE loss for the STIS CCD in this
| Handbook. The current lack of a comprehensive
| theoretical understanding of CTE effects introduces an
| uncertainty for STIS photometry.
|
| Now - this was all about how _many_ photons you collect. When
| humans look at an image, they also care a lot about how fine
| the details are on it. This has to do with the resolution of
| the telescope 's imaging systems. Resolution is limited by the
| number of pixels on the detector, and (to a much lesser extent)
| by the optical train of the telescope - the aberrations and
| distortions introduced by mirrors that focus light onto the
| detector's pixels.
|
| Hubble has a high-res camera, and a separate wide-angle camera.
| Hubble's high-res camera actually outperforms JWST - it can
| resolve down to 0.04 arcsec, while JWST's can go to around 0.1
| arcsec. But JWST's camera has a much wider field of view.
| mtlmtlmtlmtl wrote:
| IANA{astrophysicist, space engineer} but I do follow this
| closely and have what I call a working armchair understanding
| of this stuff. Anyone from relevant fields is welcome to gently
| correct any imprecisions. I always want to learn more and will
| thank you for it
|
| >could Hubble achieve the same quality of images as Webb if it
| was given 100x (or whatever) more time exposure?
|
| No, for a different and simpler reason: Hubble isn't as
| sensitive in the infrared as Webb. A lot of the stars and
| structure Webb has revealed in the two nebulae especially is
| due to it picking up a lot more of the infrared light to which
| the gas and dust of the nebulae are essentially transparent. In
| other words the data is qualitatively different in addition to
| the increased resolution. This also will see much older light
| which is redshifted(the longer the travel, the greater the
| shift) out of Hubble's range of sensitivity.
|
| As for the quantitative part, I guess mirror size is what you'd
| want to look at? Hubble has a single circular primary mirror
| with a diameter of 2.4 metres.[0]
|
| Webb has 18 hexagonal mirror segments that are combined into
| the equivalent of a circular mirror with diameter 6.5m. That is
| ~6.25 times the light collection area of Hubble(25.4m2 vs
| 4m2)[1]
|
| 0: https://en.wikipedia.org/wiki/Hubble_Space_Telescope
|
| 1:
| https://en.wikipedia.org/wiki/James_Webb_Space_Telescope#Fea...
| lttlrck wrote:
| Plus, upgrading Hubble wouldn't get us close either. JWST is
| specifically designed to shield the sensors from IR/heat, and
| it's 1 million miles from Earth for a similar reason.
| nomel wrote:
| > That is ~6.25 times the light collection area of
| Hubble(25.4m2 vs 4m2)
|
| This would have to be scaled by the wavelength being
| observed, for a resolution comparison. Hubble actually has
| better absolute resolution, when viewing shorter the
| wavelengths that JWT can't sense (0.05 arcseconds vs JWT 0.1
| arcseconds).
| mtlmtlmtlmtl wrote:
| Right, that didn't occur to me at first, but is just
| obviously true when you point it out, thanks. Though I
| didn't know that hubble is actually higher resolution in
| that comparison.
|
| Then, in some sense, the first part of my explanation is
| most of the story in the case of comparing MIRI(mid-
| infrared instrument) to hubble in the near-infrared.
|
| But in comparing NIRCAM to Hubble in the near-infraread
| JWST would in fact have greater resolution, no?
| dylan604 wrote:
| No, expsoure time is not enough. Resolution is a factor of the
| size of the primary mirror. Exposure time just allows capture
| of photons at that resolution. With the JWST primary mirror
| dwarfing the Hubble's, then it will always have better imagery.
| 0xfaded wrote:
| Wavelength is also a factor. Huygens optics has a great video
| on this. tldr; angular resolution is about the same as the
| Hubble.
|
| https://youtu.be/gOpbXBppUEU
| red_trumpet wrote:
| 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.
| dredmorbius wrote:
| 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.
| IshKebab wrote:
| Motion of what?
| dontlistentome wrote:
| everything everywhere all at once
| spookthesunset wrote:
| Minor changes to the satellite position? Vibration from
| some hardware? I dunno but the parent asks a question I ask
| too.
|
| When you do long exposure, any kind of movement, even very
| small, can degrade your image.
|
| How JWST handles movement during long exposure is a good
| question. Same with hubble.
| adgjlsfhk1 wrote:
| long exposure images aren't actually 1 continuous
| exposure. you take a ton of individual images and
| composite them using known reference points.
| ryneandal wrote:
| Well I mean the JWST is in orbit both around the L2 point
| and the sun. It's sensitive equipment must also be facing
| away from the sun. So there's a lot of movement going on
| out there.
