Talk:Redshift/Archive 11

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Hubble on Expanding Universe

It should be noted in the section on the expansion of space that Hubble later questioned the validity of this theory. On the Problem of the Expanding Universe, Edwin Hubble, American Scientist 1942

If, then, we analyze our data, if we map the observable region, using first one scale and then the other, we may find that the wrong scale leads to contradictions or at least to grave difficulties. Such attempts have been made and one scale does lead to trouble. It is the scale which includes the dimming factors of recession, which assumes that the universe is expanding.

Hubble provides a grave review for expansion interpretation. He also stated that

It merely removes the theory from immediate contact with observations.

Given this factual information, this article should make note of Hubble's positive and negative remarks in order to keep it neutral to Hubble's position. Orrerysky (talk) 20:34, 30 November 2013 (UTC)

The authoritative source on this subject in Cosmology and Controversy by Kragh. In that work, it is clear that the context of Hubble's questioning was one based on his failure to measure the distances to the spiral nebulae properly. His remarks were that either his measurements were wrong or that the expanding universe was wrong. It turned out that his measurements were wrong (he was not looking at Cepheids and instead was looking at H II regions and so he thought the galaxies were much closer and thus the Hubble Constant was much larger). jps (talk) 23:23, 30 November 2013 (UTC)

Anomalous Objects

Shouldn't the curious case of the NGC 7603 be discussed and incorporated into the article? By the configuration of the system, there is a galaxy, a quasar and two faint objects which share the same space (not backgrounding), and they all have different Redshift momentum, how can this be explained? Eduemoni^↑talk↓ 16:08, 9 February 2013 (UTC)

This is not acknowledged by anyone other than Halton Arp to be "not backgrounding". jps (talk) 23:24, 30 November 2013 (UTC)

Redshift used for Radar Guns?

This article claims that Redshift is used in Police Radar Guns. However, these devices are not "spectroscopes" and do not measure redshift. This effect should be properly attributed to Pulse Reflection Orrerysky (talk) 20:08, 30 November 2013 (UTC)

Doppler radar and radar gun both disagree with you, and cover the topic in rather more detail.--JohnBlackburne^words_deeds 20:27, 30 November 2013 (UTC)

radar gun does not appear to be a spectroscope capable of analyzing absorption lines. Unrelated topic. Orrerysky (talk) 20:34, 30 November 2013 (UTC)

Please read it again: it does not say spectroscopes are used in radar guns.--JohnBlackburne^words_deeds 20:50, 30 November 2013 (UTC)

The Redshift Effect is very specifically in regards to the measure of absorption lines & emission lines in a spectrograph. Given that radar gun is not measuring a displacement in absorption or emission lines, I fail to see how it relates to the topic. I propose this section be removed and added to Pulse Reflection Orrerysky (talk) 20:54, 30 November 2013 (UTC)

"Redshift" refers to the shifting of the spectrum of an object toward longer wavelengths. It does not refer to simply measuring absorption and emissions lines in a spectrograph otherwise there would be no such thing as photometric redshift, for example. jps (talk) 23:20, 30 November 2013 (UTC)

That's great, perhaps you can explain to me how a radar gun works to measure redshift when its specifically calibrated for Pulse_(physics)#Pulse_Reflection of a signal with the same frequency and wavelength as what was emitted. This is bad science and misrepresents both redshift, pulse reflection, and radar guns. Orrerysky (talk) 16:19, 1 December 2013 (UTC)

Most radar guns use Continuous-wave radar. jps (talk) 23:11, 1 December 2013 (UTC)

Nonlinear scaling factor

The Hubble red shift problem must be generalized mathematically to include other scaling factors than linear. Try searching Google with the phrase "Hubble red shift exponential". SyntheticET (talk) 20:43, 20 September 2014 (UTC)

Edit 6 March

Can you explain why "none of these edits really helped"? Especially since it's my understanding that the current text is factually wrong. Banedon (talk) 01:13, 7 March 2014 (UTC)

suspected error in redshift for theta= 0 formula

under redshift formulae in the dopler effect section it says:

$1+z={\frac {1+v\cos(\theta )/c}{\sqrt {1-v^{2}/c^{2}}}}$

and for motion solely in the line of sight (θ = 0°), this equation reduces to:

$1+z={\frac {1}{\sqrt {1-v/c}}}$

I'm pretty sure this is simply not true. I cannot get to that form.

can anyone verify?

