Talk:Effective temperature

Planets

In the article, at no point is the variable "A" being used in the equations defined as the albedo, it is just assumed. I think we should add that in, to avoid confusion of where this "A" variable comes from. brithans 23:10, 2008/11/20, (UTC)

The definition given here does not seem to match the one used in the literature by Lopez-Morales & Seager (2007). I am an astronomer but I work on stars, not planets. Anyone able to comment on this? I do know for sure that Sara Seager is an expert in the field. Timb66 22:02, 10 August 2007 (UTC)

There are two differences between the formulas, an inessential one where L&S use $T_{*}$ as a proxy for luminosity (equivalent by the formula in luminosity for L when f is set to 1/4) and a more creative one where they incorporate a so-called "reradiation factor" f. In the L&S article the value of 1/4 for f corresponds to the explicitly stated assumption of this article that the planet radiates uniformly from its entire surface, day and night. L&S consider f ranging from 1/4 to 2/3, the latter being the other extreme where the planet reradiates all the absorbed energy during the day (in fact immediately when f is exactly 2/3). This would happen for example with an atmosphere or topsoil that is not a strong reflector (when A = 1, f becomes irrelevant) yet is such a good insulator that the planet radiates nothing at all at night. Such a blanket would raise the effective temperature of the planet by a factor of (8/3)^1/4 = 1.278 over what it would attain if allowed to radiate in all directions. Some of Seager's planets orbit their parent star so closely as to make them as hot as a brown dwarf star. High temperatures presumably accelerate reradiation, making f >> 1/4 likely.

There is nothing standard about this "reradiation factor," which even Seager doesn't use consistently from one paper to the next. In Rowe, Matthews, Seager et al the same formula as in L&S appears but with f scaled by a factor of 4 so as to range from 1 to 8/3, except that there it is only allowed to range from 1 to 2 (RMS seem not to have computed the immediate-reradiation factor correctly). Until this new formula settles down and gets some traction the present article should stick to f = 1/4. Even if f gets as high as 1/3 (anyone know if it gets that high for any solar planets?), as a correction factor this would only add 7%, not much given that "effective temperature" is only a conceptual notion and not something one can actually measure, and that the actual variations due to other effects can be much greater.

However I do like the approach of using their $T_{*}$ formula, in the form

$T=T_{*}{\sqrt {\frac {R{\sqrt {1-A}}}{2D}}}$

which is what the article's formula

$T=\left({\frac {L(1-A)}{16\pi \sigma D^{2}}}\right)^{\tfrac {1}{4}}$

reduces to when L is replaced by the formula for L in the luminosity article. A big advantage is that it replaces two relatively obscure quantities, L and σ, by the familiar quantity $T_{*}$, 5780 K in the case of the Sun. Here (R/2D)² is simply the fraction of the sky (the whole sphere, not just the day half) occupied by the Sun, assuming distance D >> solar radius R. It's a more natural and appealing form for the formula for effective temperature of a planet in terms of that of its parent star. And f is easily incorporated when appropriate simply by replacing 1−A by f(1−A), where f is defined so as to range from 1 to 8/3---the 1/4 to 2/3 version seems like a bad idea. --Vaughan Pratt (talk) 06:40, 23 July 2008 (UTC)

The definition of Effective temperature in connection with a planet, or any other body heated by an external source, requires a physical impossibility, an object with an albedo that also emits as a blackbody. The albedo arises because the material of the planet interacts with the incoming radiation to reflect part of it, if we forget transmission (conduction is excluded by the vacuum of space) the rest of the radiation interacts in the classical manner with charges in the material when it is converted into heat by absorption. The absorbing charges also radiate heat on their own account and, to achieve thermal equilibrium, the out going heat equals the incoming heat, the absorptivity and the emissivity are equal as required by Kirchhoff's law of thermal radiation. I suggest the article be revised to incorporate this important matter--Damorbel (talk) 17:07, 16 October 2008 (UTC)

I believe what you're saying is that it's impossible for the actual temperature of a planet in equilibrium to be equal to the effective temperature, unless it's a blackbody. I think you're right there. However, that impossibility doesn't really complicate the definition of effective temperature, which is a quite simple thing, and applies to luminous and nonequilibrium and nonblackbody and all sort of things. It's just a definition that converts radiated power per area to a temperature. It does not try to say that anything is actually at that temperature. Anyway, it's not clear what in the article you are saying needs to be revised. By the way, the fact that emissivitiy equals absorptivity is often over-interpreted to mean that there's a factor similar to albedo that affects radiation; this is typically not the case, since albedo is dominated by wavelengths of sunlight, and radiation by much longer IR wavelengths, where the factors can be very different. That's why there are things like greenhouses; glass readily passes visible, but reflects most of the long-wave IR. Similarly with greenhouse gases. Dicklyon (talk) 04:24, 17 October 2008 (UTC)

