Talk:Webb's First Deep Field: Difference between revisions

Where in the sky

Just for reference, could we get the RA/Dec coordinates of this part of the sky?  Denelson83  02:29, 12 July 2022 (UTC)

User:Denelson83 sorry it's not letting me reply to you directly in this talk page for some odd reason

anyway, you may know better than i do if this is the right information at all, but according to the NASA/IPAC Extragalactic Database (if i'm reading this right), the coordinates are 284.993575, -23.708009 [1] Ayyydoc (talk) 02:48, 12 July 2022 (UTC)

"As it appeared 4.6b years ago"

Does this picture not depict the galaxy at different times, and different stages of evolution (if the scales involved are big enough?) due to the varying distances the light has traveled? Does anyone have accurate estimations of the ages? 102.219.79.151 (talk) 08:45, 12 July 2022 (UTC)

Came here to make this (or a similar) point about this phrase: It is inaccurate and unworthy of us, as the image actually shows how that section of the sky appeared six months ago (or whenever exactly it was recorded). The light left its sources 4+ billion years ago (and much longer ago in some cases ~ the point of the whole exercise), but in now way can we say that is how it was nor how it appeared then. Happy days ~ Lindsay^Hello 09:25, 12 July 2022 (UTC)

We're not really talking about how that section of the sky looked like, but how a "think" looked like, that is, it's actual appearance. However I agree there's a bit of ambiguity here as some objects might be younger/older depending on the distance, and not all objects are uniformally far away at the same distance. BeŻet (talk) 13:01, 12 July 2022 (UTC)

Given that the light travels (generally) unimpeded through space -- what do you think would make it change in the intervening 4.6 billion years? That is the entire point. Think of it as a snapshot that is traveling through space -- the snapshot will not change. The snapshot eventually reaches you. Although it is correct to say that the snapshot reached you (reached the telescope) 6 months ago or whenever it was received -- it is ALSO TRUE to say that the snapshot is an unaltered glimpse of what was there 4.6 billion years ago. If the light had been impeded, blocked, changed, absorbed and re-emitted, distorted, deflected, etc. the image (snapshot) would be very, very different. So -- think of the primordial light as a non-changing snapshot (a Polaroid! LOL) traveling through space ... taking 4.6 billion years to get to you. Chesspride216.144.161.51 (talk) 18:36, 12 July 2022 (UTC)

I've already updated the article for SMACS_J0723.3-7327 because of this. This galaxy cluster, which was the central target for this image is located at a redshift of z=0.390. First of all this gives us a lookback time of ~4.35 Gyr (not 4.6 Gyr as it's stated on NASA's website (https://www.nasa.gov/image-feature/goddard/2022/nasa-s-webb-delivers-deepest-infrared-image-of-universe-yet), but it could be easily an error made by the article writer). Also lots of articles over the internet cites this as "this cluster is located 4.6 billion light-years from Earth", which is even worse, since the z=0.390 redshift gives us a proper distance of ~5.12 Glyr. (All these values were obtained using the cosmology determined by the Planck 2018 results.) Masterdesky (talk) 13:38, 12 July 2022 (UTC)

These kinds of small adjustments are needed, of course, but the general point remains. Chesspride216.144.161.51 (talk) 18:38, 12 July 2022 (UTC)

And of course the cluster is no longer where it was 4.6 billion years ago -- which is why the language is loose. Agree 100 percent on the minor adjustments. Chesspride216.144.161.51 (talk) 18:40, 12 July 2022 (UTC)

References

a grain of sand held at arm's length

How much is that in football fields? Or, snark aside, can we get an actual angle? -- Seelefant (talk) 13:57, 12 July 2022 (UTC)

Table 6 in the paper by Repp and Ebeling referenced in the SMACS_J0723.3-7327 article gives an angular separation of about 2 arcminutes between the BCG and second-brightest galaxy, FWIW. 142.113.134.91 (talk) 03:38, 13 July 2022 (UTC)

"Grain of sand" / "speck of sky" is an important fact about the image that the average reader won't know. An actual angle would be great to include if there's an RS for it, but it will be meaningless to the average reader. Levivich^[block] 15:13, 12 July 2022 (UTC)

debatable. most people I know do know degrees. ;) -- Seelefant (talk) 20:42, 12 July 2022 (UTC)

References

First image taken or released?

Should this not say that it was the first operational image by the JWST to be released to the public? - Floydian ^τ _¢ 15:52, 12 July 2022 (UTC)

Was there a prior operational image that was not released to the public? Levivich^[block] 16:15, 12 July 2022 (UTC)

They could have been taken in any order and this was the one of the six chosen to be the teaser. - Floydian ^τ _¢ 16:57, 12 July 2022 (UTC)

Infobox

I feel that the image should be in an infobox of some sort; is there an infobox of space images or the like? Thanks, Urban Versis 32^KB ⚡ ^{(talk | contribs)} 23:10, 12 July 2022 (UTC)

i thought so too to be honest. there probably is an infobox, but one thing i DO know: none of the other deep field articles have infoboxes. i dunno if that's for lack of trying or if there's a consensus, but that seems to be how it goes. Ayyydoc (talk) 17:35, 13 July 2022 (UTC)

Yeah, I see your point. Urban Versis 32^KB ⚡ ^{(talk | contribs)} 17:38, 13 July 2022 (UTC)

I think it's just that no one has created one yet. Category:Astronomy image articles (and subcategories) doesn't have very many articles. Levivich^[block] 17:54, 13 July 2022 (UTC)

I'll have to ask around, but I have some experience in Templates and might be able to create an infobox for astronomy images. Urban Versis 32^KB ⚡ ^{(talk | contribs)} 18:06, 13 July 2022 (UTC)