Indeed, I fixed it. Thanks for pointing out! Banedon (talk) 14:24, 11 November 2014 (UTC)

Redshift as an unsuitable measure of distance

An essential requirement for any measure of distance is additivity for collinear points. i.e. if A, B, C are on a straight line (or geodesic) then dist AB + dist BC = dist AC. It is easy to verify that redshift does not have this property. As a result redshift measurements are dependent on the point from which they are measured. Usually the point of measurement is the Earth leading to a geocentric view of the Universe not satisfying the cosmological principle. JFB80 (talk) 02:39, 25 March 2016 (UTC)

To address your precise point: You've defined "measure of distance" as a linear quantity. Redshift, however, is in general a nonlinear function of distance. For example, using the Friedmann-Robertson-Walker metric, redshift is the ratio of the scale factor a(t) at the time of observation to a(t) at the time of emission, where a(t) is nonlinear. So redshift is an indicator of distance, but not a "distance measure" per se.Karl pomeroy (talk) 21:04, 3 July 2016 (UTC)

Indeed. I don't get your point though, because it's possible to derive distance from redshift, it's just sensitive to other parameters. And while additivity does not hold, other relations do, so given the redshifts to B and C from A, one can work out the redshift to C from B. Banedon (talk) 02:47, 25 March 2016 (UTC)

Thank you for your reply. I have been trying to understand how cosmologists in practice estimate distances from redshifts. I don't find this clearly explained, perhaps you can. It seems to me you can get either (a) a (possibly rough) estimate of time the light takes to travel or (b) make some assumption about the model and so use theoretical formulae to find a(t) and then hopefully the distance. My remarks were prompted by the thought that, most often, redshift is used to characterize distance and with the commonly used definition (which seems to be incorrect), a distorted picture arises.JFB80 (talk) 06:34, 28 March 2016 (UTC)

Well part of the problem is that 'distance' has multiple meanings in cosmology, and furthermore is sensitive to other parameters such as the density of matter and / or dark energy. In other words, the "distance" (using this loosely, since there are different meanings of distance) to a faraway body is not the same in a universe with zero dark energy compared to one in which dark energy makes up ~70% of the universe and matter the remaining ~30%. There is a formula for it, which as far as I recall is an integral equation that has to be evaluated numerically. Light travel time is much easier, since the speed of light in a vacuum is a constant so simply dividing the "distance" by the speed of light grants the time. This might help: [1]. Banedon (talk) 06:48, 28 March 2016 (UTC)

To clarify further: redshift is the observable quantity. Distance is the derived quantity. Since we can't directly measure distances, we might as well carry around the thing we can measure. Astronomers refer to redshift as it is independent of a particular set of cosmological parameters, so that as those parameters are refined (via e.g. CMB, BAO, or Supernova measurements), we can trivially update our distances. As Banedon alluded to, you can derive many different useful "distances" from the redshift and the cosmological parameters, so the thing to hang on to is the base quantity. To compute your distance of choice from redshift, you have to (almost always numerically) integrate the Friedmann_equation. Ned Wright's Cosmological Calculator is a handy way to play with this.

This could probably be made more clear in the article. - Parejkoj (talk) 16:33, 28 March 2016 (UTC)

Yes I think the algorithm should be explained in simple terms. To find light-travel time and distance for nearer objects seems fairly simple using Hubble's original law. But in general Friedmann's equation must be integrated numerically to find H(t). Then how is distance found? Is it obvious as I don't see that explained anywhere in Wikipedia? Presumably it is programmed in Ned Wright's calculator but that needs a lot of deciphering. JFB80 (talk) 21:07, 29 March 2016 (UTC). I think the distance must be found by integrating incremental distances using the time-variable Hubble Law but as I said it is not made clear anywhere.JFB80 (talk) 21:46, 29 March 2016 (UTC)

No, it's not obvious how redshift is transformed into "distance" (again, using the word loosely). This is material typically covered in an advanced undergraduate course in cosmology. A quick search on Wikipedia does show some coverage though: Distance measures (cosmology). I'm woefully short on time though, and can't add it to this article. Banedon (talk) 09:33, 31 March 2016 (UTC)

Thank you for the comment. The most direct method seems to be the Mattig formula. JFB80 (talk) 17:07, 1 April 2016 (UTC)

That formula is not valid for the universe we live in: we have dark energy, while it assumes Omega_lambda=0. There really is no closed form solution for our Universe. The best discussion of this on Wikipedia is section 1 of Distance measures (cosmology), which was clearly written based on Hogg (1999), which it references. I've added a couple sentences to it to try to clarify things. If you think this helps, we should like to that article from section 3.2. It would be nice to reference Barbara Ryden's Cosmology book as well, in that section.. - Parejkoj (talk) 19:06, 2 April 2016 (UTC)