As you say the definition of effective temperature "does not try to say that anything is actually at that temperature" why not include an explanation to the actual temperature without the confusing introduction of the albedo? Since the albedo of a planet is known the link is very simple. For stars the matter is more problematic because the albedo is more difficult to determine, but it doesn't mean it is absent. --Damorbel (talk) 09:02, 19 December 2008 (UTC)

The albedo of a planet is the fraction of incident light reflected, which is pretty much unrelated to the emissity, since the relevant wavelengths are so different that the weighted-average absorptivity (which equals emissivity) is very different when weighted over the different wavelength ranges of absorption versus emission. That's why the concept was introduced; it gives an idea what blackbody temp would emit the amount of radiation in question, without having to know the emissivity in that long-wavelength range; it provides a useful approximation and bound on the actual temperature, and is easy to convert if you do know the relevant emissivity. Dicklyon (talk) 16:41, 19 December 2008 (UTC)

Your assertion that emissivity is unrelated to albedo is contrary to both Kirchhoff's law of thermal radiation and equally the Fresnel equations. To explain, electromagnetic radiation is absorbed (and emmitted) by accelerating electric charge. For both absorption and emission it is the same electric charge that is accelerated, absorbed radiation increases the energy of a vibrating molecule, and the charge will radiate according to its own mechanical resonances, the wavelength of the absorbed and emitted radiation are not relevant.

I'm well aware that absorptivity equals emissivity, at each individual wavelength. But read my explanation again, instead of ignoring it. Dicklyon (talk) 18:19, 20 December 2008 (UTC)

The Fresnel equations explain why materials that reflect light are less than perfect emitters, light arriving at the interface between two materials with differing refractive index is partially reflected as the Fresnel equations explain, but this is equally valid if the electromagnetic radiation source is in the low or the high index material. If the source is in the high index material the radiation incident beyond the critical anglegives rise to total internal reflection and cannot escape, thus a body, black or coloured, emitting radiation will have an emissivity less than 1, i.e. it cannot emit with the same intensity as a black body. This is a fundamental matter for all instances of the transmission of electromagnetic radiation, notably it impacts light emitting diodes whose efficiency is limited by the phenomenon LED. This is another reason (other than thermodynamic considerations and Kirchhoff's law of thermal radiation) why albedo has no effect on the equlibrium temperature of a planet. --Damorbel (talk) 17:59, 20 December 2008 (UTC)

I don't think you'll find a planetary scientist who will agree that albedo has no effect on planetary temperature. Your simple-minded analysis is not a good model. Dicklyon (talk) 18:21, 20 December 2008 (UTC)

Simple minded? Where? Is it just "all wrong" or are you able to clarify which bit? I mean nobody has cast doubt on the Fresnel equations, the problems with the output of LEDs limits their performance in a very real way and Kirchhoff's law of thermal radiation is based on the second law of thermodynamics

Simple minded in that ignoring the wavelength dependence of absorptivity/emissivity leads you to a false conclusion. Dicklyon (talk) 00:34, 21 December 2008 (UTC)

You are quite wrong about planetary scientists, the assumption that the earth radiates "as a black body" is a relatively recent innovation, Callendar did not mention it in 1938, neither did Dobson in 1946 Manabein 1961 or 1975

Nobody assumes the earth radiates as a black body, and I have not implied that they do; all recognize that there's a greenhouse effect that raises the actual temperature to well above the effective temperature. Dicklyon (talk) 00:34, 21 December 2008 (UTC)

The earliest reference I have found is Hansen in 1981 and he gives no reference, only giving it the name "Greenhouse Effect". I have looked very hard but I have not found an earlier. Hansen does not use the words "black body" but his equations (1) & (2) may be thought to be explicit on this. If you have an earlier example I should be very pleased to have sight of it. --Damorbel (talk) 21:47, 20 December 2008 (UTC)

