Talk:Sun/Archive_2 References

This page is an archive of past discussions. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page.

Red Giant

On this page it says the sun will be a red giant in 5 billion years, but on the red giant page, it says 6 billion. Does anyone know so we can have consistand info? Jaderaid 12:36, 20 March 2006 (UTC)

Well, you should just get used to these kinds of deviations in astronomy. One of my astronomy-professors once said that to astronomers pi is approximately 1, and he was only half-joking I think. The point is that the numbers used for these types of calculations have so big uncertainties that that different scientists get very different answers. 1 billion years isn't necessary that big a difference in astronomy. :p -- Siljebj, 03.02, 16 June 2006 (UT)

Fate of the Sun

I don't see anywhere in the article about how long the sun will last and its eventual fate. From some sources, I heard it's 5 billions years. Please include this information. Thank you. -- 141.213.196.250 03:42, 3 April 2006 (UTC)

See the 4th paragraph of "General information" in the article. Dragons flight 03:44, 3 April 2006 (UTC)

Somebody keeps snipping that out. There used to be a "future of the sun" section.

hotter than hell

this is amazing how hot can be one star.still over years looks impossible. —The preceding unsigned comment was added by Pentagonshark666 ( talk • contribs) 19:18, April 6, 2006 (UTC) how hot is the sun in degrees?

The Sun's surface is about 9,900°F and its core is about 10 to 22.5 million°F. Football (sport) 10:02, 19 May 2006 (UTC)

The surface of the sun has got an average temperature of 6000 degrees Celsius, while the core's temperature lies around 15 million degreess Celsius. 10.20, 4 August,2006, Lady Stardust

How was the core temperature of the sun measured? Wss it with a very rugged thermocouple and a very long piece of compensating cable? -- Light current 13:47, 5 September 2006 (UTC)

Helioseismology measures the speed of sound everywhere in the Sun. That's only an indirect measurement of temperature, since both the temperature and the local atomic and elemental abundances affect the speed of sound -- but together with existing stellar models, we know the core temperature reasonably well. (Helioseismological measurements of the speed of sound and predicted values from theoretical stellar models tend to agree everywhere to within a small fraction of a percent.) zowie 14:13, 5 September 2006 (UTC)

So its an estimate?-- Light current 14:41, 5 September 2006 (UTC)

It's better than an estimate since the sound speed has been measured directly and the model has been validated via its prediction of structure within the Sun. The core temperature is known to within a few percent. An independent way of verifying the core temperature is by comparing the Kamiokande and Homestake mine neutrino experiments -- Homestake is only sensitive to high energy neutrinos that are produced by a side-chain fusion process and hence is extremely sensitive to temperature; while Kamiokande is sensitive to the main fusion rate. The ratio of the two is a good indicator of temperature. Now that the solar neutrino problem is solved, that ratio is a pretty solid verification of the core temperature measured by helioseismology.

It's always this way with difficult-to-measure quantities -- nobody has a direct measure (you can't just lower in a thermocouple), so you have to take the aggregate of several indirect measurements.

Just out of curiousity, has anyone ever measured the ambient temperature of Hell? Arch O. La ^{Grigory
Deepdelver} 17:30, 5 September 2006 (UTC)

In Revelation Hell is described as containing molten brimstone. Brimstone (elemental Sulfur) melts at 115 Centigrade and boils at 445 Centigrade. Thus the ambient temperature must be in this range. zowie 18:52, 5 September 2006 (UTC)

Then I guess the Sun really is hotter than Hell ;) Arch O. La ^{Grigory
Deepdelver} 05:02, 6 September 2006 (UTC)

Age of the sun

Our article states that it is 4.6 billion years old. Other sources such as [1] and this [2]. What is the basis of our claim? Capitalistroadster 07:06, 7 April 2006 (UTC)

Amelin et al. ("Lead Isotopic Ages of Chondrules and Calcium-Aluminum-Rich Inclusions", Science 297, Sept. 6, 2002.) requires that the time of solar ignition be near but not younger than 4.56717 +/- 0.0007 Gyr ago. Dragons flight 03:43, 9 April 2006 (UTC)

Uh huh.... shouldn't there be a citation in the actual that directly relates to the age of the sun and not just a source with some secondary relation in the discussion page? 209.169.111.193 23:55, 16 October 2006 (UTC)

brightest?