Cosmic Redshift Mathematical Derivation

The mathematical derivation of cosmic redshift (section 3.2.1) based on the Friedmann-Robertson-Walker metric looks absolutely rigorous. However, when I apply this step-by-step procedure (breaking up and recombinging the integrals) to the Schwarzschild metric, I get a blueshift rather than a redshift, ie. the wrong answer. I have tried several variations on the integrand and the limits of the integral, and have even tried varying the speed of light. All attempts produced a blueshift or no shift at all. Obviously, this could be my own systematic errors. Does anyone know whether this procedure is truly rigorous? Or is there some hidden assumption that makes it work for the FRW metric but not other metrics? It should work for every metric. Karl pomeroy (talk) 20:22, 3 July 2016 (UTC)

Sounds like a sign error. Make sure you're using the right signature. jps (talk) 19:20, 16 March 2017 (UTC)

Error/lack of clarity in geodesic equation

The geodesic equation is quoted as:

$ds^{2}=0=-c^{2}dt^{2}+{\frac {a^{2}dr^{2}}{1-kr^{2}}}$

and all symbols other than "r" are defined. Generally an equation in physics should work no matter what system of units is chosen but this not the case here and "r" and "dr" do not appear to be related in the way one would expect.

Elsewhere I found that "k" can only take values 1, 0, and -1 (dimensionless). $1-kr^{2}$ also has to be dimensionless so this should be written as $1-{\frac {kr^{2}}{Rmax^{2}}}$ where Rmax is some maximum value of r (which has to be the case if k = 1). Alternatively, if "r" is by convention a dimensionless fraction of Rmax (which should be explained) then one assumes "dr" is also dimensionless and something needs to be added to the expression $c^{2}dt^{2}$ to make that dimensionless.

88.10.216.37 (talk) 11:46, 23 November 2015 (UTC)Alan Williams-Key

r and dr are related in the usual way if you are careful about where in the manifold you begin to do the path integral. You cannot start at a singularity, for example (a place where the curvature is infinite). However, starting anywhere else will yield a coordinate value for each point. The "global curvature", then is related to the distance away from wherever you start and indeed, in this formulation, k carries along units. The reason this works is because of the cosmological principle, incidentally, which means that there is only one value for the curvature in your entire 3-D space (if you had more than this, you would violate either isotropy or homogeneity). jps (talk) 13:41, 1 April 2017 (UTC)

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Simplification & clarification in 'Redshift formulae' section

In top-right panel of table, TBond combined two expressions for $1+z$ into one equation. Before, section used both $v$ and $v_{\parallel }$ for velocity.. TBond got rid of $v$. TBond (talk) 04:40, 5 December 2017 (UTC)

Suggestion to help the simpletons (We wave hello)

Just come from reading an article describing a discovery in terms of high red shifts.

As noted in the study, VST-ATLAS J158.6938-14.4211 (J158-14 for short) has a redshift of 6.07, while VST-ATLAS J332.8017-32.1036 (J332-32 for short) was found at a redshift of 6.32.

But since the great interest there was the immense estimated mass of the central black holes - in relation to time since Big Bang - I had hoped to come here to 'translate' the red shifts to time since Big Bang. No joy.

There are mentions of some example red shifts and sometimes what those particular numbers translate to as 'age'. But no simple table to relate red shift number to 'age'. A volunteered diagram at Highest redshifts gives approximate red shift numbers to apparent distance, but that has an uncertain translation to 'age'.

Could someone put together a bare table of red shift numbers to 'ages'. I'm thinking 6.0 is around 12.7-12.8 billion years, but gee, numbers like that make me woozy! :) Shenme (talk) 20:36, 12 March 2018 (UTC)

Should say more about Arp's theory perhaps in historical section

Although this is no longer regarded as a valid theory it was back in the 1970s and 80s and I think of historical interest for that reason. When I was young, although his was a minority view it was scientifically respectable. The encyclopedia article expresses it accurately though of course we can't copy it - just to give an idea of the tone to aim for and it's historical interest. Also relevant today because people who are doing junk science sometimes cite his work as if it was currently valid as an objection to red shift. To explain his ideas briefly but also the observations that his theory was unable to explain would be very useful I think. [2] Robert Walker (talk) 04:41, 19 April 2018 (UTC)