Greenhouse effect is a popular name for the effect that makes greenhouses work: namely, making a covering that's relatively transparent to visible sunlight, but relatively reflective in long-wave IR, so that the temperature inside greatly exceeds the effective temperature. Here are about a thousand earlier uses of the term. And Space Physics and Space Astronomy, by Michael D. Papagiannis is a particularly good analysis of the planetary temperature problem, including greenhouse effect, from 1972. This 1976 book explicitly couples the greenhouse effect and the black-body calculation. Both of these suggest that the greenhouse effect isn't really what keeps greenhouses warm. And here is a planetary "effective temperature" calculation from 1904 (but no greenhouse effect, as it claims the atmosphere is transparent to the longer waves, which we now know is backwards). Dicklyon (talk) 00:34, 21 December 2008 (UTC)

Thanks for the references. You assert that "Nobody assumes the earth radiates as a black body" But the book you reference by Papagianis explicitly says "Earth radiates as a black body" on p10. But again there is no serious analysis of this, all he says is "Let the sphere radiate like a black body at an ..." this is not exactly solid reasoning. The formula he has for the equilibrium temperature contains the term (1-S), S being the albedo, the reflected part. The albedo represents the energy not absorbed. The same reasoning also applies to emitted radiation, the dielectric characteristics that apply to absorption (i.e, partial reflection) apply symetically to the reverse process of emission. The spectral characteristics are also symetrical, thus by Kirchhoff's law of thermal radiation, independent of wavelength. Spectral characteristics can arise from mechanical resonance as in gases or reflection as in thin films,equally symetrical for absorton and emission.

Another confusion arises by assuming that something with the spectral characteristic of a black body has the same radiative efficiency as a theoretical black body. If your theoretical black body was radiating let us say from under the sea, a fair percentage of its radiation is trapped by total internal reflection according to the Fresnel equations. Thus the sea, comprising 70% of the Earth's surface, cannot radiate with the efficiency of a black body.

Infrared images of planet Earth show that much of the heat energy leaving the Earth leaves from H2O and CO2 with a spectrum the inverse of the transmission spectrum, this is not remotely "black", without even considering the emission temperature.

You claim to be "well aware that absorptivity equals emissivity" and I must "read my explanation again", but the article itself makes the unjustified black body claim. --Damorbel (talk) 17:24, 22 December 2008 (UTC)

I don't get to see page 10 in that book. Can you quote the full sentence you're referring to? Also, please quote the sentence in the article that you feel is an unjustified claim. I'm not able to discern what's got you confused. Dicklyon (talk) 23:17, 22 December 2008 (UTC)

HaHa! Who is confused? Standard science, still valid after nearly 200 yr. makes it clear that thermal radiation cannot escape 100% from a body (black or otherwise) with a refractive index >1.0, yet this article, in the paragraph headed "Planet"says (l.1) "can be calculated by equating the power received by the planet with the power emitted by a blackbody of temperature T." and again on l.6 "The next assumption we can make is that the entire planet is at the same temperature T, and that the planet radiates as a blackbody." In the book you reference page 10 paragraph 1.3 line 4 it says "Let the sphere radiate like a black body at an effective temperature T_e ."

If you look at the subject of the sentence that you omitted from your quote, it is "The effective temperature", and is correct by definition of effective temperature. If it had said "The temperature," you would have a valid complaint. Can you see the logic of basic things on definitions? The "assumption" and "let" are formal devices to apply the analogy suggested in the definition of effective temperature, an analogy to a black body that emits the same total power. Dicklyon (talk) 20:00, 23 December 2008 (UTC)

I suggest you check Kirchhoff's original work, there is a translation available here [1]. The pdf file is the best, see p73, the section entitled "On the Relation Between the Emissive and Absorptive Powers of Bodies for Heat and Light". His basic law for the hypothetical black body is described on p78; on p89 he extends this to non black (arbitrary) bodies. He could be wrong of course and the "Earth radiates as a black body" scientists could be right, but just saying so is not really enough, even worse is - "The next assumption we can make..."--Damorbel (talk) 07:43, 23 December 2008 (UTC)

As I've said, I'm familiar with it, and nobody doubts it. There are no "Earth radiates as a black body" scientists, and if there were they'd be wrong. But why you want to keep setting up such a flimsy straw man is puzzling. Dicklyon (talk) 20:00, 23 December 2008 (UTC)