Is it true that our Sun is the brightest star to be seen from one light year away? In other words, it's much much much brighter than all other stars in the greater neighbourhood? -- Sonjaaa 06:05, 20 April 2006 (UTC)

Depends on which direction. One light year in the direction of Sirius, I *think* the Sun would still be brightest, but there aren't any other stars within one light year of the Sun, so it's not much of a neighborhood. If you define "neighborhood" with a radius more like 10 light years, then no, the Sun is definitely not the brightest. You know all about apparent magnitude and absolute magnitude, right? -- arkuat (talk) 06:09, 20 April 2006 (UTC)

This is rather belated, but just for anyone else who might stumble upon this, here goes: If you define a 'local' area to be out to a distance of about 10 parsecs in every direction, then you end up with a group of around 250 stars (about half of these 'stars' are actually binaries. In this set of stars, there are no stars at all of spectral type O or B. The majority are of type M or K. In fact, in this local region, the sun is roughly among the top 10 or 20 in terms of absolute magnitude. Thus it is among the brightest, although it is certainly not the brightest. To answer the original question: At a distance of one light year, the next nearest star (after the sun) would be at least 3 light years away, probably more like 4 or 5. Since there are no tremendously bright stars in our immediate solar neighborhood, I am quite certain that at this distance the sun would still be by far the brightest object in the sky. Grokmoo 18:32, 20 September 2006 (UTC)

age

Since the Sun is about 4 billion years old and the Earth is 4.6 billion years old how has the Earth been around?

according to our articles on each one, the Sun is 4.6 billion years old, and the Earth is 4.57 billion years old. hope that helps.-- Alhutch 03:34, 9 May 2006 (UTC)

Support of life

I'm not sure if this was already mentioned but the sun indirectly supports all known life on the planet yet the introductory paragraph states almost. Can this be changed?

Actually some life, such as that found around black smokers on ocean floors, does not rely on the Sun, so 'almost' is correct. Worldtraveller 00:32, 10 May 2006 (UTC)

There wouldn't be an ocean let alone an ocean floor without the sun, so almost is incorrect. I'm changing it. Eno-Etile 00:00, 17 October 2006 (UTC)

Almost is incorrect, stop changing it at least without some debate. I made the edit because I see no logical argument against my comment, but I wouldn't mind someone restructuring the sentence as it does read akwardly, and I cannot think of a better way to phrase it. Eno-Etile 03:22, 1 November 2006 (UTC)

Ok somone changed it yet again and told me not to remove the almost without gaining consensus but no one is answering me I see no way to get a consensus so until I get debate I WILL continue to change it. Eno-Etile 17:32, 1 November 2006 (UTC)

Sorry, haven't paid much attention here. The 'almost' is because of the presence of black smokers and other sites where subterranean life is driven by geothermal energy rather than solar energy. While it is true that the oceans themselves would eventually freeze if the Sun were not present, the life that is present in black smoker colonies is not being powered by the thermal energy in the oceans -- the oceans are a heat sink for those systems, which are much hotter than the surrounding water. If the Earth were hurled away from the Sun (as in Fritz Leiber's "A Pail of Air" short story) the black smoker colonies would continue to survive for a long time -- even as all surface life perished and the air snowed out onto the surface of the planet. So, it seems to me that the "almost" should stay. zowie 17:39, 1 November 2006 (UTC)

Okay. I made the changes because no one offered an argument against them, yours was a pretty good one. So I gues almost stays. Eno-Etile 17:51, 1 November 2006 (UTC)

glad to be of service. :-) zowie 18:09, 1 November 2006 (UTC)

Aurora(e)

"... causing aurorae, known as aurorae borealis in the northern hemisphere and aurorae australis in the southern hemisphere."

It's probably not a matter of great importance, but the plural of "aurora borealis" should be "aurorae boreales". Likewise for the southern variant ("australes"). However, it may seem pedantic to make the change, since the plural form is probably much less familiar than the singular. Also, I am not completely certain whether the adjective does not refer to another word instead of "aurora" (for instance "pole" or "hemisphere"), so I may be wrong anyway. -- Iblardi 16:28, 4 June 2006 (UTC)

On the one hand, we should use the correct plural; on the other hand, however, it could also be argued that using the correct plural here would mean we should also put Latin words in the right form (nominativus, genitivus, dativus, accusativus, ablativus), so it would be an endless discussion. Having said that, I support the change you named. 82.176.194.151 13:57, 24 August 2006 (UTC)

My point is that IF you choose to pluralize "aurora" to "aurorae", you should also change "borealis" correspondingly. "Aurora borealises" wouldn't offend me, although it would strike me as a bit weird ;)

Iblardi 18:25, 29 October 2006 (UTC)

Opening paragraph

There's a woefully ungrammatical sentence in the very first paragraph. I don't know enough about the topic to infer what was actually meant, but could someone more informed fix it up? Soo 17:23, 12 July 2006 (UTC)

Tell us which sentence? Worldtraveller 17:39, 12 July 2006 (UTC)

Sorry, I hacked it this morning to fix it. The photosynthesis sentence. zowie 19:19, 12 July 2006 (UTC)

Much better, thanks :) Soo 10:56, 13 July 2006 (UTC)

Gas and plasma

The section on the Sun's magnetic field mentions that "All matter in the Sun is in the form of gas and plasma due to its high temperatures." I though that the material in the Sun was 100% ionized, so the amount of gas is trivial? -- Iantresman 19:50, 12 July 2006 (UTC)

In the inner layers, yes, but in the photosphere there's gas and even water vapour. Worldtraveller 20:09, 12 July 2006 (UTC)

But as a whole, the Sun is perhaps, what, 99.999% plasma? To suggest that gases and water vapour are a component would be like suggesting the seas are made of water, gold and drift wood? -- Iantresman 21:50, 12 July 2006 (UTC)

