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    • CommentRowNumber1.
    • CommentAuthorTim van Beek
    • CommentTimeJun 12th 2011
    • (edited Jul 2nd 2011 by John Baez)

    A possible blog post about energy balance models, called:

    Putting the Earth in a box

    This may take a while, because I’ll have to look up some nice pictures and also references.

    This is motivated by the first chapters in the book “Slaying the Sky Dragon”, which contains a lot of criticism of the validity of these models.

    Well, Alan Siddons seems to think that all climate models are energy balance models, and that models that describe the rotation of the planet do not exist. Well, anyway, this books shows that it is possible to mistunderstand quite a bit about this simplest of all models, which provides enough motivation for me to write about it.

    • CommentRowNumber2.
    • CommentAuthorTim van Beek
    • CommentTimeJun 12th 2011

    Does anybody know if it is legal to include pictures taken from books? Or does this violate the copyright?

    • CommentRowNumber3.
    • CommentAuthorDavidTweed
    • CommentTimeJun 12th 2011
    • (edited Jun 18th 2011 by John Baez)

    My unofficial, vague knowledge of US/UK copyright law (on the internet things still default to American info without labelling it as such!) It’s generally not legal to take pictures from a copyrighted, in-copyright book and reproduce them, although presumably one is allowed the same exemptions as textual copyright: use for purposes of academic criticism and analysis, review, satire, parody. I don’t know what the status of “links that actually show images is”. (As data, I know 5 years ago a scientific newsletter held up a report of a prominent scientist held up reporting on him receiving an award for a couple of monthly issues while the “amateur” editor found a photo he could identify and get copyright clearance for.)

    If it’s an academic book, you may find original material it draws from (ppt presentations, articles, etc) which aren’t explicitly copyrighted containing the same pictures. What the situation is there I don’t know, but I’d take the view that if they’re academics they care more about exposure and proper attribution than monetary income so might give using images from such sources a go.

    • CommentRowNumber4.
    • CommentAuthorTim van Beek
    • CommentTimeJun 12th 2011

    Thanx, I’ll try to figure out what to do.

    BTW: If anyone would like to add comments, a simple trick used by programmers is to use a specific prefrix, like “Remark John:”. If you use this, I can find your remarks by a simple text search.

    • CommentRowNumber5.
    • CommentAuthorFrederik De Roo
    • CommentTimeJun 13th 2011
    • (edited Jun 18th 2011 by John Baez)

    I’ll try to come with some more scientific comments, but:

    where I have omitted units for clarity. You should not do that in a physics class!

    in my opinion, this is what teachers/blog writers should not do! They should set the example.

    besides, I think it’s more clear if you do write them e.g. ...(279K) 4... \cdot (279 K)^4

    (no pun intended)

    actually mentioning “no pun”, draws attention to the fact that you might have done (so this means that perhaps you want to do so, implicitly). So why not really make a joke “Hot bodies radiate, also in physics” (well, perhaps one that is better than this) or just not mention it at all.

    One more relevant comment: perhaps you could include ozone with carbon dioxide and water, which is often done. (After all, it’s an important chemical component of the atmosphere, and I think energy absorption by ozone is the cause for the stratosphere being stable (potential temperature rises with height) and the stability of the stratosphere influences weather patterns below in the troposphere. Of course, this need not to be mentioned, but just to support my claim that ozone is important)

    I know one experiment called GERB that measures the radiation budget, but there must be a lot more. Perhaps there are references in Kiehl, Fasullo and Trenberth, on Solar radiation

    • CommentRowNumber6.
    • CommentAuthorTim van Beek
    • CommentTimeJun 13th 2011
    • (edited Jun 13th 2011)

    Thanks for your comments, Frederick.

    …in my opinion, this is what teachers/blog writers should not do!

    Good point.

    …actually mentioning “no pun”, draws attention to the fact that you might have done (so this means that perhaps you want to do so, implicitly).

    Good point, but I think I’d rather not make any joke at all, instead.

    …perhaps you could include ozone with carbon dioxide and water, which is often done.

    For some time I have been browsing blog threads, books and articles where objections are formulated on a much more fundamental level, and I’m thinking I should write about that, first. Stuff that can be explained without going into more details of the inner workings of the atmosphere. So, maybe, what I should do is

    a) explain the zero dimensional earth balance model up to the point of the 33 K gap,

    b) explain what “IR backradiation” is, why it does not violate energy conservation or entropy increase, and can have an effect on the average surface temperature,

    c) the next valid question IMO is how big this effect really is, which gets us into considering the amounts of “greenhouse gases” in the atmosphere, and the effect that every component may have. There is the claim, for example, that the backradiation effect is negligible, and that the 33 K gap is explained by adiabatic warming of the atmosphere.