Arp's work doesn't belong in this article: it is very much WP:FRINGE. - Parejkoj (talk) 17:26, 19 April 2018 (UTC)

Inertial Redshift article redirected to Expanding Universe section

Hi all, I have used the "blank-and-redirect" tactic to redirect the Inertial reference article (https://en.wikipedia.org/w/index.php?title=Inertial_redshift&redirect=no) to the expanding universe section of this article. It seems that it is only tangentially visited in relation to Hubble's law and serves to confuse readers. I find that it is in violation of multiple Wikipedia polices and that the original editors (Newmanok) have only made contributions to this article and that, since then, only very small improvements have taken place, mostly in grammar. The entire article relies on 2 online articles that are not peer reviewed and have been downloaded less than 200 times each. They are not trustworthy scientific sources at this point. Further, I can find no reference to inertial redshift as it is described in this article. Thus, I believe this article violates wp:no original research and WP:Verifiability as well as clearly fails to meet the criteria for wp:notability. As all subsequent editors, since 2015, have only fixed grammar (and added in the second source by the same author in the same online journal), I do not expect any of the editors to object (there have only been 7 total edits since 2015). Also, the only entry ever on the talk page was by an editor, User:Felisse, who asked a question that never got a response, in 2016. As per WP:Redirect, I started this talk page section on the target article with the intention of notifying the editors of the change and reasons for them, as well as allow for objections. You can check the most recent version of the article, before the redirect, at https://en.wikipedia.org/w/index.php?title=Inertial_redshift&oldid=961674989. Thanks! Footlessmouse (talk) 04:24, 17 August 2020 (UTC)

Merge blueshift into redshift

Apart from a few specific examples, the blueshift article seems completely redundant with the redshift page. Does blueshift really need its own page? I think potential readers would benefit more from a page ("Redshift and blueshift") that treats both concepts simultaneously.163.158.132.63 (talk) 22:37, 23 January 2021 (UTC)

Yes, these concepts are obviously complimentary and would be better dealt with a single article. Support merge. Furthermore, the blueshift article is far shorter and inferior in quality to the redshift article. Most of the decent information within it seems to just be copied and rewritten from the redshift article. Martinthewriter (talk) 14:22, 23 July 2021 (UTC)

Support merge for the reasons given above. Since the name would become "Redshift and blueshift", with redirects from Redshift and Blueshift, it becomes unimportant which has the best current article or the more familiar name. --MadeOfAtoms (talk) 21:05, 24 July 2021 (UTC)

Support merge for the reasons above — Preceding unsigned comment added by 2001:569:54FE:9F00:5C06:355B:9A49:30EB (talk) 21:17, 6 November 2021 (UTC)

Support merge. I can begin the merge process. Marisauna (talk) 01:27, 18 November 2021 (UTC)

Updating Highest redshift section

Someone with more editing skills than I should update the Highest redshift section of the article (current z=11), since a redshift of z=13.27 has been detected from HD1 (galaxy) (as of 07 April 2022) Thanks! zCryophoenix 21:47, 8 April 2022 (UTC)

English

I removed "Original Research" that, on the face of it, was, to me, obviously incorrect. I removed the phrase "perhaps indicating that up to that point its German equivalent, Rotverschiebung, was more commonly used." I doubt this very much, particularly in light of the preceding sentences in the same paragraph this phrase was in. The English language always adds the adjective in front of the noun. When the adjective-noun pair are in fact naming a particular thing a hyphen is used. E.g. red ball vs base-ball or basket-ball. Thousands of times the hyphen is dropped when the particular thing is perceived as distinct and in need of its own noun. In point of fact base-ball and basket-ball became baseball and basketball in the same decade as red-shift became redshift. This has absolutely happened in English since its inception 1,500 years ago. Nick Beeson (talk) 18:10, 16 July 2022 (UTC)

Earliest use in print

This article states that "The earliest occurrence of the term red-shift in print (in this hyphenated form) appears to be by American astronomer Walter S. Adams in 1908". However, the listed citation does not appear to support that, and the OED specifically disagrees, stating that "The concept was described by W. S. Adams in 1908 in connection with the effect of the rotation of the sun on its spectral lines (Astrophysical Jrnl. 27 213–18), but the term redshift was not used. A 'shift towards the red' is mentioned in Astrophysical Jrnl. (1897) 5 210." The earliest use that OED offers is by Arthur Stanley Eddington in 'The mathematical theory of relativity', 1923. I'm loathe to start editing a featured article on which I'm very far from an expert, hence why I'm not tackling this myself - I don't want to inadvertently introduce an error. OpenToppedBus - Talk to the driver 12:58, 4 October 2022 (UTC)