Not really. The water vapour has significant effects on solar properties such as the temperature of sunspots and the like. Worldtraveller 21:59, 12 July 2006 (UTC)

So the perecentage of plasma making up the Sun is about what? -- Iantresman 22:23, 12 July 2006 (UTC)

Slightly less than 100%. From what I've seen of your edits you're extremely keen on emphasising how much plasma there is everywhere, and you seem to be trying to deny there's anything other than plasma in the Sun. Why is that? Worldtraveller 23:03, 12 July 2006 (UTC)

The Sun is composed essentially entirely of plasma, in the sense that the DeBye radius is short compared to the mean free path throughout the Sun. There are some neutrals, especially near the temperature minimum region, but there are enough ionized atoms everywhere that the material qualifies as plasma. Within the solar physics community it is common to refer to "gas" when one is emphasizing the kinetic aspects of the material and to "plasma" when one is referring to interactions between the material and the magnetic field, as in "Active region loops are formed by the force-free magnetic field, but only some of the field lines happen to be full of gas" (loosely quoted from a conversation at the AAS/SPD meeting two weeks ago in Durham, New Hampshire). Another similar quote: "In the corona, beta is low and the magnetic field shapes everything, but in the photosphere, beta is high and the gas runs the show".

These usages highlight the duality of useful approximations in the plasma picture: when one is considering gross morphology, beta is generally either quite high or quite low. In the former case, one can treat the electromagnetic effects as a small perturbation on gas theory; in the latter case, one can treat bulk material as a small perturbation on nearly-massless, nearly-ideal MHD. Only relatively rarely is beta near 1. In those cases, all Hell breaks loose and one cannot use either convenient approximation. That happens in the solar transition region, which is one of the reasons it is not well studied. (Another reason is that the transition region is invisible from the surface of Earth, because it can be seen mainly in extreme ultraviolet).

This is sort of a non-issue of terminology: Alfvén, Chapman, and Parker won -- nobody seriously disputes the importance of plasma physics anymore, or has for four decades or so (although the Electric Universe concept and plasma cosmology crowds go too far in the opposite direction).

Another reason to use the sloppier language is that plasma is a word that is not familiar to the layperson (medical personnel tend to think you're talking about blood products in the sky), so speaking of plasma as a magnetized or electrically conductive gas is a convenient way to get one's point across without confusing the audience. Although something like 99.9% of the material in the Universe is in the plasma state, much less than 0.1% of the material within 50 miles of a human being is in the plasma state, so most humans are not as familiar with it as with the other three states of matter.

zowie 23:52, 12 July 2006 (UTC)

Certainly people tend to use "ionized gas" as a convenient synonym for plasma, and it is trivial to write, for example, "the Sun consists of plasma (an ionized gas)".
While there is a duality in the properties of a plasma, I would argue that its plasma properties far outweight those of its gaseous properties, even though the latter may be in common usage. For example:

Property	Plasma	Gas
State	99.99%	Trace
Fusion	Yes	No
EM emmission	Yes	No
Magnetic field	Yes	No
Magnetic reconnection	Yes	No
MHD	Yes	No
X-rays	Yes	No
Electric currents	Yes	No
Convection	Yes	Yes

It does seems that there are so many properties due to plasma, that are not applicable to a gaseous approximation, that it does seem we are not giving the reader as accurate a picture as we could. -- Iantresman 00:18, 13 July 2006 (UTC)

Some corrections:

Nuclear fusion is not a consequence of the plasma state.
Gases can both emit and absorb electromagnetic radiation.
The magnetic field can permeate gases (though the gas dynamics are decoupled from the field).
The magnetic field can reconnect quite well in gases.
Gases can produce X-rays (e.g. from bombardment by high-energy particles).

As seems to happen frequently between us, Ian, I'm not quite sure what you're driving at. If you want the wording "...plasma (an ionized gas)" rather than "...gas and plasma", I don't see that as a problem. zowie 15:13, 13 July 2006 (UTC)

Thanks for the corrections. I thought that the stellar fusion reactions involved protons and helium nuclei, rather than hydrogen or helium molecules, which would suggest hydrogen and helium plasma?

I'd like to see plasma mentioned in the introductory section, on the grounds that it provides such an influential insight. -- Iantresman 19:11, 13 July 2006 (UTC)

In the core of the sun it is so hot and such an high pressure, that it occours plasma. And what plasma really is, is free electrons and hydrogen (or helium)ions. Because of the heat and pressure has the hydrogen (or helium) molecules split up. That happens when the thermic energy conquers the connecting powers of two different electric loaded particles. But teoreticly seen I think one could call it hydrogen and helium plasma, even if it isn't physically right. 11.04, 4 August, 2006, by Lady Stardust

Actually, Ian's original point is right -- strictly speaking, the entire Sun is made of plasma. Recall, plasma is just a gas that is "sufficiently ionized". Suficiently ionized means that there are enough free electrons and ions floating around to equalize the electric potential ( voltage) everywhere, at least in the absence of dynamic effects. There's an easy-to-calculate distance called the Debye length, which is roughly the size of the largest region that can be positively or negatively charged before electrons and ions move around to compensate and cancel out the charge. If the Debye length is longer than the mean separation between particles, then the material is a plasma. zowie 17:17, 4 August 2006 (UTC)

