Talk:Apparent magnitude

Table of notable celestial objects - too extensive

It seems out of place to have such an extensive listing of objects. Perhaps this table should only include truly 'notable' objects, and have its own page (or just link to a website with a similar table) for the extended version? All Clues Key (talk) 02:20, 15 September 2012 (UTC)

Table modified in accordance with this suggestion. All Clues Key (talk) 17:30, 9 October 2012 (UTC)

I have reverted you severe castration of the list as unnecessary. If you do not like the long list you can simply ignore that section. I think it is useful to list sample objects at many apmags. -- Kheider (talk) 18:17, 9 October 2012 (UTC)

As I said above (and received no protests or disagreements to), the current list in unnecessarily extensive and detracted from the overall readability of the article. Hopefully other editors will voice their opinions, but it doesn't seem like this is the right place to include an exhaustive list of apparent magnitudes. The purpose of the article is simply to explain what 'apparent magnitude' means and is. That being the case, providing **some** common, important examples of apparent magnitude is very helpful. A list that contains entries such as, "Sun as seen from Eris at aphelion", "Callirrhoe (small ~8 km satellite of Jupiter)", and "Jupiter if it were located 5000AUえーゆー from the Sun" seems completely subjective, excessive, irrelevant and unaesthetic. All Clues Key (talk) 18:51, 10 October 2012 (UTC)

You agreed with yourself, and I have protested the excessive removals. Your castrated version of the list included no object dimmer than Messier 33 @ apmag 5.7. How do you know people do not want examples of objects that require a telescope to actually see? Most objects simply are not visible without a telescope and obviously will not be as notable as naked eye objects. Many amateurs consider objects such as Uranus, Ceres, M81, Neptune, Titan, Pluto, Eris, the moons of Pluto, and Halley's comet as notable. -- Kheider (talk) 20:28, 10 October 2012 (UTC)

I agree with Kheider. The lengthy list is most interesting. Rothorpe (talk) 21:14, 10 October 2012 (UTC)

It will likely be very subjective, but I wonder if there is anywhere that could reasonably hold a list of planetary moons by difficulty of seeing them. It's not just magnitude but also proximity to the planet: Mimas is brighter than Oberon, but harder to see. Double sharp (talk) 09:16, 2 October 2021 (UTC)

Photometric Reductions

How is this related, if at all, to photometric reductions? ~jp

Needs improvement

This article is quite poorly organised and in some places poorly explained. For a relatively important atronomy article it is a bit disappointing. 86.160.222.250 (talk) 21:04, 18 March 2013 (UTC)

The explicit relationship between apparent magnitude, m, and power flux in watts per square meter, F, when m and F pertain to the same bandpass, is

m = −2.5 log F − 18.98224

Example. The sun's bolometric apparent magnitude, as seen from Earth, is −26.8167

m = −26.8167

F = 10^[−0.4(m + 18.98224)]

F = 1360.8 watts per square meter

50.110.104.0 (talk) 12:35, 6 March 2024 (UTC)

Move large table down so that readers needn't scroll down many pages to find formulae

While the extensive table has its uses (discussed above), readers have to scroll down many pages to find formulae to calculate magnitude. As the table mainly provides examples, I think it's reasonable to move it to the bottom to detract from the rest of the page. cmɢʟee୯ ͡° ̮د ͡° ੭ 11:57, 13 August 2013 (UTC)

It might be useful to have a simpler set of examples of how magnitude relates to linear brightness. I've landed here as a rank amateur simply trying to find out what a magnitude difference (for a rotating asteroid lightcurve) of +/-0.4 means for actual luminance, and I'm still not entirely sure if I've got it right... in fact I've got two different answers, one around +/-0.832x the base figure, the other (more likely) of +/-0.692x. Something basic like what an 0.1 and 0.25 magnitude difference means alongside the 0.5, 1.0 and greater differences already noted (which don't seem to agree?!) as well as a straightforward method of working one to the other in both directions using a regular scientific calculator rather than some kind of advanced graphing model or scientific maths software package (how do you do log₁₀₀ using Windows Calculator or a Casio FX-85? I've no idea... they just have basic "log" buttons that could mean anything) might do the trick...? This information is, after all, of use and interest to absolute beginners with an interest in astronomy, as well as doctors and professors of the art. 146.199.60.87 (talk) 18:29, 11 August 2019 (UTC)

