Talk:Canopus

Tidy-up

I added the detail of the star's ancient role as a 'southern pole-star', and turned the mention of Canopus in Argos into a working link. I also created subheaders and moved a couple of paragraphs to a more logical order.

--GwydionM 19:20, 17 January 2006 (UTC)

Discussion of fiction has been moved to Stars and planetary systems in fiction --GwydionM 17:56, 13 November 2006 (UTC)

"About 90,000 years ago, Sirius moved close enough that it became brighter than Canopus, and that will remain the case for another 210,000 years. But in 480,000 years, Canopus will once again be the brightest" - so what happens between 210k AD and 480k AD? — Preceding unsigned comment added by 92.14.30.2 (talk) 23:52, 5 March 2012 (UTC)

Frank Herbert's Arrakis?

Is identification of Canopus as the Arrakis in Frank Herbert's Dune correct, from the text of the novel itself? Arrakis is one form of the Arabic name for Mu Draconis, HR 6370. BSVulturis 22:06, 19 September 2006 (UTC)

Colour

Canopus is not "yellowish white". It's a white star. Look at the photo included--white with a tinge of blue. —Preceding unsigned comment added by 192.30.202.20 (talk) 21:32, 23 November 2007 (UTC)

Erm not necessarily a true colour photo but...thought I'd try and clear this up...an IP changed the Canopus page to describe it as a white rather than yellow-white star. I changed back as that was what I always read in books as a kis but thought this was what was meant so worte it thus to clarify. Is this an accurate appraisal, and if so can we get a ref for it? I am still a neophyte at star stuff. cheers, Casliber (talk · contribs) 12:46, 13 December 2007 (UTC)

Canopus is a F-class supergiant star and essentially white when seen with the naked eye, though these stars are considered to be yellowish-white when viewed in greater detail.

The terms yellow and yellow-white are constructs and are used in reference to Vega, a sort of stellar 'white standard'. Yet Vega, A0V, is blue-white to the eye. The photo of Canopus here looks true-colour to me, unless that camera was heavily biased to the red. Even 'red giant' stars like Aldebaran really look yellow-orange. 68Kustom (talk) 10:03, 10 February 2008 (UTC)

Remember the stars colour was first examined by using a spectrum. The colours are O(blue) B(blue-white) A(white) F(yellow-white) G(yellow) K(orange) M(red), or Oh Be A Fine Girl and Kiss Me! Canopus is and F type star (yellow-white) while our Sun is a G(yellow). —Preceding unsigned comment added by 125.254.66.213 (talk) 05:27, 5 July 2008 (UTC)

Units of angle

this is based on a parallax measurement of 10.43 ± 0.53 mas.

Would it be unreasonable of me to edit this by inserting "about 5 nanoradians" in parentheses at the end of the sentence, like so?

this is based on a parallax measurement of 10.43 ± 0.53 mas (about 5 nrad).

--arkuat (talk) 04:33, 8 June 2008 (UTC)

Accurate, perhaps, but irrelevant – astronomers do not measure parallaxes in nanoradians but in mas, as correctly quoted at present. Skeptic2 (talk) 07:23, 5 July 2008 (UTC)

Just how big is Canopus again?

The article says Canopus is 65 times the size that of the sun and yet latter says that if placed in our solar system it would only come out to three quarters to Mercury's orbit. Those two things seem to conflict with each other. Mercury is very close to the sun. How can Canopus be 65 times the size of the sun and yet would only not envelop the inner planets?

--69.37.140.100 (talk) 01:01, 8 February 2009 (UTC)

This isn't the only problem with the article. I agree with the OP regarding the size given as 65x Sol or 0.6 AU which would engulf Mercury and have Venus skimming over it's surface. Earlier in the same section it states "...distance estimates for the star varied widely, from 96 light years to 1200 light years. Had the latter distance been correct, Canopus would have been one of the most luminous stars in our galaxy." The "latter distance" is 1200 ly which is further than the article states it's distance is now, it should imply that if the star was only 96 ly it would be the most luminous. — Preceding unsigned comment added by 207.255.204.36 (talk) 08:05, 7 October 2011 (UTC)

You misunderstand: the text refers to its intrinsic luminosity, not to its apparent brightness. For a given AB, the further away it is, the higher its IL. --92.14.30.2 (talk) 23:52, 5 March 2012 (UTC)

(signature above added for future reference) The diameter of the sun is 1.392 million km, let's say 1.4 million to keep it simple. 65 times that would be 91 million km, and the radius would be 45, just inside the orbit of Mercury. Part of the problem lies in the eccentricity of Mercury's orbit; the aphelion (farthest from the sun) is about 1.5 times the perihelion (closest) distance, which is about 46 million km.