Sun in culture and religion

Please let me know if this has already been addressed, but the sun is central to a great deal of human culture, religion, etc. This article seems exclusively science-based and fails to address the importance that people attribute to the sun for cultural or other reasons. Is this addressed anywhere on Wikipedia? FunnyYetTasty 14:44, 13 July 2006 (UTC)

Many moons ago there was such a section to the article (sometime last year -- more than 500 edits ago and I can't be troubled to hunt for it) but it never really grew much -- just spawned arguments over whether David Brin's Sundiver book counted as culture. I'd like to see such a thing, if someone felt like writing about Sun-worshiping cultures, megaliths, origins of astrology in the seasonal variation of sun location, etc. Ideally it would start as a section here and then, if it grew too much, spawn off as did the structure and history sections... zowie 15:21, 13 July 2006 (UTC)

It's a potentially huge subject, with numerous cultures and ages worshipping the Sun, with numerous names for the Sun-god, etc -- Iantresman 19:13, 13 July 2006 (UTC)

See also earlier Talk:Sun/Archive 01#Missing culture. For the religious aspects there already is the solar deity article (which could use some more prominent linking here however). For the fiction and other culture I think a separate sun in art and literature should be started. Femto 20:28, 13 July 2006 (UTC)

"our" Solar System

Why the second person? Who is "our"? So much for neutrality! savidan^{(talk)
(e@)} 17:22, 17 July 2006 (UTC)

I can't really see what's not neutral about that. Perhaps arrogant, deigning to speak on behalf of all humanity, and maybe not great encyclopaedic style either, but I'm sure it doesn't contravene WP:NPOV! I wouldn't object if it was changed. Worldtraveller 23:44, 18 July 2006 (UTC)

Slash and burn

Why are people cutting vast chunks out of this article [3]? What good does it do to remove that information from this article? I'm sure you could reproduce it elsewhere without removing it from a featured article. 62.249.214.195 14:25, 27 July 2006 (UTC)

More on Human Understanding

Could anyone put more on history of human scientific understanding of the sun? Like history of attempts at measuring its distance from the earth.

Clarification Needed?

I'm not sure if this is the most relevant place to post this (and please feel free to move it if it isn't), but in the section, "Development of Modern Scientific Understanding", the last paragraph states: "Finally, in 1957, a paper titled Synthesis of the Elements in Stars^[28] was published that demonstrated convincingly that most of the elements in the universe had been created by nuclear reactions inside stars like the Sun."

Now I'm certainly no astronomer, but, by mass, doesn't Hydrogen (by far) comprise "most" of the elements in the universe? Further, virtually by definition, Hydrogen isn't created "by nuclear reactions inside stars". As such, should there be some distinction made in the article to show that in this reference "most" doesn't mean by mass but rather (I assume) by % of elements on the periodic table? 216.240.7.149 00:58, 29 October 2006 (UTC)

Well spotted - it should read "most of the elements heavier than hydrogen". I will go change it now. Sophia 11:40, 29 October 2006 (UTC)
Mass of the Sun
The accuracy with which we know the mass of the sun is limited by the accuracy with which we know the gravitational constant - we know GM_sun to about eight decimal places from observing the planets. Perhaps this is worth mentioning, and giving this number? (Or the mass of the sun in geometrized units) -- Andrew 20:31, 30 July 2006 (UTC)
Rather silly image
Anyone mind if I remove the image with this caption: "Artist's conception of the remains of artificial structures on the Earth after the Sun enters its red giant phase and swells to roughly 100 times its current size."? Tony 07:38, 3 August 2006 (UTC)
I wouldn't miss it. zowie 17:52, 3 August 2006 (UTC)
Kelvin
How many people use Kelvin in every day usage? The temeperature should include Farenheit and Celsius. Dudtz 8/3/06 8:19 PM EST
Just subtract 273 from a kelvin and you get Celsius, it's pretty simple and Kelvin is the norm with planets -- Dulberf 04:44, 4 August 2006 (UTC)
That still does not help people who don't use Kelvin and Celsius. Dudtz 8/5/06 5:32 PM EST
Seriously, I can't imagine a person able to use a computer and browse wikipedia who never heard of the temperature unit Kelvin in school. -- 217.17.197.166 13:06, 25 August 2006 (UTC)
Why not have the temperature in Farenheit? Dudtz 9/12/06 8:05 PM EST
Kelvin is standard in science (where it simplifies certain mathematics). While I've nothing against adding a farenheit value, we do have kelvin wikilinked if people want to look it up. RJFJR 04:14, 13 September 2006 (UTC)
By the way, guys and gals, its kelvins, lower case. Read the article. Urhixidur 03:16, 18 September 2006 (UTC)
Spelling
Worldtraveller- Your personal attacks are really not cool. A British orthographic imperialist made a guideline-violating change here [4]. I corrected it, and fixed a few other things to make the article have a uniform spelling style. That's what the guidelines call for. I'm not pushing U.S. spelling. I'm pushing wikipedia guidelines. Other people are pushing U.K. spellings. But that seems not to bother you. If you want the British Empire to take over the world again, or enjoy attacking people for trying to improve wikipedia articles, please go elsewhere. -- Justice for All 02:16, 14 August 2006 (UTC)
"British orthographic imperialist" or "the article was mostly american english go to a pub, leave this alone!" are not personal attacks?
The manual of style says: If an article is predominantly written in one type of English, aim to conform to that type rather than provoking conflict by changing to another. (Sometimes, this can happen quite innocently, so please do not be too quick to make accusations!)