FYI, Help:Designing infoboxes. You probably already know this but if you want to create a new one, the easiest thing to do is probably to fork (copy) an existing one (the closest one you can find), and then modify it as needed. Feel free to ping me if you want any help; I've never made an infobox but I have some familiarity with templates generally. Levivich^[block] 18:12, 13 July 2022 (UTC)

Thank you! Urban Versis 32^KB ⚡ ^{(talk | contribs)} 18:16, 13 July 2022 (UTC)

Actually, I found an infobox for it: Template:Infobox galaxy cluster. We could implement that into the page. Urban Versis 32^KB ⚡ ^{(talk | contribs)} 18:24, 13 July 2022 (UTC)

that'd be really awesome it'd really be beneficial Ayyydoc (talk) 18:20, 13 July 2022 (UTC)

Where is SMACS 0723?

It would be useful to identify which part and how much of the image is SMACS 0723. In the absence of other information, I assume that SMACS 0723 is the bright spot at the center of the photo and consists only of the 3 (or 5) barely visible galaxies within that bright spot. Is that correct or does SMACS 0723 consist of a different or larger area? Smallchief (talk) 08:53, 13 July 2022 (UTC)

great question !! to my understanding, the entire image depicts SMACS 0723 Ayyydoc (talk) 17:33, 13 July 2022 (UTC)

To paraphase an old cliche: A picture without a thousand words to describe it is just a picture. Smallchief (talk) 10:22, 14 July 2022 (UTC)

Distance and lookback time

I've already commented this info on the "As it appeared 4.6b years ago" section here, but the "4.6 billion years" value is not accurate, nor for the distance of the galaxy cluster, nor for the "as it appeared 4.6 Gyr ago" section. I'm aware that this figure is what NASA/JWST originally published discussing this image, but it can be shown with routine calculations that it's inaccurate.

There are quite a few distance and time measures exist out there, but here we should use the proper/co-moving distance (that are the same when observations are made from $z=0$)

$d_{C}(z)={\frac {c}{H_{0}}}\int _{0}^{z}{\frac {dz'}{E(z')}},$

when discussing the actual distance of the cluster from Earth and the light-travel distance/lookback time/lookback distance

$d_{T}(z)={\frac {1}{H_{0}}}\int _{0}^{z}{\frac {dz'}{(1+z')E(z')}},$

when describing how old the snapshot of this cluster is that JWST just captured. Due to the expansion of the universe these two are obviously different on these billion-year timescales.

Using the Planck 2018 results of $H0\approx 67.36$, $\Omega _{m}\approx 0.3153$, $\Omega _{k}=0.0$ and $\Omega _{\Lambda }\approx 0.6847$ and the cluster's known redshift of $z=0.390$, we can calculate the values above and get

$d_{C}(0.390)\approx 5.12\ \mathrm {Glyr} ,$

$d_{T}(0.390)\approx 4.35\ \mathrm {Gyr} .$

These results mean that the SMACS J0723.3-7327 is 5.12 billion light-years from Earth and the JWST image shows "how it appeared 4.35 billion years ago". Using different cosmological parameters, these results will differ. I'm not sure if this was the cause of NASA publishing this "4.6 billion years" figure, or whether it's a result of bad internal communication or something else. In my opinion these values above should be the correct ones. Masterdesky (talk) 09:21, 13 July 2022 (UTC)

If the sources say 4.6, we say 4.6 per WP:NOR. Levivich^[block] 16:10, 13 July 2022 (UTC)

I don't really agree, since first, WP:NOR explicitly states that routine calculations are not original research. Second, I already cited (above) a published article from ApJ that clearly says SMACS 0723 is measured at a redshift of 0.390, which unambiguously corresponds to the values I gave above (assuming Planck 2018). Even the official JWST website gives a closer value of "4.24 billion light-years" (and cites the z=0.390 value) on the information page of the image in the "fast facts" infobox (https://webbtelescope.org/contents/media/images/2022/035/01G7DDWW7FSRX0GAP43WFZ9JNH). The difference usually arise from using a slightly different set of cosmological parameters. I sticked with the Planck 2018 results, since those are the most widely accepted currently.

I still understand the unfortunate situation that the whole internet is now flooded with this "4.6" value, it plastered all over NASA's websites, the sources for that figure are clearly abundant. (Although they obviously just copied a single original source.) Masterdesky (talk) 18:40, 13 July 2022 (UTC)

Have you considered the possibility that NASA knows something you don't? These are not "routine calculations," and even if they were, we can't use our own calculations to contradict an WP:RS. If NASA's made a mistake, take it up with NASA, get them to issue a correction, or find another RS that provides a different figure, and then we can update our articles. Levivich^[block] 19:04, 13 July 2022 (UTC)

That's why I linked the description of the image itself on JWST's official website that contains the following: "Distance | Redshift of cluster is z=0.39 (about 4.24 billion light-years)".

My main problem with this situation is the lack of care regarding these values. Different distance measures in cosmology are differ for a very good reason. If we make a statement that "the distance of a far-away astronomical object is X", we always need to specify "what kind of distance" we're talking about. On Wikipedia see eg. elements of the list of the most distant astronomical objects. Almost every article there contains both the proper and the light-travel distance of the object or at least specifies explicitly, which one it uses.

If we're saying "how an astronomical object looked X years ago", then we're talking about it's "light-travel distance" or "lookback time" by definition. At least specify this in this article, when talking about the spatial and temporal distance of SMACS 0723 (which are equivalent only in case of the light-travel distance if we naturally set $c=1$). Masterdesky (talk) 10:57, 14 July 2022 (UTC)

References