Edit: or from a further reading of another part of the article, it could be simply described in terms of raising 2.512 to the power of the magnitude in question. EG, 2.512 ^ (-)0.4 = 1.445x (or 0.692x) ((to 3dp / 3.5sf, anyway)). For some reason that simple method isn't part of the discussion anywhere else. Though now I'm having difficulty figuring out how to reverse that to get a magnitude from the linear difference...?! 146.199.60.87 (talk) 19:08, 11 August 2019 (UTC)

Edit 2: Never mind, I'm being dumb / have a poor memory / may have had the calculator overlapping important parts of the screen. Simple terms, raise 100 to the power of (difference/5) to get the magnitude, and raise 2.511886... (ie, 100^0.2) to the power of the magnitude to get the difference. Sorted. Though it may still be worth putting that in such simple plain-English terms in the article because the formulae are rather offputting and not immediately comprehensible to the layman... 146.199.60.87 (talk) 19:16, 11 August 2019 (UTC)

2.512, or however many decimal points you want, is an approximation. You will certainly see it discussed in many places, but there are simple ways to calculate magnitude/brightness differences that don't need any approximations. Not to mention that raising 10 to the power of something has to be a better idea than raising 2.512(...) to the power of something. The article doesn't seem to do itself any favours with explanations that seem to favour factoids for maths geeks over simple explanations for the average reader. Lithopsian (talk) 19:40, 11 August 2019 (UTC)

BTW, in my in-my-head fashion, your calculation would be 10^±0.4/2.5. Note that the result is not ± 0.692, but 0.692 or 1/0.692. Lithopsian (talk) 19:45, 11 August 2019 (UTC)

Superbolide

Since a superbolide, as in a very bright meteor, or a "superbolid meteor", is defined as a bolide of high apparent magnitude (see Wiktionary on "superbolide"), I wonder if anyone has a scholarly source for at what magnitude a bolide is no longer a bolide and becomes a superbolide? Need it be brighter than the Sun? (App. Mag. approx. equal to -26) Or what? N2e (talk) 04:40, 21 November 2013 (UTC)

Maybe far too late an update, but the actual superbolide page says "In astronomy, it refers to a fireball about as bright as the full moon, and it is generally considered a synonym for a fireball", and further down the lede says it's usually considered anything of Mag -17 or above, or about 100x as bright as the full moon. So you've still got a bit of a range there, but at least it's been tied down somewhat. 146.199.60.87 (talk) 18:31, 11 August 2019 (UTC)

TZP

I removed a messed up part of a sentence. One part of what I removed said, "and then switched to using tabulated zero points" but I could find nothing using a Google search but pages that quoted this Wikipedia article. No one but a specially trained astronomer knows what a "tabulated zero points" is. Another part of what I removed was an external http reference, that was a dead link, leading to a page with nothing on it. If you have a reference to "tabulated zero points" and can explain what they are, in plain, non-technical, English, please do. I am really curious. Nick Beeson (talk) 21:25, 24 February 2015 (UTC)

It looks a bit better now; at least, from what's written, although I don't understand the actual methods used or what they mean, I can at least understand that a different method based upon using a certain celestial object as the measurement benchmark for "zero" (so other measurements may come out positive or negative in relation to it) is now preferred in some cases because of how the colour of different objects / the colorimetry of the observing equipment may affect the results. 146.199.60.87 (talk) 19:20, 11 August 2019 (UTC)

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Relation to implied distance

If true, could we note somewhere that 5 magnitudes fainter implies 10 times further away (since it is used in distance modulus) ? - Rod57 (talk) 19:22, 16 January 2017 (UTC)