Even if you're correct in your claim (I counted 19 American spellings vs. 5 British before your first edit), it does not give you the right to attack others. Disputes concerning style may sometimes become heated. If you don't want to harm your cause, stay cool.-- JyriL ^talk 10:55, 14 August 2006 (UTC)
I stand by my claim about 67.151.178.146. A quick look at his editing history shows why. He has been warned, but still disregards the manual of style. I, on the other hand, am trying rigorously to follow the wikipedia policy, yet I was called "dishonest." By the way, why haven't you chastised Worldtraveller for making a "personal attack"? -- Justice for All 11:15, 14 August 2006 (UTC)
I'm not trying to guess what he meant by "dishonest", better to ask him Eno-Etile 00:09, 17 October 2006 (UTC).-- JyriL ^talk 11:59, 14 August 2006 (UTC)
You know most english speaking internet users are American so American english would logically be predominant in most articles. And from an American standpoint it is uncomfortable and unfamiliar to use British spellings (they use too many letters and make little sense phonetically to Americans anyway). Eno-Etile 00:09, 17 October 2006 (UTC)
Opening sentence
"The Sun is the star at the center of Earth's solar system, but that's not important right now."
This is a weird way to open the article, don't you think?
Just some infantile vandalism, fixed.-- JyriL ^talk 22:46, 19 August 2006 (UTC)
Mass of Sun
I updated the mass of the sun and the equivalent number of Earths according to Measurement of Newton’s Constant Using a Torsion Balance with Angular Acceleration Feedback (Physical Review Letters; Vol. 85, Num. 14; 2 Oct. 2000) by Jens H. Gundlach and Stephen M. Merkowitz of the Department of Physics, Nuclear Physics Laboratory, University of Washington, Seattle, Washington 98195. They produced the most precise measurement of “Big G” yet with a value of 6.674 215(92) × 10^–11 m³ kg^–1 s^–2. This allowed them to calculate the mass of the sun (1.988 435(27) × 10³⁰ kg) and the mass of the Earth (5.972 245(82) × 10²⁴ kg), and the equivalent number of Earths (332,946). Greg L 01:27, 24 August 2006 (UTC)
Black Hole at Center of Sun?
My physicist uncle suggested there may be a black hole at the center of the sun. Personnally I find this a plausible argument since the definition of black hole is something so massive that light cannot escape it. —The preceding unsigned comment was added by 164.107.166.152 ( talk • contribs) .
The density/gravity at the suns core is not high enough for a black hole -- Nbound 04:56, 2 September 2006 (UTC)
How can you be sure?-- Light current 05:43, 5 September 2006 (UTC)
The fact that you can type that. Sophia 07:48, 5 September 2006 (UTC)
Im afraid you misunderstand. A small black hole ( Micro_black_hole) could exist at the centre of the sun without us knowing about it. Is Schwarzchild radius could be very small indeed only sucking in the suns mass very, very slowly. Indeed there are theories about mini black holes being at the centre of the earth and even all around us!-- Light current 07:57, 5 September 2006 (UTC)
Don't you just love it when these things are smaller than the planck length? What fun you can have when it can never be measured. Sophia 08:23, 5 September 2006 (UTC)

No it could be bigger than that, but how are you going to detect it at the centre of the sun?-- Light current 08:30, 5 September 2006 (UTC)
How long before Hawking radiation destroys such a tiny black hole? Then again, that might be a way to detect it.... Arch O. La ^{Grigory
Deepdelver} 09:20, 5 September 2006 (UTC) 09:20, 5 September 2006 (UTC)
This is where Occam's Razor is best used. Sophia 12:33, 5 September 2006 (UTC)
Indeed. It's a solution in search of a problem. Other than that neutrino thing I mention below (which turned out to have another solution), I'm not sure why anyone would support the hypothesis. No anomoly, no evience, but I guess some ideas never do die out. You are, of course, free to believe whatever you wish. Arch O. La ^{Grigory
Deepdelver} 17:26, 5 September 2006 (UTC)