    If all of this ends up as blog posts, then there should be one blog post for a), one for b) and 543 - say - for c). So far, the pictures that I have included are destined for b). And for bullet point b), it is enough if the emission spectra of two greenhouse gases are shown, but not all (but I should mention that there are others).

    It is hard enough to moderate these kinds of discussion with 10 participants in one room. There are a lot of techniques that I know how to handle that situation. Being able to write and draw on a blackboard is an immense help. Moderation these awful blog threads of pro-contra-AGW discussions is a nightmare. I hope that breaking down the whole topic into small steps will help.

    • CommentRowNumber7.
    • CommentAuthorTim van Beek
    • CommentTimeJun 17th 2011

    First draft is finished: It’s about the zero dimensional energy model only, no explanation of downward longwave radiation or one dimensional models, as that would make the post too long.

    • CommentRowNumber8.
    • CommentAuthorFrederik De Roo
    • CommentTimeJun 17th 2011
    • (edited Jun 17th 2011)

    Hi Tim,

    I think it’s great you’re also writing blog posts!

    I’d like to give a few small comments:

    NASA has

    NASA have? (I’m not sure)

    speculation

    I’m not a native speaker but I though this might sound somewhat negative for researchers in that field, what about “hypothesis”?

    Actually it took me a few minutes before I realized that the sentence about “dark matter” was there for a reason, because dark matter doesn’t emit electromagnetic radiation, but that must be my slow mind… (the average reader may make the jump effortlessly ;) )

    that absorbs and therefore also emits

    I suppose it’s obvious here that this is because of thermodynamic equilibrium? (note: this didn’t take me a few minutes, luckily ;) )

    Today the derivation is contained

    this sentence follows naturally if you don’t read the title above, but with the title it doesn’t read very fluently, I think

    for interesting temperatures.

    what do you mean with this? Does Planck’s function change for uninteresting temperatures?

    Since earth sits in empty space

    it’s a bit funny that you show the earth from the moon below ;-)

    We need to account for the fact, however, that the earth receives energy from the sun on one half of the globe only, on the area of a circle with the radius of the earth

    perhaps you could include a link to John’s early blog post about this fact, or to our wiki page of it (I thought there was one, but I don’t find it immediately) I’m not sure if it’s going to be very clear that this leads to the factor of four, for an occasional visitor.

    The albedo does very much depend on the material, it is almost 1 for ice

    perhaps to add for pedagogical reasons: people wear sunglasses because of this, and ice looks white (reflects all colours)

    (but maybe that’s too pedagogical)

    Frederik

    • CommentRowNumber9.
    • CommentAuthorEric
    • CommentTimeJun 17th 2011

    Very nice. +1

    • CommentRowNumber10.
    • CommentAuthorTim van Beek
    • CommentTimeJun 17th 2011

    Thanks, Frederik, I tried to address some of your points. I think it should be NASA in singular, because it is …agency, but I’ll let the natural speakers figure that out. @Everybody: Please feel free to add your questions/remarks/suggestions directly into the text with some prefix, like

    (Frederik: How about including a picture of a cool snowboarder to illustrate that ice is bright?)

    That one is already done, however.

    • CommentRowNumber11.
    • CommentAuthorGraham Jones
    • CommentTimeJun 17th 2011

    Looks good, Tim. Minor suggestions:

    As we can see, a real surface will always emit less radiation than the ideal black body.

    I’m sure you are right that a real surface will always emit less radiation than the ideal black body (though I’d quite like to know why), but it doesn’t follow from one small picture.

    The albedo does very much depend on the material, it is almost 1 for ice.

    I think that should be snow, not ice. Wikipedia says “Snow albedos can be as high as 0.9; this, however, is for the ideal example: fresh deep snow over a featureless landscape. Over Antarctica they average a little more than 0.8.”

    Conclusion: The Case of the Missing 33 Kelvins

    Omit ’Conclusion’ - it reads more like a cliffhanger for the next instalment.

    A reference to an early blog interviewing Nathan would be nice, where the Planck distribution was mentioned, or so I remember.

    The factor of a quarter that Frederick mentioned: yes there was a blog about that. the Azimuth page is http://www.azimuthproject.org/azimuth/show/Solar+radiation

    ’NASA has’ will perturb a few British people. ’NASA have’ will perturb a larger number of Americans.

    • CommentRowNumber12.
    • CommentAuthorTim van Beek
    • CommentTimeJun 17th 2011

    Thanks Graham, I’ve changed the post as you suggested. That should have been fresh snow - which I had in mind, snowboarding on ice isn’t fun - instead of ice, doh!