So is the "assumption that Earth radiates as a black body" is false? This is the assumption behind the (false) claim that the Earth's equilibrium temperature is 255K (without the Greenhouse effect). A black body is a far more efficient radiator than one with an albedo of 0.31, it would (if it existed) will be a lot cooler when reradiating the power coming from the Sun. Using Kirchhoff's law of thermal radiation you will discover that the albedo plays no part in determining the temperature of any planet, so the formulas for the effective temperature of a planet given in this article are quite incorrect. It seems to me that the idea of the Earth "radiating like a black body" is taught in many courses and you will never get a pass for disagreeing with your teacher. However as Einstien noted "The only thing that interferes with my learning is my education". It is time to learn about the planets and time to throw away the weird ideas put into "education" by professors who don't check what they are teaching. --Damorbel (talk) 21:36, 23 December 2008 (UTC)

Calling an assumption "true" or "false" misses the point, but yes, the assumption that the earth radiaes as a blackbody is not true, just a hypothetical. There is not claim that the Earth's equilibrium temperature is 255 K, but if there were, then yes, that would be false, too. Now, adding "without the Greenhouse effect" it gets more dicy, since it depends on what one means by that; if it means "without consider that the emissivity is less than unity", then yes, that would be OK. But where are you finding this "without the Greenhouse effect" thing? I can't tell you whether the passage is correct without seeing the context. It seems to me that what interferes with your learning is your inability or unwillingness to look beyond your simple albedo model and follow a logical argument that is still consistent with Kirchoff. Your conclusion that "albedo plays no part in determining the temperature of any planet" would only be true if emissivity was a constant function of wavelength, but it's not; no planetary scientist will agree with you on this; you might consider listening to why. Dicklyon (talk) 22:05, 23 December 2008 (UTC)

The assunmption that the Earth radiates "as a black body" is the source of the IPCC's assertion that the Earth has an effective emission temperature of -19°C (254K). Now the IPCC may be mistaken when it imagines that this effective emission temperature would be realised in the absence of greenhouse gases but they make it very clear in the TAR that it is the "greenhouse gases" that stops the Earth having this low average temperature. The IPCC calls this "the natural greenhouse effect", it explains that "greenhouse gases" warms the surface 33°C above this so-called "effective temperature". But surely if the effective temperature is the 281K predicted by Kirchhoff's law of thermal radiation then there is little or nothing for the Greenhouse gases to do? --Damorbel (talk) 13:51, 26 December 2008 (UTC)

Obviously they're not actually assuming it radiates as a blackbody if they're talking about greenhouse effect. It's called a supposition. And how do you know what they are imagining, if you can't follow their logic? Is there a link that mentions the 254 imagination you refer to, or did you make that up? I can't find it on that site you linked. And once again, the 281 K predicted by Kirchhoff's law, if that's what it comes out to, is not an effective temperature; it's a modeled actual temperature. I believe the point you're trying to make, obtusely, is that you don't need to invoke "greenhouse effect" if you invoke "Kirchhoff's law with the appropriate parameters; I'm pretty sure that much is correct, but the appropriate parameter is not necessarily equal to the absorption in the visible (one minus albedo), since the relevant wavelength range is different. The greenhouse effect is an attempt to explain where the relevant parameter comes from, which is primarily from atomospheric gasses. Dicklyon (talk) 21:20, 26 December 2008 (UTC)

Would I be correct if I understood the definition of Effective temperature had nothing to do with the actual temperature averaged over a planets surface? --Damorbel (talk) 12:20, 28 December 2008 (UTC)

"Nothing to do with" would be more correct than your other interpretations. Dicklyon (talk) 17:42, 28 December 2008 (UTC)

Don't be shy! What then is the effective temperature of the Earth? Should the effective temperature be used for estimating/calculating the actual temperature of a planet? Do you happen to know what the temperature is of the Earth without Greenhouse gases in the atmosphere? --Damorbel (talk) 18:58, 28 December 2008 (UTC)

I recommend you consult sources to try to find good answers to your questions. I am no expert. Dicklyon (talk) 19:47, 28 December 2008 (UTC)

"I am no expert." Then how is it you are so informed on this matter? Little of this stuff is accessible unless you get to the basics of Electromagnetic radiation interacting with matter. The link to Kirchhoff's law of radiation explains very clearly why wavelength does not affect the radiation balance and the Fresnel equations explain the rest of the none existent "perfect blackbody". Seems to me that this is just another Green Doom scenario that planet Earth is on a CO2 knife edge, balanced between freezing and baking. What a drama that would be! Almost a pity it isn't true --Damorbel (talk) 22:00, 28 December 2008 (UTC)