| dylan604 wrote:
| I'm sorry but no no no. These telescopes are tracking the
| objects they are imaging specifically to avoid imaging issues
| from motion. This isn't some dude in the backyard with an
| alt-az scope bought from a Sears catalog.
|
| I really hope you were trolling with this response
| ryneandal wrote:
| Here's out exposure time works for JWST: https://jwst-
| docs.stsci.edu/understanding-exposure-times
| pythonguython wrote:
| Not an expert, but one metric to demonstrate Webb's capability
| is that Hubble's deep field exposure took 10 days, and Webb did
| it in 12.5 hours.
| mtlmtlmtlmtl wrote:
| This is true, but he was asking specifically about a metric
| that's independent of the exposure time.
| unethical_ban wrote:
| Webb's physical dimensions are larger than Hubble's. The
| "collecting area" of Web is 273 sq ft to Hubble's 46, per
| Wikipedia. The two telescopes are sensitive to different (but
| somewhat overlapping) bands of light. Hubble worked through the
| visible spectrum while JWST is almost exclusively infrared.
|
| To the "can Hubble do anything Webb can do but with more time",
| the answer is no, due to the lack of mid-infrared sensitivity,
| among other things like atmosphere.
| rdsubhas wrote:
| A crude analogy is like this: Two cameras are pointed towards a
| wall. Camera #1 is good, but it is blocked by the wall. Camera
| #2 has a special trick, it does some magic that can look behind
| the wall.
|
| Now both have resolutions and stuff. But no matter how big the
| resolution or how long it stares, cam1 is fundamentally blocked
| by the wall. It can take extremely high res photos of things
| inside the wall, but it can never see anything behind the wall.
|
| Cam2 could have infinitely higher quality than cam1 -- because
| who knows, there can be 100, 1000, million or a never ending
| world of things behind that wall that can never be seen or
| captured by cam1.
|
| Cam1 is Hubble, cam2 is jwst, and the wall is infrared
| wavelength which is all around us. JWST can peer deeper and
| find hidden things into the _same point_ in space, which Hubble
| cannot because of it 's infrared wall.
| Osmium wrote:
| Regardless of exposure, you have to consider wavelength. There
| are some things JWST can see that are completely invisible to
| Hubble, or, similarly, there are objects that are opaque to
| Hubble that JWST can see right through. Just look at all the
| extra stars that appear in the image of the Carina Nebula for
| an example of that.
| agrajag wrote:
| For the wavelengths that the telescopes are designed to observe
| (primarily ultraviolet & visible for Hubble, though it can do a
| little bit of infrared, while JWST looks at Infra-red and mid-
| infrared) resolution is fairly comparable, though JWST has a
| much wider field of view and doesn't half to sit idle when it
| orbits the sun side of the earth like Hubble does.
|
| A major issue with Hubble & JWST comparisons is just that
| they're designed to look at different wavelengths of light. A
| lot of what JWST will see is completely invisible to Hubble,
| and no amount of observing time can compensate for that.
| masterspy7 wrote:
| Not trying to underscore this incredible achievement, but I'm
| curious if we could use AI techniques to upscale the Hubble
| images to achieve similar results as the Webb telescope. Has this
| been tried before?
| wetpaws wrote:
| No
| lynguist wrote:
| It's a valid thought, but it would really be like trying to
| take pictures of the sky from underwater and using AI to make
| it look like it was taken from out of water.
|
| This means: the AI has to predict what it is supposed to look
| like and for that we would need out of water pictures as
| reference in the first place which we didn't so far!
|
| And then: even if we have these new out of water pictures as
| reference, the AI generated ones would still not show what is
| real, but instead a fiction. The fiction can look believable
| but it cannot be studied to derive facts from it. It's like
| trying to study an AI generated language.
|
| This sounds like my friend who literally believes that buses
| will go extinct within 3-5 years as every vehicle will self
| drive. It's not thought all the way through.
| detaro wrote:
| AI upscaling works if you want a prettier picture, but not if
| you want to actually _know_ more. AI can 't magically conjure
| information that isn't there, so if you upscale it has to
| invent details to fill in. Which is fine for some use cases,
| but not for science or truth-finding.
| Kelm wrote:
| Sure you could try, but without getting real higher fidelity
| photos you'd never know how realistic the synthetic images are.
| [deleted]
| alberth wrote:
| 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.
| Dave_Rosenthal wrote:
| The segmented design of the mirror creates diffraction effects
| vs. Hubble's single mirror.
| kristofferR wrote:
| This is a great explanation: https://bigthink.com/starts-with-
| a-bang/james-webb-spikes/
| libraryatnight wrote:
| This is interesting, thank you - going to pass this along to
| friends who were curious and got less informative answers :)
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