Bottom line: Mercury is much closer to the sun but not that close. - ¡Ouch! (^{hurt me} / _{more pain}) 13:31, 12 January 2018 (UTC)

Chinese name

In the paragraph Etymology, Canopus appears to be known as Laorenxing in Chinese. I find this surprising as, to my knowledge, the sound "r" is not present in chinese language. Has this been checked by some chinese mother tongue expert?--Franco3450 (talk) 14:41, 9 April 2009 (UTC)

The usual transliteration is simply Laoren. Skeptic2 (talk) 15:27, 9 April 2009 (UTC)

"Laorenxing" is simply the Pinyin romanization, which uses "r" to express the retroflex approximant. We didn't use to see "r" in romanization of Chinese, since Wade–Giles, the most common system before Pinyin, didn't use that letter, employing "j" instead for the same sound. ◄ Sebastian 13:43, 12 February 2019 (UTC)

Visibility

In an effort to make the section on the visibility of this star more universal, I chose to show a location from which Canopus would not be visible (Richmond, Virginia) and one in which it would be visible (Atlanta). Many people in the eastern USA don't realize how far south San Francisco is... but they realize well enough how far south Richmond and Atlanta are.

Thanks - I think this would be useful. What is needed though is some sourcing. Can you get some from an american star observation book or something? Cheers, Casliber (talk · contribs) 04:12, 8 August 2011 (UTC)

Universal? Really? This is absurdly American-centric. — Preceding unsigned comment added by 92.14.30.2 (talk) 23:54, 5 March 2012 (UTC)

Well, then edit it to include points of reference that are outside the USA, rather the gripe because Americans did most of the work on the article and used points of reference familiar to them. 71.49.46.224 (talk) 13:49, 1 June 2012 (UTC)

Stellar evolution – dubious statement

About 90,000 years ago, Sirius moved close enough that it became brighter than Canopus, and that will remain the case for another 210,000 years. But in 480,000 years, Canopus will once again be the brightest, and will remain so for a period of about 510,000 years.
I read this in the article and seriously doubt if it is something we can say with 100 percent certainty. Canopus is so massive that it evolves very quickly, and may not exist in its current form in half a million years, especially considering that it is already off the main sequence. Statements like this should really have a verifiable source. 71.49.46.224 (talk) 13:49, 1 June 2012 (UTC)

Nothing to do with evolution (and even if it was, we can state "most likely" or "consensus" scientific opinions "as fact"), the timescales are much too short for that. This change is simply due to the movement of the stars, becoming closer to or further away from us. Lithopsian (talk) 15:15, 21 April 2019 (UTC)

Greeks and Argo Navis

If the star wasn't visible to the Greeks, how did it become associated with Argo Navis before the Age of Discovery? 137.205.120.187 (talk) 16:45, 11 November 2013 (UTC)

Ptolemy and other ancient Greek astronomers observed it from Egypt (Alexandria) which is a couple of degrees further south than Athens and put the star within reach. Alexandria was largely a Greek city. I agree it should be pointed out more clearly in the article though. The text discusses the names of this star in lots of different cultures around the world but fails to make it clear when and how it was actually given the name Canopus in classical and western astronomy. 83.251.170.27 (talk) 17:38, 7 December 2015 (UTC)

Good point...now to find a good ref for it....Cas Liber (talk · contribs) 23:40, 7 December 2015 (UTC)

Eratosthenes first used the name Canopus for this star in his Catasterisms. He also called it Perigeios because not star is visible closer to the horizon. http://www.ianridpath.com/startales/carina.htm 148.122.163.70 (talk) 19:31, 9 December 2015 (UTC)

move to Canopus (star)

Name of star < name of ancient port < name of mythological pilot. And I don't see how the star is the most notable of all. The lemma Canopus should lead to the disambig.--94.68.128.29 (talk) 09:20, 4 November 2015 (UTC)

Disagree - the star is by far and away the most notable object in modern parlance. Cas Liber (talk · contribs) 09:22, 4 November 2015 (UTC)== move to Canopus (star) ==

The star is by far the most notable. It actually exists, in the present day. It is bright enough for billions of people to think to ask its name, and well known enough for tens of millions of people to give the correct answer.At least I try (talk) 11:33, 5 May 2016 (UTC)

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Spectral class?