Re: 164.107.166.152

I dimly remember reading something about this in the mid-1980s. If I remember correctly, it was proposed as a possible solution to the solar neutrino problem. The hypothesis was falsified, however. Arch O. La ^{Grigory
Deepdelver} 03:43, 5 September 2006 (UTC)PS: Here's the only ref I could find: [5]. Arch O. La ^{Grigory
Deepdelver} 03:48, 5 September 2006 (UTC)
Actually, here's another mention: [6] (Look at the last three lines on "nonstandard assumptions: to wit, what's wrong with the Sun?). Arch O. La ^{Grigory
Deepdelver} 08:03, 5 September 2006 (UTC)
How can massless light not escape a black hole? Dudtz 9/12/06 8:11 PM EST
Because space is curved. EXTREMELY curved near a black hole. Arch O. La ^{Grigory
Deepdelver} 04:28, 13 September 2006 (UTC)
Light has zero REST mass, that's not the same as having no mass (it mainly means that photons always travel at exactly the speed of light). RJFJR 13:55, 13 September 2006 (UTC)
More importantly, light follows locally "straight" lines through space. The point of general relativity is that space is itself curved, so that even straight lines end up going in a different direction after a while. In Newtonian mechanics, space is considered to be flat, and bodies under the influence of a gravitational field follow curved paths through that space. Einstein moved the curvature to space itself -- space itself is thought to curve as a result of the presence of mass within it. That explains nicely the duality between gravitational charge and inertial mass, but it also means that even things which have no mass (such as light) must follow curved lines.
For more information you can browse general relativity or follow the links to John Baez's very nice exposition of general relativity. zowie 20:16, 13 September 2006 (UTC)
Spacecraft
Has any man-made object ever made contact with the sun? I know it would never make it there, it would just burn up, but I am curious. -- Cngodles 15:54, 8 September 2006 (UTC)
I believe the answer is No. NASA had plans to launch a Solar probe spacecraft that would have flown through the solar corona, and in 2000 they even collected and reviewed proposals for instruments, but one of the first actions of the Bush administration was to cancel it, 13 days after taking office in January 2001. zowie 20:19, 13 September 2006 (UTC)

Great expense of money lets spend lots of money to send something into space that not only are we never getting back but were also melting in the largest furnace ever, could just light the money on fire and use it to warm some homeless people. Eno-Etile 00:13, 17 October 2006 (UTC)
Solar Probe was designed to survive the close flyby, and a related mission may yet fly eventually. The Solar Probe mission in its entire eight-year development, launch, and flyby phases would have cost about as much as 12 hours of the Iraq occupation. zowie 17:32, 28 October 2006 (UTC)

A 1972 solar impact mission was considered, using a Saturn 1B vehicle with a Jupiter gravitational assist. [7] You might also check whether the objects at the Earth-Sun L1 point were self-contained, as if they used rocket boosters see where the boosters went (such as in a decaying solar orbit): List of objects at Lagrangian points#L1 ( SEWilco 06:22, 28 October 2006 (UTC))
Precision
The infobox was just changed to read ! align="left" | Surface temperature | 5785 K
This implies a precision of measurment to the degree. 5780 would imply +/- 5 degrees or so. I rather doubt we have measurements to the degree. Do we know a tolerance for this? RJFJR 17:42, 12 September 2006 (UTC)
Luminosity?
The article states the solar luminosity is 3.9E28 lm (39,000 Ylm), which translates to about 3,100 Y cd (since the Sun radiates into 4π sr). This source states the solar illumination at Earth's equator at high noon is about 1000 lx. Using a 1 m² surface, we can compute it subtends a solid angle of about 1.787E-22 sr (using 1 AU distance), so the Sun's equivalent point luminosity is 5.6E24 cd (5.6 Ycd). The discrepancy is a factor of 554!
Which is right?
Urhixidur 02:28, 18 September 2006 (UTC)
Your source for the illumination at the earth's equator is clearly wrong. Compare with the values at lux#Explanation. Also, you made a math error. It's 4.4×10^-23 sr. 100 klx at 1 au is 2.2×10²⁷ cd, much closer to your value for the Sun's output. The remaining difference is probably due to absorption and scattering in the atmosphere. The sky is blue for a reason...-- Srleffler 04:37, 18 September 2006 (UTC)
This source states a V-magnitude zero star outside Earth's atmosphere puts out 2.54E-6 lx. The atmosphere transmits 82% in the visual, i.e. it dims 0.2 magnitudes. Since the Sun's V magnitude is -26.8, we're talking a 27.0 magnitude difference, hence the Sun is about 160 klx at ground level. This yields in turn a luminosity of about 900 Ycd. The discrepancy shrinks to a factor of 3.5.
The same source also gives a Mv=0 star outside Earth's atmosphere as = 2.45E29 cd. Since the Sun's Mv = 4.8, (5.0 on the ground), we have Sun = 2,450 Ycd.
Urhixidur 02:42, 18 September 2006 (UTC)
"Puts out" 2.54E-6 lx is not a meaningful expression. Lux is a measure of illuminance. You have to specify where it is measured. I presume the source meant that the outer surface of the Earth's atmosphere is illuminated with that level of illuminance.
I think you made another error. Shouldn't the magnitude difference at the Earth's surface be -26.6? That gives 111 klx, in better agreement with Lux.
It's not clear what the cited value in candelas refers to. Clearly not all stars with an apparent magnitude of zero have the same luminous intensity. Some are much further away than others. The source has either made some specific assumption, or has made an error. I suspect the former, since the source clearly says "Apparent magnitude is thus an irradiance or illuminance". One cannot directly express apparent magnitude in candelas.-- Srleffler 05:02, 18 September 2006 (UTC)
Right on all counts, Srleffler. Back of the envelope calculations sometimes go slightly wrong...The source gives the candela value of an absolute magnitude Mv=0 star, meaning the star is 10 pc away. The specific luminosity distance is not important; what matters here is the Sun's absolute magnitude. It is silly of me to include atmospheric extinction in the calculation above (the Sun's luminous intensity doesn't depend on Earth's atmosphere). Mv=4.8 yields 2950 Ycd.
Urhixidur 15:54, 18 September 2006 (UTC)
Yet another stab at it: the solar surface luminosity is given by this source as 2E9 nits (cd/m²); multiplying by the apparent disc (πr², not a bad approximation since there is little limb darkening), we get 3044 Ycd. Times 82% atmospheric transparency, about 2500 Ycd.
Clearly the very first source is wrong.
Urhixidur 03:02, 18 September 2006 (UTC)
Further update: various Sun luminances are bandied about:
900 Mcd/m² http://www.crompton.com/wa3dsp/light/light4.html