I couldn't find the statement in the references either. Adams was primarily interested in stellar spectra, so I'm not sure why he'd be referencing nebular red-shift. Praemonitus (talk) 02:29, 16 March 2023 (UTC)

Classical redshift

This article primarily focuses on relativistic redshift. I added a section on classical redshift for transparency and balance. This was promptly reverted by Parejkoj (talk). Is there any support either way? I can understand that supporters of relativity may not like or agree with the new section but it is well cited, well illustrated and factual. The oracle 2015 (talk) 20:32, 23 April 2023 (UTC)

A hodgepodge of youtube links (youtube is not a WP:RS for science articles) and repeated citations to Feynman aren't enough to make this relevant. This page is about cosmological redshifts, not classical Doppler shifts. - Parejkoj (talk) 21:01, 23 April 2023 (UTC)

With respect, this article is titled ‘Redshift’, not ‘Cosmological redshift’. I am absolutely certain that a section on the redshifting of light belongs in this article.

I understand about the citations so would it make a difference if the new section is better cited? The oracle 2015 (talk) 21:24, 23 April 2023 (UTC)

I will reinsert the new section on classical redshift. The assertion that this page is only for cosmological redshift is redundant because classical redshift is cosmological in almost all scenarios. I have inserted more reliable sources and I will continue to improve the new section.

Please note, this is a good faith edit and I draw everyone’s attention to Wikipedia’s policies on reverting: three-revert rule, edit warring and reverting.

If other editors find fault with the new section, it would be extremely helpful if they can improve upon it rather than just revert it. The oracle 2015 (talk) 08:36, 24 April 2023 (UTC)

The problem is, as above mentioned, the citations either don’t mean anything (I can assure you having read the Feynman book that he says nothing of the sort) or are unreliable, and I genuinely cannot tell what the section is trying to say anyways.

On revert policy, please see WP:BRD Fermiboson (talk) 12:01, 24 April 2023 (UTC)

Your difficulty in understanding is not a reason to revert. Almost everything on Wikipedia could be reverted on the basis that someone doesn’t understand something.

The Feynman book says what I cited in the chapter on mirrors. How light interacts with matter is basic QED. All other citations are articles on how light interacts with matter. The section essentially demonstrates how redshift occurs classically by the Doppler effect. The oracle 2015 (talk) 12:23, 24 April 2023 (UTC)

How is QED relevant to how light bounces off mirrors? And as above noted, the actual section relevant to what you are talking about is at Doppler effect#General. Fermiboson (talk) 12:39, 24 April 2023 (UTC)

QED is all about how light interacts with matter, including mirrors. Light can not bounce off of mirrors, it’s impossible. This is the article on redshift and my new section was concerning the redshift of light. The oracle 2015 (talk) 12:47, 24 April 2023 (UTC)

For the purpose of “classical” redshift, light very much does bounce off mirrors. Citing a technically correct but practically useless interpretation of the way mirrors work is not helpful, to WP:AGF, and the section mentions both an increase and decrease in wavelength, ie both redshift and blueshift, and by this simple evaluation already clearly belongs in the general article of Doppler shift, not one about the astronomical phenomenon of redshift. Fermiboson (talk) 12:53, 24 April 2023 (UTC)

Light simply can not bounce off of a mirror, learn about mirrors and QED, you will be fascinated. The oracle 2015 (talk) 13:07, 24 April 2023 (UTC)

I know about mirrors and QED. I have read the Feynman book. I am more fascinated by your claim to know QED but inability to elaborate on anything with regards to it. Knowing that Newton's laws are not strictly correct because of relativity does not stop us from using it to explain how a car moves. Similarly, knowing that geometric optics is not strictly correct in the quantum limit does not stop us from using it to explain classical effects. Fermiboson (talk) 13:16, 24 April 2023 (UTC)

The article on Relativistic Doppler effect delimits its scope as follows:

Astronomers know of three sources of redshift/blueshift: Doppler shifts; gravitational redshifts (due to light exiting a gravitational field); and cosmological expansion (where space itself stretches). This article concerns itself only with Doppler shifts.

For this article, perhaps we should have a similar statement:

Astronomers know of three sources of redshift/blueshift: Doppler shifts; gravitational redshifts (due to light exiting a gravitational field); and cosmological expansion (where space itself stretches). This article concerns itself with gravitational redshift and cosmological expansion. For Doppler shifts, see Relativistic Doppler effect and Doppler effect.