The article references Lopez (1993), page 66 and gives the spectral class as A9 II; the also referenced Cruzalebes (2013), p. 12 gives F0 II (both in infobox); but the Hiparcos catalogue (1997) gives it as F0 Ib ([1] ). What is it? At least the values should agree with referenced sources. Kipala (talk) 12:41, 31 December 2017 (UTC)

The article agrees with the referenced source (actually Lopez-Cruz, all one person, also Gray & Garrison, 1989), you said so yourself. Cruzalebes just copies an older value, so ignore it. Hipparcos is not a spectral reference source, I'll leave it up to you to trace where they got their old data from. Historically, F0II is an aberration, as described in Houk (1978). A9II is also somewhat unusual, with F0 and a supergiant luminosity class being most common before 1989, but A9II is the most recent determination of an MK spectral class. The change is mainly due to a redetermination of the MK standards for "early F" stars (Gray & Garrison, 1989), as confirmed by Lopez-Cruz (1993). Anything else you may think you see is either a hallucination or rote copying of older values. Lithopsian (talk) 14:46, 31 December 2017 (UTC)

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What else?

I'm running short of (referenced) things to add to the article. Either I'm not looking hard enough or there isn't a lot else out there. It would be nice to write some more about evolution, but I can't find references that discuss it. It is probably a super-AGB star, although has also been considered as a low-mass supergiant. Its evolution is balanced between becoming an exotic type of white dwarf or an unusual type of supernova, but not many people are going on paper to discuss it. Lithopsian (talk) 11:41, 24 May 2020 (UTC)

Periodically I've looked at this one over the years and been surprised (and stymied) by the lack of information. And given up. The main eyesore is all the cultural/historical stuff at the bottom of the article, which is disjointed and needs to be tidied up and coalesced into paragraphs. We could flesh it out a little by adding the 1997 parallax just to give a sequential estimate of distance over time. Also - if we could add anything to the evolution section - e.g. how long is a blue loop? (funny to think it has alrready been a red giant...). Also (I might be imagining this)...did I read somewhere a discussion about its position relative to the instability strip and was it odd that it did'nt pulsate more...? Cas Liber (talk · contribs) 22:03, 24 May 2020 (UTC)

The other headache is where to slice and dice all this historical/cultural content. Some of it is about observational history, so could go in observation section, but then we have (say) polynesian and chinese material scattered in two different sections...or just hive off all historical stuff down the bottom in cultural section. Other issue is that alot of Richard Hinckley Allen's material is...not so much dubious as.....better checked against more rigorously researched material. Cas Liber (talk · contribs) 00:04, 28 May 2020 (UTC)

I think the Observation section is the problem, and the rest of it is probably OK where it is. Some of it is just description, called "Visibility" in some other articles, plus a few random observations. None of it really forms a historical narrative. That section should probably be dismantled. Maybe we still want a section giving a history of modern observations? Maybe not really necessary as a star known and named since ancient times, as covered in the Nomenclature section. Lithopsian (talk) 10:28, 29 May 2020 (UTC)

I have added this paper, which even suspects in 1981 that it might have passed through a red (super)giant phase even then. Cas Liber (talk · contribs) 09:55, 29 May 2020 (UTC)

Good find. Just the sort of information I was looking for. Lithopsian (talk) 10:20, 29 May 2020 (UTC)

I was also thinking of adding how the parameters (such as mass) were derived from the angular diameter but couldn't figure a good way of phrasing it. I think it would benefit from expansion of how we ended up with different spectral types. I guess illustrating how properties are calculated rather than just presenting them as fact. Cas Liber (talk · contribs) 11:08, 29 May 2020 (UTC)

Yes, I'll expand a bit on the derivation of mass and other properties. The spectral type thing is going to be harder to explain clearly and simply; it feels like a huge difference between A9II and F0Ib but really it isn't. Maybe I can present a little more of the history of these changes, especially since the reference we have doesn't do a good job on it. Lithopsian (talk) 21:06, 29 May 2020 (UTC)

A paper from 2017 here uses F0II as spectrum for Canopus. A paper from 2015 does as well, referencing Greenstein 1948. Cas Liber (talk · contribs) 23:43, 1 June 2020 (UTC)