That would seem self evident given that the inverse square law itself implies something that appears 100x fainter is likely 10x as far away, but it may still be worthy of exposition? 146.199.60.87 (talk) 18:33, 11 August 2019 (UTC)

Faintest object seen by hubble

The cite seems to say limiting magnitude 31.2 - it would help to have a quote for the 31.5 in the footnote, a search of the paper for the number 31.5 turns up a blank. Is it a typo? Robert Walker (talk) 10:01, 20 May 2018 (UTC)

Main Article Problems

There are many problems with this article page that need significant improvements or update. Fixes include:

• Magnitude is a unit of measure of relative brightness.
• The value is not dependant by observations from Earth. e.g. Planets still can have a different apparent magnitudes when viewed, say from Mars. It is the observer perspective not necessiarily from Earth
• Apparent magnitude often is taken to mean apparent visual magnitude - specifically visible light seen by the human eye.
• Apparent visual magnitude uses 'v' e.g. 4.5v with instrumental means like photometry uses 4.5V, etc.
• There is no mention of photometric magnitude (different from visual magnitude and notable requires conversion from on system to another) Nor under Magnitude (astronomy) or Photometric system
• Various contradictions with Magnitude (astronomy) or Photometric system (Main Strömgren photometric system (related to stellar classification isn't mentioned.
• Added text also showing positive magnitudes, and exampled range of possible magnitudes with cite.
• Added the definition of unit of brightness, based on the apparent bolometric magnitude. This has a value of energy measure in watts per square metre (which is measured with a bolometer), where apparent standard is a 0.0 magnitude star. A source for this is "IAU 2015 Resolution B2 on Recommended Zero Points for the Absolute and Apparent Bolometric Magnitude" [1]

I have attempted an improvement in the Introduction, but from the fragmentary nature of the article's text is near impossible to repair.

History section

The History section is very confusing and is poorly cited. Various contradictions appear with Magnitude (astronomy)#History

• Vega as a standard 0.0 magnitude is sometimes used for instrument calibrations (There are other ways e,g, Described here[2]) How is this used in the southern hemisphere where Vega isn't visible or has intinction problems?
• It says "The brightest stars in the night sky were said to be of first magnitude" The link to brightest stars is irrelevant, and only refers to stars above 1.0 (or 1.25 in some sources or 1.5 magnitude under Magnitude (astronomy))
• A second paragraph should have something written about visual estimates of the brightness of stars made with the naked eye. These appear in older text books/ Some of these in the early 19th Century used comparison photometry. Magnitudes of such stars have 'v' attached. I.e. 3.5v.
• There is little explanation to why surface temperature is related magnitude (It should be linked to the article on luminosity) Most of the text around Vega should probably be removed. The last paragraph has been mostly superseded and might be rightfully removed.
• Energy is related to Wien curves
• Variable star observers can estimate magnitudes to 0.11 magnitude and visual observers to about 0.3 magnitude
• There is no mention of atmospheric extinction

Absolute magnitude section

Most of this should be simplified, summarised and condensed. It should plainly mention that apparent magnitude is independent of distance, while absolute magnitude is based on an arbitrarily set distance of 10 parsec.

• I could not find the source of this statement: "Indeed, some L and T class stars have an estimated magnitude of well over 100, because they emit extremely little visible light, but are strongest in infrared."
• The article mentions photographic magnitude, but there is not mention how this related apparent magnitudes.
• The part about the Milky Way absolute magnitudes and redshifts or there correction appears irrelevant to the article.

Table of examples

Most of this listing is theoretical and difficult to understand. Suggest making a shorter Table with atypical values for bright star and planets. he labels should b changed from "planet Mercury" to Mercury (planet) which would make this more readable. (or even a separate column?)

NOTE: @Lithopsian: There also needs to be an explanation of usage. Many articles have odd usage, like "magnitude 6.0" or or a " the components are magnitudes 4.0 and 5.1 respectively"[3] If magnitude is the unit measure of brightness, then the value must be followed by the unit measure. e.g, "6th magnitude' or "6.0v magnitude" or a "double star is 4.5v and 5.6v magnitude" must be correct. Using the plural of magnitude is also incorrect usage in this respect. Better usage would be "magnitude of 6.0" I find few examples of the reverse usage in the popular or astronomical literature. The claim "correct usage of magnitude as a unit," must be problematic? RfC??