1 Gcd/m² http://www.hardwaresecrets.com/article/208, http://www.naturescapes.net/072006/rh0706_2.htm, http://www.hdrsoft.com/resources/dri.html

1.6 Gcd/m² http://www.du.edu/~jcalvert/optics/lumens.htm

2 Gcd/m² http://www.ece.ucsb.edu/~manj/ece181b/L12(shading).pdf

3 Gcd/m² http://stjarnhimlen.se/comp/radfaq.html
The Sun's photospheric surface area being almost exactly 6×10¹⁸ m², the values above yield luminous intensities ranging between 5500 and 18 000 Ycd. I prefer to trust http://astro.kent.ac.uk/mds/507/ph507lecnote06-week1.doc, inasmuch as it takes into account the V filter's response curve. One can always argue the V filter is less sensitive than the human eye by a factor of between 1.8 and 6 times, in order to reconcile the figure with the luminances quoted above. The V luminance of the Sun is 0.484 Gcd/m², for comparison purposes.
Urhixidur 15:54, 18 September 2006 (UTC)
NB: You can't convert luminance into luminous intensity by multiplying by the Sun's surface area. It has the right dimensions, but isn't the same thing. Per WP:NOR, you should not attempt to derive a value of luminous intensity to include in an article. If you can't find a published value of the quantity you want, you should not include it.-- Srleffler 23:23, 18 September 2006 (UTC)
It is the same thing if you're far enough that you can consider the Sun to be a point source. Not the case within most of the solar system, but true beyond its limits. As for WP:NOR, converting values is not "original research". Or are you saying one can't convert a value from miles to klicks, or gauss to teslas, etc., unless one can find a published source? That'd be silly. Urhixidur 17:36, 28 September 2006 (UTC)
Reading this discussion I can't help but think, "WTF?" The important aspect of the luminosity is the bolometric luminosity, which determines (among other things) how much heat is delivered to the planets and how long the Sun can last. The luminous intensity depends on the psychology and biology of human vision, which has very little relevance to the star itself. My point: why bother with measurements in candelas or lumens at all? Why not stick with Watts or Watts per square meter? zowie 16:07, 18 September 2006 (UTC)
Zowie is quite right; I tend to share his "physicist's snobism" about the utter irrelevance of the human observer. But Wikipedia nevertheless has a responsibility to answer a child's question of « How bright is the Sun? ».
Searching the NASA ADS for a reliable value of the solar luminance or luminous intensity, I found M. Menat (1980), Atmospheric phenomena before and during sunset, Applied Optics, Vol. 19, (Oct. 15, 1980), pp. 3458-3468, which gives in figure 8 the apparent solar luminance during sunset/sunrise. The text states « the maximal average luminance of the Sun is about 1.5×10⁹ cd/m² », which matches the mid-range value quoted earlier of 1.6 Gcd/m². Figure 9 is instructive, showing the zenithal spectral luminance peaking at 550 nm, which happens to be the monochromatic candela definition.
Menat, for the visibility function (equation 45), refers us back to:
L. Levi, Applied Optics (Wiley, New York, 1968), pp. 233 and 514.