Astronomers can be pretty sloppy. Referencing the Bright Star Catalogue (which was probably the same spectral type that Simbad showed at the time) is understandable and common, but why on earth would you pull an obscure 1948 paper out of nowhere? The paper does answer that: "We generally report the oldest classification(s) consistent with subsequent papers, except where improved classifications are available ...", but it doesn't seem to regard Gray and Garrison (1989) as being an improved classification. The following recent journal papers, as well as Simbad, adopt A9II: Bourges et al. (2014-2017), Cruzalebes et al (2019), XHIP, and et al. (2011), but F0II and F0Ib are still commonly seen, perhaps a little less in the last decade or so. F0-something is almost universal if you go back before about 1990, and in most books. I also found a paper giving F0 III, not sure if that was a typo. I usually pick whatever Simbad goes with, occasionally something like the GCVS when it seems to give a more holistic view for a particular star. Lithopsian (talk) 15:27, 2 June 2020 (UTC)

I thought it was fascinating how rarely it was studied - probably because of its location and hence inaccessibility to many northern hemisphere observers. I think SIMBAD generally does go by consensus and tries to gage the strength of the material. Cas Liber (talk · contribs) 00:55, 4 June 2020 (UTC)

Fascinating and frustrating. Do you think we need to describe the spectral class thing differently? Another source I like to look at is Skiff (2009-). A handy history of MK-style spectral type when the Simbad one looks a little off. Lithopsian (talk) 12:16, 4 June 2020 (UTC)

That source is rolling with F0I from.....1932?? Cas Liber (talk · contribs) 14:39, 7 June 2020 (UTC)

Its a list, ordered by date. Lithopsian (talk) 14:51, 7 June 2020 (UTC)

But yes, I think expanding on how spectra are analysed is good - almost worth having a footnote that A9 and F0 are right next to each other as well...but would that be OR.... Cas Liber (talk · contribs) 23:14, 7 June 2020 (UTC)

@Lithopsian:, isn't Canopus on warm side not cool side of instability strip? Cas Liber (talk · contribs) 21:16, 13 June 2020 (UTC)

Just checking to see if you were paying attention :) Lithopsian (talk) 19:06, 14 June 2020 (UTC)

I can't find anything else on time scale of blue loops annoyingly..... shall we just nominate it at GAN as otherwise fairly complete? Cas Liber (talk · contribs) 12:54, 16 June 2020 (UTC)

Blue loops for intermediate-mass stars are a few million years, 10-20% of the main-sequence lifetime for this mass range, but highly dependant on initial mass, rotation, and even the details of the model. I don't think you're going to find anything specific to Canopus. This paper is a slightly old overview of blue loops. It gives 6 MYr as a typical length of the blue loop for a 7 M_☉ star (would be a little less for Canopus), but it also talks about how sensitive this is many factors. Lithopsian (talk) 14:16, 16 June 2020 (UTC)

@Lithopsian: do you think we can use this or is it a bit too off-topic? Cas Liber (talk · contribs) 21:44, 4 September 2020 (UTC)

Also - the bit about precession and it, Achernar and the south celestial pole need a rewrite and better/reliable sourcing. Anything else? Cas Liber (talk · contribs) 21:44, 4 September 2020 (UTC) @Lithopsian: - one thing that might be good is what exactly it is about the spectrum that tells us it's already been a RSG and is in a blue loop....(?) Cas Liber (talk · contribs) 22:19, 4 September 2020 (UTC)

Also this paper already used (gives the high abs mag value in infobox). Helps explain (later outdated) view that it is 15000 times as luminous as the Sun. Cas Liber (talk · contribs) 14:04, 5 September 2020 (UTC)

A long paragraph I'd like to trim.

The Observation section of the article contains this paragraph (which I've already trimmed):

Seen from latitudes south of 37° 18′ S, Canopus is a circumpolar star. Since Canopus is so far south in the sky, it never rises in mid- to far-northern latitudes; in theory the northern limit of visibility is latitude 37° 18′ north. This is just south of Athens, Richmond, Virginia (USA), and San Francisco, and very close to Seville and Agrigento. It is almost exactly the latitude of Lick Observatory on Mt. Hamilton, California, from which it is readily visible because of the effects of elevation and atmospheric refraction, which add another degree to its apparent altitude. Under ideal conditions, it can be spotted as far north as latitude 37° 31′ from the Pacific coast.[21] Another northernmost record of visibility came from Mount Nemrut in Turkey, latitude 37° 59′.[22] It is more easily visible in places such as the Gulf Coast and Florida, and the island of Crete (Greece) where the best season for viewing it around 9 p.m. is during late January and early February.[19] Canopus is also visible from India, but in North India (36° 13′) can be seen near the horizon, while in Southern India it can be seen without difficulty high above the horizon (08° 04′).