This is explained here[4], where the IAUえーゆー officially says: "5.17 Magnitude: The concept of apparent and absolute magnitude in connection with the brightness or luminosity of a star or other astronomical object will continue to be used in astronomy even though it is difficult to relate the scales of magnitude to photometric measures in the SI system. Magnitude, being the logarithm of a ratio, is to be regarded as a dimensionless quantity; the name may be abbreviated to mag without a full stop, and it should be written after the number.." Also it says: "The use of a superscript m is not recommended. The method of determination of a magnitude or its wavelength range may be indicated by appropriate letters in italic type as in U, B, V. The photometric system used should be clearly specified when precise magnitudes are given."

Arianewiki1 (talk) 08:27, 19 May 2019 (UTC)

Standard reference values section

The one thing that the Standard reference values section doesn't seem to discuss is standard reference values, although there is a table of standard fluxes in various passbands. The text of the section is just general chit-chat, very poorly-referenced. I can't think of a name for it. Should it just be dumped and written from scratch? Chopped up and farmed out to other places like the history section? Lithopsian (talk) 19:26, 7 June 2019 (UTC)

Agreed, it's a bit of a mess. It seems to be a general discussion of the difficulty and caveats involved in using a single magnitude value, or one biased towards a certain limited set of spectral bands, to describe all celestial objects; essentially it's just mistitled. The table is more in line with the title as is, but it's also pretty confusing (I recognise almost none of the units used, and I'm not sure why we can't just use watts or lux/lumen), and the only columns that seem to be directly relevant are the first (band designation) and one or other of the last two (luminous flux that's equal to zero magnitude in that particular band); the others could probably be dumped and just replaced with a link to an article about astronomical spectral bands, if one exists. 146.199.60.87 (talk) 19:27, 11 August 2019 (UTC)

Pre-photometric methods of determining magnitude...

The article mentions that magnitude determination was crude and subjective before the invention of photodetectors, but I do wonder if there would be a way of classifying things in a repeatable fashion to a certain arbitrary level of precision - say, 0.1 on a log2 scale? (Which would give us less than 100 steps from "too faint to see" up to "brightest known object other than the sun and moon", and it's entirely possible to rank printed or on-screen greyscales more finely than that, by eye, so long as you can compare between them, and the dynamic brightness of a VDU or piece of paper is far less than that of natural light)

There are various methods I could think of... for example, the earliest hour that a star becomes visible after sunset, especially if you make repeat measurements at the summer and/or winter solstice and equinoxes, using some way of excluding visual pollution from the horizon or nearby dwellings (e.g. the classic lensless paper tube "telescope", or the makeshift observatory of a building missing its roof - the latter of which, along with a parabolic support made of bricks, was something actually used by pre-optical-glass astronomers, especially in Arabia). Date and time was something much more easily measured even in antiquity, and the motion of the stars and planets themselves was used to measure such. Your determination could then be checked by seeing whether certain well known benchmark stars were or were not yet visible, and a ranked list drawn up and refined over time. Once you had sufficient entries, it would be enough to simply wait for the first moment the star / planet of interest became visible, and quickly check to see which other stars off the list in the general predicted neighbourhood were already visible, in order to add the as-yet unranked one into the catalogue in the right place...

Maybe it wouldn't be absolutely accurate, or mathematically precise other than in terms of direct comparison, but for the type of astronomy that was even possible (and thought relating to it) in the pre-telescopic age, it would likely have been more than sufficient, and still fairly scientifically valid. Astronomers of old weren't entirely stupid, after all, just limited in the equipment they had available. It's not beyond the realm of imagination to consider they might have come up with some clever scheme to repeatably determine the objective brightness of a star (after all, I just pulled one out of my ass, and I haven't had a lifetime of pondering on the meaning of the universe in an age long before multichannel TV and the internet); the brightening and darkening of the sky, on clear nights, in an age before any meaningful atmospheric or indeed much light pollution, would have been like the apocryphal clockwork, and something you could set your biological photometer by. 146.199.60.87 (talk) 19:41, 11 August 2019 (UTC)

And? None of this can go in the article without reliable references. However, when you've published your phD thesis on the subject ... :) Lithopsian (talk) 19:47, 11 August 2019 (UTC)

Logarithmic or reverse?