M. P. Thekaekara, R. Kruger, and C. H. Duncan, Appl. Opt. 8, 1713 (1969).

G. W. Paltridge and C. M. R. Platt, Radiative Processes in Meteorology and Climatology (Elsevier, New York, 1976), pp. 53 and 55.
Urhixidur 17:12, 18 September 2006 (UTC)
Did you misquote there, or is the paper doing something funny? What is "spectral luminance"? Do they mean spectral radiance? I'm surprised, anyway, I was sure the solar spectrum peaked further to the blue than that. Or is that for sunlight transmitted through the atmosphere? -- Srleffler 23:23, 18 September 2006 (UTC)
Going back to http://astro.kent.ac.uk/mds/507/ph507lecnote06-week1.doc, it turns out the « One star, Mv=0 outside Earth's atmosphere = 2.45×10²⁹ cd » line is wrong by a factor of ten, and should read 2.45×10³⁰ cd. This can be verified by looking a the other values quoted « 1 mv=0 star outside Earth's atmosphere = 2.54E-6 lux » and « 1 mv=0 star per sq degree outside Earth's atmosphere = 0.84E-2 cd/m² » and their conversions (into stilbs and phots). These are all cross-consistent. Plus, using the 2.54 µlx figure and scaling it to the Sun's apparent magnitude of -26.8, we do get 133 klx outside the atmosphere (109 klx inside), which matches the widely quoted maximum sunshine of 100 klx. Turning to luminance, we see the Sun puts out 3.75E+28 lm (which also matches the 100 lm/W value), corresponding to 6.16 Glm/m².
Turning to Menat's figure of 1.5 Gcd/m², it seems too weak by a factor of about 1/2. The Sun is a near-perfect Lambertian radiator, and therefore the illumination predicted by Menat's figure is 1.5 Gcd/m² × 1 Em² (a Lambertian sphere's flux is 2/3 πr² -see [8]) × 44.68 ysr (a square metre at 1 AU) ÷ 1 m² = 68 klx (×82% for the atmosphere = 55.8 klx). There's probably an error on my part here, can anyone spot it?
Urhixidur 19:45, 29 September 2006 (UTC)
If you're looking to answer a child's question, isn't it a bit odd to do so in units that are meaningless to most scientists, let alone anyone else? I do not see much value at all in trying to derive the Sun's brightness in candelas or lumens. Your tortuous workings out do look very much like original research. "physicist's snobism" is an incredibly inaccurate and rather rude thing to accuse someone of, who just wants to keep the article simple and accessible. 85.210.25.62 23:24, 29 September 2006 (UTC)
Order of External Links
Is there any particular order that is generally used for external links? If so, where can we find the guidelines? Rylan42 01:59, 24 September 2006 (UTC)
Safety
I've added some bits on the dangers of observing the Sun. I have laid it on a bit thick, but I think that is appropriate in this case. Man with two legs 10:41, 25 September 2006 (UTC)
When we were kids, we used to play a game to see who could look at the Sun with wide open eyes, without blinking, for the longest time. This was often for minutes on end and played frequently. Our parents didn't know about this and at that age we certainly weren't going to tell them. The upshot of this is that I am in the final years of my life, have vision good enough to read fine print without glasses, and have never had cataract surgery or any other eye problems. I'm not suggesting that our childish games improved our vision, but on the other hand, it certainly does not seem to have done any harm. Of course, a different genome or physiology would give different results, but the dangers of direct looking at the Sun do seem to be exaggerated. Paul venter 08:49, 26 October 2006 (UTC)
...during the Archean period, the Sun was only about 75% as bright as it is today. I think it explains itself. —The preceding unsigned comment was added by 88.9.181.35 ( talk) 22:52, 9 December 2006 (UTC).
The snag is that by the time you find out if you got away with it, it is too late. Many other people have been damaged by looking at the sun. It is especially dangerous when any kind of telescope is used. Man with two legs 12:56, 31 October 2006 (UTC)
Mama always told me not to look into the eyes of the sun
But Mama, that's where the fun is ... Daniel Case 03:37, 28 October 2006 (UTC)
The Sun disambig
For anyone watching here, I just redirected "The Sun" (i.e., with the definite article) to this page but expect to get reverted again. I'm surprised every day on the Wiki, but this was absolutely astounding. Any comments on that redirect talk page welcome. Marskell 23:22, 28 September 2006 (UTC)
Artist's (mis)conception of the red giant phase
I got rid of the "artist's conception" image because (A) it doesn't really focus on the Sun, (B) it is misleading. There is no reason to suppose that artificial structures will survive the intense heating from the red giant phase of the Sun's "life". Without some back-of-the-envelope justification, at least, for the presence of cracked mud and non-burned telegraph poles, the picture is misleading and worse than useless in this context. (Don't get me wrong, I think it's kind of cool -- just not appropriate here). Please discuss here before adding it back in. zowie 07:08, 14 October 2006 (UTC)
Should we talk about how the sun is going to explode and engulf the Earth
??? Zabrak 02:38, 28 October 2006 (UTC)
Only if that was going to happen. Read Sun#Life_cycle. ( SEWilco 02:50, 28 October 2006 (UTC))
"Average" sized?
Copied from User talk:Howcheng:
The Sun isn't an average-sized star. It's above-average sized. Average-sized stars are classed as red dwarfs. Please can you fix this? -- Jrothwell ^(
talk) 17:17, 28 October 2006 (UTC)
Solar evolution
The Dutch Wikipedia-page includes a table on solar evolution. I don't know how reliable it is scientifically, but it has some sources listed: http://nl.wikipedia.org/wiki/Zon Iblardi 19:24, 29 October 2006 (UTC)