Prokaryotic Caspase Homolog (talk) 22:32, 26 April 2023 (UTC)

I’m not entirely sure if that is style compliant, but perhaps we could add an italic disambig along the lines of “This article is about the cosmological effects of gravitational redshift and redshift caused by cosmological expansion. For redshifts caused by Doppler shifts, see Relativistic Doppler effect and Doppler effect.” Fermiboson (talk) 08:41, 27 April 2023 (UTC)

An alternative might be to move this Redshift article as-is to Cosmological redshift (which currently redirects to Hubble's law), and retain Redshift as a short article explaining only "what is redshift?" i.e. its phenomenological meaning and its detection/measurement (rather than a disambiguation page) and then use {{main}} hat notes for Cosmological redshift and Relativistic Doppler effect in a section and brief paragraph about each; then add {{about}} hat notes ("for [the other meaning(s)], see [article(s)]") to the destination articles, as already suggested. — Jon (talk) 01:29, 28 April 2023 (UTC)

I think WP:COMMONNAME applies here. There's no need to complicate the lookup of the topic when it's the most likely reason to access it. An editor is always free to create a stand-alone article on "classical redshift", then see how well it stands on its own merits. Praemonitus (talk) 03:53, 28 April 2023 (UTC)

It’s a good question, though: why does cosmological redshift redirect to Hubble’s law, not here? Fermiboson (talk) 08:18, 28 April 2023 (UTC)

Presumably because this article covers other astronomical sources for redshift, whereas Hubble's law is pure cosmology. Praemonitus (talk) 14:27, 28 April 2023 (UTC)

Wikipedia:Unreviewed featured articles/2020/2004–2009

This article was reviewed as part of this drive - Wikipedia:Unreviewed featured articles/2020/2004–2009

I believe this article does not satisfy the Featured Article criteria and it will go to a Featured Article Review in due course if the article is not updated. A list of problems is noted below;

• There is a list in the lead
• The Measurement, characterization, and interpretation section has too few refs
• The Doppler effect section, too few refs
• The Mathematical derivation section is not encyclopaedic and not directly relevant
• The Extragalactic observations section has too few refs and unreferenced paragraphs
• The Effects from physical optics or radiative transfer section has too refs
• The Doppler blueshift section has an unreferenced list

Desertarun (talk) 09:37, 26 January 2023 (UTC)

I agree that the references need work. Here's some additional comments based on a quick perusal:

• The lead needs to improve
• Not all variables in the Redshift formulae table are defined in proximity to the table. Do they need to be presented there, since they are derived below?
• There are a lot of duplicate links in need of pruning, per MOS:DUPLINK
• Some bloated paragraphs hinder the flow
• Some format inconsistencies are apparent in the reference list

There's a lot of clutter from multiple sidebars, but I don't know what can be done about that. Please could somebody notify WP:AST when this article goes to FAR? Thanks. Praemonitus (talk) 18:30, 14 March 2023 (UTC)

I prosified and somewhat reorganized the lead. No comments as yet on the other points raised. XOR'easter (talk) 05:10, 13 June 2023 (UTC)

redshift diagram seems wrong

The redshift diagram at the upper right, though attractive, might be fundamentally wrong. It looks like the two sides are shifted by a constant amount. But when the absorption lines get redshifted, shouldn't the shift in the red line be about 30-35% more than the shift for the blue or cyan line? Example image: https://stokes.byu.edu/teaching_resources/redshift.jpg . Please don't say it looks fine: any confusion to a new learner can persist forever.

2601:247:4500:2330:3968:30FF:689E:E984 (talk) 20:26, 11 August 2023 (UTC)

The arrows look like they're all at the same angle, but the absorption lines themselves look right? It's rather hard to tell. The page it was originally taken from is no longer online, but here's a copy of the description that goes with the image from the archive, if that helps. - Parejkoj (talk) 14:16, 12 August 2023 (UTC)

I decided to adapt the image from the link I mentioned above to be this: [3]https://drive.google.com/file/d/1Wj9b1qV6Z4A3VnyoYg8qVQt4vsAXpsZU/view?usp=sharing . redshift at z~0.07. you can see (barely) that the red line is more shifted than the blue line.

2601:247:4500:2330:B5C2:1FD:20B5:6D3 (talk) 16:47, 26 August 2023 (UTC)