I like to stay well informed, yes. I'm sufficiently well educated in the underlying physics, but am not an expert on the planetary science questions you asked. I know enough to realize that this topic has nothing to do with Doom, as it long predates the understanding of how humans are adding to the greenhouse effect. As to not depending on wavelength, I'm not sure where in the linked book you are referring to; many pages talk about things being dependent on "wave length"; if you can cite a page (in the PDF) or a quote that explains "why wavelength does not affect the radiation balance" I'll take a look at it; it may be talking about a system in equilibrium, unlike the star/planet system where absorption and emission are happening at very different wavelengths. Dicklyon (talk) 23:29, 28 December 2008 (UTC)

Question about the first and second sentences

The first sentence of the article says "The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation." In the case of a star the motivation for this definition is clear, as is the definition itself. In the case of a planet however the motivation is less clear since planets take as well as give, and the definition is even less clear as a result.

In particular a planet emits two kinds of radiation, insolation reflected by water vapor, snow, etc, at a short wavelength and thermal emission at a much longer wavelength, around 23 times longer in the case of Earth. Reading between the lines of the formula for planets one deduces that reflected insolation is not counted as part of the planet's emission. This still leaves unanswered various questions, e.g. the status of insolation trapped in the atmosphere during the day and radiated away at night before it has reached the surface.

Does there exist an unproblematic interpretation of the first sentence of the article in the case of planets? --Vaughan Pratt (talk) 07:14, 8 November 2009 (UTC)

The reflected part is counted in the Albedo; I would assume that radiation absorbed in the atmosphere and later reradiated is treated the same as radiation absorbed anywhere else and reradiated later -- some planets are nothing but atmosphere after all. Dicklyon (talk) 17:03, 8 November 2009 (UTC)

I 'undid' this edit [[2]] . Statements asserting that the temperature of a body is somehow dependent on the ammount of energy it reflects are completely contrary to all experimental observations in thermal physics, however many claims are made for formulas that are (supposed) to show that it is. --Damorbel (talk) 07:03, 13 December 2011 (UTC)

Regarding the second sentence "When the star's or planet's net emissivity in the relevant wavelength band is less than unity (less than that of a black body), the actual temperature of the body will be higher than the effective temperature. The net emissivity may be low due to surface or atmospheric properties, including greenhouse effect." I suggest that the effective (black body) temperature is not altered because the emissivity remains at 1.000 for the whole planet+atmosphere system. What then is implied by the words "actual temperature" because the implication seems to relate to surface temperature? The surface temperature of a planet with radiating gases in a significant atmosphere has little to do with the direct solar radiation that surface currently receives, as is obvious on Venus. No radiation calculations explain the temperature at the base of the nominal troposphere of Uranus where it is 320K despite there being no direct solar radiation or any surface.

User http://en.wikipedia.org/wiki/Special:Contributions/192.54.176.191

Any body know who this guy is ? 192.54.176.191 Currently making controversial statements and changes without discussion - has no talk page either. --Damorbel (talk) 15:22, 13 December 2011 (UTC)

He writes (In his explanation for his reversal) " AGAIN removed unnecessary disclaimer. BEFORE reenter please read at least one article about this subject. http://arxiv.org/abs/astro-ph/0503457 In any case these formulae are explained in any astronomy 101 course"

Which is simple abuse. In addition he wants "any astronomy 101 course" to be accepted as 'reliable'. This is a matter of physics and to be more precise - electromagnetic radiation. Is an astronomical student a reliable source for physics, particularly one who doesn't explain his reasoning?

The 192.54.176.191 link cites the (1 - A) factor (as does the article) that requires a planet to emit as if it was a perfect black body while at the same time reflecting the fraction A. Such a position is quite ipossible to sustain of course, even Fourier knew this, and the link makes no effort to justify it. The assumption is frequently made by astronomers and climatologists but it never gets beyond that. Wikipedia should not be passing 'assumptions' off as reliable science. --Damorbel (talk) 16:12, 13 December 2011 (UTC)

I checked the talk page and found no support for that Sept. 2010 tag on this talk page. If you want to tag it, please make a discussion section to say what you think the issue is. Dicklyon (talk) 03:45, 14 December 2011 (UTC)

Also please read the lead sentence that says "The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation." This is nothing like assuming any particular way that the planet radiates. Dicklyon (talk) 03:47, 14 December 2011 (UTC)

Dicklyon, I appreciate your contributtion. The problen with 'Effective temperature' is that it doesn't indicate any real temperature. What it does do is give the temperature that would be indicated by a heat measuring thermometer such as a Bolometer. A thermometer that measured the spectrum and, assuming the emission, (big assuption!) was of a black body, the location of the peak would give the temperature of the emitter according to the Wien displacement law. If the emitter was not a blackbody but let us say atmospheric gases, there are still spectral techniques to reveal the temperature, this is how the surface temperature of Venus was initially determined.