Is this interesting or not? I don't think this content is worthy of such a long paragraph, but what do others think? Attic Salt (talk) 03:05, 30 May 2020 (UTC)

Who's to say? Might be interesting to some people. Must have been interesting enough for someone to write in the first place. It seems to have reasonable references. I'd say leave it and just try to structure things so it isn't getting in the way of other things. I've moved some stuff out of the Observation section and it probably should be renamed now, but maybe more tidy-up needed. Lithopsian (talk) 20:43, 30 May 2020 (UTC)

I think (given it's teh second brightest star in the sky) alot of folks around those latitudes think it is a big deal - it could be tidied though. IIRC I added the Nemrut bit as I thought that was cool. I remember Patrick Moore's books also making a big deal about what could be seen from where (e.g. Ursa Major being v low on northern horizon for us in Oz) and what was/is circumpolar. (I did remove on unreferenced line that stated the obvious about observations from India. Cas Liber (talk · contribs) 23:16, 30 May 2020 (UTC)

Pulsations

Thanks for asking me to join :-) My eye was caught by the sentence "Canopus pulsates slightly with a period of 6.9 d. " I have not been able to find any papers to confirm this. Those old radial velocity variation from 1906 are probably not worth mentioning. By the way, RV variations can have other causes so if you do keep the reference, I would replace "pulsates" by "varies". Timb66 (talk) 07:00, 15 June 2020 (UTC)

Thanks for the input! @Lithopsian: what do you think? Cas Liber (talk · contribs) 02:26, 16 June 2020 (UTC)

The RV variations have been measured more recently. I mentioned the old paper as a historical anecdote. It was common back then to describe orbits based on RV measurements like these. The second reference describes some of the newer measurements and mentions pulsations. It doesn't exactly say what is producing the radial velocity changes though. I'll try to reword this a little more vaguely unless I can find something else about it. Lithopsian (talk) 09:25, 16 June 2020 (UTC)

That sounds good to add. Cas Liber (talk · contribs) 12:53, 16 June 2020 (UTC)

name mess

Actually the whole name bit needs an overhaul. R.H.Allen was not a terrific researcher but is all we have on lots of stuff. The section needs rejigging chronologically but I wish we could find better sources. Hence I found this which talks of Eudoxus of Cnidus going to observe it but not naming it (see p. 88). Cas Liber (talk · contribs) 10:49, 7 September 2020 (UTC)

Irksome Chinese contradiction

First the paragraph says From the imperial capital Chang'an, the star made a low transit across the southern sky, indicating true south to observers, and was often obscured by clouds. Then just one sentence later, it says ...it cannot be seen from the Chinese capital of Chang'an. Which is it?! According to the lat/long listed for the current incarnation of the city, it's at 34°15′54″N 108°57′14″E. Earlier in the article, and discussed here in Talk above, it's stated in theory the northern limit of visibility is latitude 37° 18′N with some variations due to altitude. Does anybody know a Chinese astronomer who can clarify this, please?

Corgi (talk) 23:30, 17 December 2022 (UTC)

Properties and evolution

This paper refers to Canopus as the closest supergiant (yellow supergiant) to the Solar System, although it still cites the A9II classification. It gives it a mass of 9.81 M_☉, consistent with that of a super-AGB star (as Lithopsian suggested above) and the progenitors of electron-capture supernovae (the accepted supernova lower limit is around 8.5 M_☉, although this is not well defined). I've heard Kaler (who suggested a white dwarf fate for Canopus) isn't that reliable compared to other sources. Also, how come Canopus is just a bright giant (II) at 10,700 L_☉ when Iota Carinae has a spectral class of A9Ib and 4,900 L_☉? Stanley Joseph "Stan" (talk) 00:58, 28 March 2024 (UTC)

Luminosity & proximity error

"Since it is more luminous than any star closer to Earth, Canopus has been the brightest star in the night sky during three epochs over the past four million years." Dude, the function of apparent magnitude is due to luminosity and distance. "Since it is more luminous...[it] has been the brightest star" is in error. Zeta Puppis, for example is brighter than any star closer to Earth, but it has never been close to the brightest in our night sky. 172.88.54.93 (talk) 23:03, 25 November 2024 (UTC)