@Lithopsian: Your last edit was a valiant attempt, but now you have "The magnitude scale is logarithmic..." while the next sentence begins "The magnitude scale is reverse logarithmic...". Your comment "not entirely convinced it is better" is well said :) Definitely a tough topic to introduce without confusing people. Might've been better to just revert the unregistered user's edit; what was there before was much clearer, in my opinion. Assambrew (talk) 08:19, 16 October 2020 (UTC)

I agree, obviously, but I thought there was some merit to the intent of the IP edit if not the grammar. I've changed it back, although I still think it could be improved. The wording was contentious when it was added, but seemed to be the best that several editors could come up with at the time. I made a couple of very small changes, hopefully improvements. Lithopsian (talk) 13:20, 16 October 2020 (UTC)

Thanks. Yes, the IP edit was a valiant attempt as well. The 2nd paragraph of the Magnitude (astronomy) article is another try. Starting out with the math probably loses people; somewhere in the intro should be said that the scale was defined as a way to match the ancient historical system. Something like that anyway.

I re-added Polaris to the "List of apparent magnitudes"; I had added the other day, but it got reverted when you did your thing. No problem, I asked for it :) Assambrew (talk) 18:39, 16 October 2020 (UTC)

I added historical precedent before the math; figured the reader needed a reference point before diving in. Also modified the following paragraph some, didn't think it needed "100 times" twice. Assambrew (talk) 07:02, 19 October 2020 (UTC)

Discussion of apparent brightness

Just noticed that "apparent brightness," though redirecting here, isn't talked about at all, although the article seems to use it to mean something specific. Perhaps it could be brought up (or removed)? –LogStar100 (talk) 19:24, 3 February 2021 (UTC)

Good spot, but I wouldn't want to use this term in the article. It would add confusion. "Apparent magnitude" is a defined scale (if not quite a unit), whereas "apparent brightness" is an adjective and a noun. If you think the redirect is bad enough not to exist at all, that would be addressed at WP:RFC although I suspect it would fail. Or find a better place to point the redirect. However, there are quite a few articles that link to it. I've edited half a dozen and dare say the rest should be changed because it is sloppy and in some cases misleading to use this wording. Hipparcos may be the worst offender, discussing "apparent brightness" and "intrinsic brightness" in a very strange way not fully explained or supported by references. I'm not sure what it is trying to say. Might want to take a look at that and see what you think. Lithopsian (talk) 21:07, 3 February 2021 (UTC)

Apparent magnitudes table error

The table "Standard apparent magnitudes and fluxes for typical bands" lists various bands. Jy column at first appears to follow the spectral black body curve, as would be expected, since the units are per Hz, and agnostic of the band width, however the Jy values for bands g,r,i,z are inconsistent with the above bands and appear to be in error.

Mercury maximum brightness at superior conjunction

This seems to me a little bit academic, because when Mercury is at superior conjunction, you can't see it. The same thing goes for the minimum brightness of Mercury (around inferior conjunction). Realistically, the most useful apparent magnitude of Mercury is going to be that around maximum elongation, right? Double sharp (talk) 09:13, 2 October 2021 (UTC)

First table, possible error

The table listing "Number of stars (other than the Sun) brighter than apparent magnitude in the night sky" seems not correct. If the number 9100 is correct, the numbers at the top should also include the magnitude on the respective rows and the stars on rows above, as the number 9100 from Bright Star Catalogue implies. That is, the second row in that column should say 5 rather than 4. (Maybe other lines should also be changed.) Fomalhaut76 (talk) 15:25, 20 March 2023 (UTC)