The reason why the 'effective temperature' of Venus is so low (well below that of Earth, even though it is much closer to the Sun) is because the thermal radiation is blocked by the same reflective material that causes the planet's high albedo, the reflective material is just as effective at reflecting the (internal) thermal radiation as it is at reflecting the incident sunlight. --Damorbel (talk) 06:43, 14 December 2011 (UTC)

So what's the problem? Your dislike of effective temperature as a measure doesn't make it wrong. Dicklyon (talk) 06:47, 14 December 2011 (UTC)

So what's the problem? See here:-

1/ effective temperature cannot be found anywhere on a planet.

2/The IPCC uses the 'effective temperature' to represent the "the surface temperature without GHGs".

3/Using the (1 - albedo) formula ensures that here is no place on the whole planet where this figure represents the temperature, it is just the (false) figure achieved by a defective measuring technique. In fact there are no measurements of this 'effective' temperature, it is only a theoretical prediction based on the observed albedo.

Make no mistake, the observed albedo is not a reliable figure because it is not possible to determine what the reflection characteristics of the planetary material are, it is generally assumed to be diffuse i.e. following Lambert's cosine lawbut almost no real surface follows this law, some, like water, deviate very significantly, the actual reflectance is described much more accurately by the Bidirectional reflectance distribution function, but even this has its limitations. --Damorbel (talk) 09:01, 14 December 2011 (UTC)

http://arxiv.org/pdf/astro-ph/0210216v2 , Equation 1 on page 4 — Preceding unsigned comment added by 192.54.176.190 (talk) 14:02, 14 December 2011 (UTC)

1) "effective temperature cannot be found anywhere on a planet", this is true, BUT what name do you suggest for this quantity ? do you want to changes common names adopted in physics/astronomy only because IPCC use a different definition ?

2) BY DEFINITION IPCC works on Earth data. I think that no one in IPCC has try to work on data coming from of Venus, Neptune, HD 209458b or any other planet.

3) "In fact there are no measurements of this 'effective' temperature", again, this is true, BUT what is your intent ? if you don't like this name, please go to IAU and explain your point.

Otherwise it will be more useful for the non educated reader, if you can add a sentence (at the end) where you state that this definition is not applicable on Earth and that it is not a physical measurement in strict sense. — Preceding unsigned comment added by 192.54.176.190 (talk) 14:36, 14 December 2011 (UTC)

I still don't see a problem. There's no IPCC mentioned in the article, so any potential misuse of the concept that they might have is irrelevant. Yes, they could have been more correct by commenting on what the temperature would have been with no atmosphere and a typical surface emissivity value in the long IR band (which is probably more than 0.9, certainly much higher than 1–A); but their simplification is not our problem. Dicklyon (talk) 22:58, 14 December 2011 (UTC)

Then the article should explain what the 'effective temperature' measures i.e. the radiation emitted by a non-black body and its relation to the actual temperature of that body. --Damorbel (talk) 07:24, 15 December 2011 (UTC)

Good point. I added a bit in the lead about the relation to actual temperature. And I made some corrections to the section that implied that internal heating doesn't afffect the effective temperature; it does, but doesn't affect the approximate calculation given. With a star, for example, the effective temperature is all due to internal heating. Dicklyon (talk) 08:04, 16 December 2011 (UTC)

Effective temperature?