I suspect that table is correct, at least it matches the given references and my expectations. Someone seems to have misinterpreted the information and added four star names where there should only have been three (plus Sirius). I have removed Vega, which is generally considered (see List of brightest stars) to have an apparent magnitude greater than zero, although it is slightly variable and sometimes brighter than magnitude 0.0. Lithopsian (talk) 19:50, 20 March 2023 (UTC)

Relation to decibel

It is stated that the magnitude scale can be related to the decibel scale, as one magnitude step equals exactly 4 dBでしべる. I can see that this is mathematically correct, but is there anyone actually using decibel in this way? If no source to actual use of decibel related to apparent magnitude, then the statement should be deleted, as it does not convey any useful information. JakobT (talk) 08:13, 9 August 2023 (UTC)

Jupiter seen from its moons

It would be great if someone could add into the list the apparent magnitudes of Jupiter when seen from certain moons, a "full Jupiter" e.g. from Metis, the Galilean moons or Himalia. 2001:4BC9:1F98:112C:B897:9213:2412:1F13 (talk) 17:07, 8 October 2023 (UTC)

Historical inaccuracies

Hi! Both this page and Magnitude (astronomy) claim that Pogson defined magnitude zero to be based on Polaris = 2.0, and then astronomers switched to Vega = magnitude 0.0. I was curious about the history of magnitude, and fell down a rabbit hole of research, and then an wrote an article called The Cursed History of Star Brightness [5] about my findings: I tracked down Pogson's original paper, and it actually defined magnitude 6.0. In fact, this page's history of magnitude section contains some errors in the large citation-free paragraphs.

Magnitude (astronomy) makes the same claim that astronomers defined magnitudes using Vega = 0.0, but cites page 182 of a book. That book, as seen on https://books.google.com/books?id=Ps_6zjUCR3wC&q=182#v=snippet&q=182&f=false here, does mention Vega's variability several pages after page 182, but it describes a model for the spectrum of Vega from 1991, far after Johnson's system was invented, and doesn't say that the model is used to calibrate magnitude zero.

This page also claimed that "Therefore, the magnitude scale was extrapolated to all wavelengths on the basis of the black-body radiation curve for an ideal stellar surface at 11000 K uncontaminated by circumstellar radiation". It cites https://archive.today/20121204144725/http://www.astro.utoronto.ca/~patton/astro/mags.html, but that website doesn't mention anything about a black body spectrum. I've removed it in my edit, but if anyone does have a source for that claim I'd love to see it.

Since I found many primary sources while doing research for my article, I've edited this page to reflect what I understand is the correct history. If any of you Wikipedia editors have any comments, suggestions on how to rewrite it, or sources about the history of magnitude, please let me know! Explanaria (talk) 20:28, 23 May 2024 (UTC)

Total visual magnitude v. Apparent magnitude

This edit by made Aldebarium here [6] I believe might be incorrect because it is mixing up what is termed as total visual magnitude with apparent magnitude. The former is the true visual magnitude regardless of interstellar absorption or atmosphere - more properly termed as air mass or extinction if taking into other factors like Rayleigh scattering, air-pollution, ozone or aerosols, etc.

For example, if a 1.0 magnitude star is observed zenith, total visual magnitude and apparent magnitude are almost the same. (Extinction averaging about -0.16 [7] A true value is more complex.) If the same star is observed near the horizon, the total visual magnitude would be 1.0, but the apparent magnitude would be less, say about 1.8 magnitude when 30° above the horizon.

Apparent magnitude is simply how bright an object appears to the naked eye and is dependent of other factors. Defining the total visual magnitude these other factors must be taken into account. I.e. Two observers on the ground separated my great distance will see starlight with two different apparent magnitudes, even though the star has exactly the same total visual magnitude.

The sentence: "Its value depends on its intrinsic luminosity, its distance, and any extinction of the object's light caused by interstellar dust or atmosphere along the line of sight to the observer." is correct. Itchycoocoo (talk) 02:43, 8 August 2024 (UTC)

I’m not sure where you’re getting this information from, but the way you’ve defined apparent magnitude is not correct, and is not consistent with how astronomers use the term. A star’s apparent magnitude is not simply how bright it appears to the eye when observed under differering atmospheric conditions. It is a well-defined physical quantity that is measured in a way that is corrected for atmospheric extinction, so that all astronomers can agree on what the apparent magnitude of a particular star is in a given filter band, regardless of whether they observe it through different airmasses or from different locations that have different atmospheric extinction. (Here’s a review paper that is a thorough reference on this topic.) In practice apparent magnitudes are calibrated using observations of standard stars whose apparent magnitudes have been well-determined, such as standard stars from the Landolt catalog, or stars listed in the APASS catalog. If apparent magnitude was different every time you observed a star under different atmospheric conditions, these tables would have no useful meaning at all. Just to give a concrete example: you can look up the properties of the star Feige 34 in the SIMBAD catalog, and SIMBAD will tell you that it has a magnitude in the V band equal to 11.14. That’s not dependent on the atmospheric conditions under which it is observed- that is just the apparent magnitude of that star in the V band, plain and simple. Additionally, the term “total visual magnitude” isn’t used in astronomical literature in the way you’re using it. “Total visual magnitude” can be used for comet measurements to denote the total brightness over the full extent of a comet as opposed to just the brightness of the comet’s nucleus, or it is sometime used to denote the total magnitude of other kinds of spatially extended objects such as galaxies over the full extent of the object. This is very different from how you’re using the term. Aldebarium (talk) 23:52, 12 August 2024 (UTC)

Aldebarium You say: "A star’s apparent magnitude is not simply how bright it appears to the eye when observed under differing atmospheric conditions. It is a well-defined physical quantity."

Sorry. Apparent magnitude does no equal visual magnitude. "Apparent magnitude is a measure of how bright a celestial body appears to an observer... The common "visual magnitude" scale is set so that the bright star Vega has an apparent magnitude of zero." See [8] A good guide is: the Oxford reference, which quotes: "the apparent magnitude of a star as estimated by the human eye."

If I look at Vega, it's apparent magnitude varies depending on both the atmosphere, more accurately air mass, and the interstellar extinction caused by material lying between us and the star. When we say that Vega is 0.0 magnitude, we are saying that the brightness of the star has a visual magnitude. If we look at Vega, say when it several degrees above the horizon, its apparent magnitude is fainter but it's true visual magnitude is unchanging.

When we talk about stars, we often use it in terms of comparison to other stars, and we assume we are in observer looking at them from space. Laziness, or traditionally the way we talk about brightness of stars, means we're not really interested taking into account the dimming of the Starlight. We are only interested in comparison. A good example are double stars. Before accurate photometry, new double stars when they discovered them near to the horizon often have seemingly lower magnitudes then instrumental measures. The reason is simple, as they estimated pair's brightnesses by eye and not accounting for the atmosphere, etc.

Transformation of magnitude are particular difficult, and is often is applied in variable star research. An interesting pdf article is here [9] Quoted magnitudes rely on using standard stars to calibrate Instruments to measure magnitude. The standard stars have already taken into account the observing conditions, and therefore, could be referred as total visual magnitude. I.e. Magnitudes did have the interfering factors removed. The magnitudes, say in SIMBAD, as you point out, rely on complex calibration of photometric equipment.

Let's look at another way.

If I observe a star close to the horizon and estimate how bright it is, how do I describe its brightness/magnitude? What is the definition of that?

Lastly, what you're saying about extended objects is absolutely true. I have no disagreement with you on that point. Itchycoocoo (talk) 06:57, 14 August 2024 (UTC)

This explains it. "visual magnitude. (mv) The apparent magnitude of a star as estimated by the human eye. The eye is capable of ranking stars in order of brightness and estimating equality between two stars, or a star and an artificial source. These were the only ways to measure visual magnitudes until the advent of the photovisual magnitude." [10] Itchycoocoo (talk) 07:08, 14 August 2024 (UTC)