155.68.106.162 you made this change http://en.wikipedia.org/w/index.php?title=Effective_temperature&curid=1460629&diff=480622467&oldid=480620530 I suggest it is not clear what is your source and/or justfication for it. Care to explain? Also you are currently anonymous, it is a lot easier for other contributors if you give yourself a name, thanking you in advance. --Damorbel (talk) 06:33, 8 March 2012 (UTC)

What exactly isn't clear? I used a more general form which makes thing more clear i would assume. The new equations show the relations to emissivity, absorption area and emission area that the previous equations didn't. sorry for the delay. you can call me Jack. 71.59.83.12 (talk) 06:27, 15 March 2012 (UTC)

Jack, for one thing, the emissivity estimate of 0.5 might give a better way to estimate the temperature of the Earth, but it's not an "effective temperature"; see the definition again. Your edit seems to be confusing different things, plus it contains unverifiable data (see WP:V). The stuff about areas is interesting, too, but where's a source that supports what you say about it? Dicklyon (talk) 06:36, 15 March 2012 (UTC)

I see what you mean. Chapter 5 section 1 of Quantitative Astronomy by Thomas Swihart uses the equations I used, he calls it Surface Temperature not Effective Temperature. My mistake. I think these equations are useful though and should be incorporated, perhaps we could add it in a section below or an entirely new article? Jack 155.68.165.137 (talk) 22:59, 19 March 2012 (UTC)

Some questions

Could someone answer the questions below which are currently a bit unclear in the article:

• Is the geometric or bond albedo used?
• Why does the ratio between the absorbed and radiated radiation depend on the rotation? And why are they fractions of the full area? I would expect the absorbed area to be that facing the sun/star (as seen from the sun/star) and the radiated area to be the full area. Why is that not the case?

Gunnar Larsson (talk) 11:22, 3 July 2013 (UTC)

This statement:-

The surface temperature of a planet can be calculated by equating the power received by the planet with the power emitted by a blackbody of temperature T.

has no basis in physics. Planets are never blackbodies; and - where is the 'surface' of a planet with an atmosphere? --Damorbel (talk) 17:51, 4 July 2013 (UTC)

Good point. I changed calculated to estimated, which I think is a better representation of the point being made there. Dicklyon (talk) 19:23, 4 July 2013 (UTC)

In answer to the questions: First, it looks like it's the Bond albedo that meets the definition in the article. Second, the area-ratio method came in with this edit, which from what I can tell from snippets follows the newly cited source there. It seems like an odd approach to me; the 1/4 is just the ratio of the area of the absorbing disk and the emitting whole planet, which makes sense when the planet is all at one temperature, which seems to have been assumed already, but if more nearly true when the planet spins relatively rapidly so it doesn't have a cold dark side; if it spins slowly, the effective rediating area is roughly half as much. The area ratio method does make it easy to consider the subsolar point, where the ratio is 1 (same area emitting as absorbing, under the assumption that it can come to equilibrium within a fraction of a day). Dicklyon (talk) 19:53, 4 July 2013 (UTC)

I copyedited that problem with the constant T assumption to make the emitting area thing more comprehensible. Dicklyon (talk) 20:01, 4 July 2013 (UTC)

I've restored the old "Planet" section on calculating the effective temperature of a planet (without the "watts" changes), and tried to clarify the relationship to the new section on estimating surface temperature. Some editors forgot what the article was about. Dicklyon (talk) 23:43, 4 July 2013 (UTC)

Proposed insertion of additional equation for planetary Temperature.

Doing a bit of algebra, I obtain for the theoretical temperature of the planet:

$T=\left({\frac {A_{\rm {abs}}}{A_{\rm {rad}}}}{\frac {1-a}{\varepsilon }}\right)^{1/4}\left({\frac {R}{D}}\right)^{1/2}T_{\rm {eff}}$,

where $T_{\rm {eff}}$ and $R$ are the Sun's temperature and radius, respectively. Any objections to its insertion after the already present equation,

$T=\left({\frac {A_{\rm {abs}}}{A_{\rm {rad}}}}{\frac {L(1-a)}{4\pi \sigma \varepsilon D^{2}}}\right)^{\tfrac {1}{4}}$ ?

(This is much easier to calculate, since the Sun's temperature is easier to look up than its Luminosity. Also, the units are simpler to handle.) --guyvan52 (talk) 01:08, 22 February 2014 (UTC)

Also, I am confused by the capital and lower case letters for albedo. Is A=a? If so, we need to replace A by a (since capital A is already used as area).--guyvan52 (talk) 01:23, 22 February 2014 (UTC)

If you read the section fully you'll find that the capital A's are the areas of absorption and radiation Jhmadden (talk) 00:25, 15 December 2014 (UTC)

okay we have two sections about the effective temp of a planet in one article! I see your point with this equation, it is useful. I'd like to merge the two sections and write them more clearly as well as make the different cases more clear Lambert sphere, tidal lock, etc. and include separate equations for each instead of just using writing. Very commonly people just assume lambert sphere and set the ratio of A's to 1/4 and also no atmosphere and set epsilon to 1 getting the simpler equation so I'll keep the most general form and talk about the limiting cases and provide those equations. sometime in the next few weeks i'll make these changes. sorry for the delay Jhmadden (talk) 23:25, 30 November 2015 (UTC)

Merge needed ?

I think Planetary equilibrium temperature and the "Planet" chapter of Effective temperature are actually the same topic. Also it seems that equilibrium temperature and effective temperature are (at least in this context) the same thing. In my opinion the two articles should either be merged, or at least visible cross referenced. What's currently not good is that "equilibrium" and "effective" temperature are misleadingly defined like they would be different, while actually they are defined by the same formulas (and planetary equilibrium temperature is the same as effective temperature... for planets); in the formulas, the luminosity and albedo are notated (slightly) differently but everything else is identical, like two different people worked independently on two different articles which actually are about the same subject:

http://en.wikipedia.org/wiki/Effective_temperature#Planet vs http://en.wikipedia.org/wiki/Planetary_equilibrium_temperature#Detailed_derivation_of_the_planetary_equilibrium_temperature

-Paul- (talk) 10:43, 22 October 2014 (UTC)

This article is here to stay as the temperature in the elementary formula ${\mathcal {F}}=\sigma T_{\rm {eff}}^{4}$ is defined (by most textbooks) as the 'effective' temperature not the equilibrium temperature so any use of this formula is using the effective temperature whether its for a planet or star. If a student googles to find this info they will search what their textbook says and it will say 'effective temperature'. I'd really like to clean up this article as it is a mess right now (2 sections for planets!). I'll have some time to write things more coherently in the next few weeks. I'll post my revisions in the talk first. Jhmadden (talk) 23:53, 30 November 2015 (UTC)

totally incorrect basic physics

The intro states: "When the star's or planet's net emissivity in the relevant wavelength band is less than unity (less than that of a black body), the actual temperature of the body will be higher than the effective temperature. "

This is totally incorrect on many levels; lower emissivity does not dictate a higher temperature, whatsoever. Net emissivity in a "relevant wavelength" has even less to do with any "actual temperature," even in the most idealized scenario.

Also, clearly, even in the most basic idealized scenario, what is relevant is both the specific nature of both EM spectrum and the spectrally-dependent emissivity where ever absorption and emission can occur. Wikibearwithme (talk) 18:22, 6 January 2016 (UTC)

Teff Hα vs Teff color

Teff Hα vs Teff color is not noted in text. Would be nice to have it noted. Telecine Guy 19:55, 19 July 2016 (UTC)

References

Radiation spread over the surface of a sphere of radius D?

Twice I came across the phrase: "radiation spread over the surface of a sphere of radius D". From the context it is clear that reference is made to an emitting surface, not a receiving surface. But the words "spread over the surface" suggest to me that the surface is receiving.

I propose the phrase be changed to "radiation originating from the surface of a sphere of radius D". Any objections or suggestions?Redav (talk) 04:17, 20 January 2019 (UTC)

The wording is a bit sparse, I agree. The sphere being referenced in either case is the imaginary surface of a sphere with radius equal to the distance between the source and the receiver. Not the radius of the source. For example the energy a star (of radius R) that hits a planet (of radius r) is related to how that energy is distributed on a sphere of radius D, the distance between the planet and star. Jhmadden (talk) 19:38, 23 September 2019 (UTC)

Kelvins vs "Langleys"

What does one mean by surface temperature exactly? The common notion of temperature is associated with the mean motion of particles and molecules and is measured in kelvins (K). This is a thermodynamic temperature. Satellite measurements of temperature using a bolometer, say, gives a radiation temperature which is at best an estimate of the thermodynamic temperature. Are bolometer measurements sufficiently unique to be described as a separate temperature scale? Should the observations be given in "langleys" instead of kelvins to avoid confusion? It might be noted that variations in surface conditions affect heating and observations. Are "langleys" inherently as accurate as kelvins? How might such considerations affect our perception of climate change? Is there an element of deception in using bolometric temperatures for the monitoring and recording temperature changes over time? Or for recording record highs and lows? Jbergquist (talk) 11:54, 25 August 2021 (UTC)