    I’d really like to use this occasion to link back to some of the blog posts of Azimuth that shouldn’t sink into oblivion. So I’ve added a link to the geometry puzzle and to the first part of Nathan’s interview, where Planck feedback was mentioned.

    • CommentRowNumber13.
    • CommentAuthorEric
    • CommentTimeJun 18th 2011

    I like the article, but for the record, I would support Frederik’s comment about dark matter. The cheap shot is unnecessary and a bit distracting. Is an argument about dark matter really what you want when you publish this? I can imagine that being irritating to some people.

    • CommentRowNumber14.
    • CommentAuthorTim van Beek
    • CommentTimeJun 18th 2011

    Ok, I changed it to “but that does not need to concern us here”.

    Does “speculation” have such a bad connotation? I don’t see any difference to hypothesis, and I also don’t see that this means that people doing research in that topic do anything wrong. But that’s just me, of course. Others have said that the “theory of evolution” is obviously just a “theory” (reminds you of the crackpot index?) and that the very wording is a sign that there is no evidence…

    • CommentRowNumber15.
    • CommentAuthorJohn Baez
    • CommentTimeJun 18th 2011
    • (edited Jun 18th 2011)

    Wow, another blog article from Tim!

    I’m sorry, I’ve been very distracted by the quantum gravity conference I’m at. All my old pals, especially Carlo Rovelli and Abhay Ashtekar and Jerzy Lewandowski and Ted Jacobson, were here for the first week. They’re going away now, so things will be a bit more calm. Just a bit.

    Tim: is Putting Earth into a Box done and ready to go, as far as you’re concerned? If so, I’ll polish it up a bit and post it soon.

    • CommentRowNumber16.
    • CommentAuthorJohn Baez
    • CommentTimeJun 18th 2011
    • (edited Jun 18th 2011)

    I’m really really really happy that you’re writing these blog posts, Tim! There are tons of things I’d love to learn and explain, and I’m completely overwhelmed by the amount of work this would take. I would love to have ten people helping me write blog posts. But getting one person to do it is the best way for other people to get the idea that they can join in.

    A few minor comments:

    1. For English speakers, the title must be changed to Putting the Earth into a box. You can say “Saturn goes around the Sun” or “Mars goes around the Sun”, but you need to say “The Earth goes around the Sun”. Don’t ask why, just look at this.

    2. It makes my job easier if you write blog posts in HTML rather than the markup language used by the Azimuth Wiki, since Wordpress blogs don’t use that markup language so I have to rewrite everything. The Wiki does accept most HTML, with a few annoying exceptions. So, right now I’m translating your blog article to HTML on the Wiki, so you can see how it works. Of course, I’d rather do this secretarial work for you than have you not write blog articles, so I’m in a very weak bargaining position!

    • CommentRowNumber17.
    • CommentAuthorJohn Baez
    • CommentTimeJun 18th 2011

    By the way, if you say it aloud so you can’t read the capital letter, “putting Earth into a box” means “putting dirt into a box”. That could be the reason we add “the”.

    This blog post is a lot like one I’d sort of been dreaming of writing. Start with the basic blackbody! Then, gradually make the model more sophisticated. Excellent!

    More boring small stuff:

    1. Very educated English speakers will know that “ca.” means “circa” and that “circa” is Latin for “about”. However, many intelligent English speakers will not know this, so I’ve changed “ca.” to “about” everywhere. I try to always remember that many readers don’t know English as well as I do. So, I try to speak simply and avoid slang or unusual words. It’s a bit sad, but it’s worthwhile.

    2. I try to be systematic about using boldface for definition and italics for emphasis, except when I’m incredibly excited!!! I also like to attach Wikipedia links to boldface defined terms, so people can get more information about these terms. I’ll do that for a bunch of the terms you introduced.

    • CommentRowNumber18.
    • CommentAuthorJohn Baez
    • CommentTimeJun 18th 2011
    • (edited Jun 18th 2011)

    The end of the blog post would be a lot more satisfying if we worked out the temperature of a spaceship with the highest easily obtained albedo orbiting the Sun near Mercury. I’m actually surprised at Tim’s claim that we won’t “fry”. (But I don’t know what temperature counts as “frying”.)

    What’s the highest albedo of white paint? Does this albedo apply to the infrared range or only visible light? Even if we can’t figure this out, we can make a guess… people on the blog will enjoy discussing it.

    I think magnesium oxide and titanium oxide have the highest albedos in the visible range.

    • CommentRowNumber19.
    • CommentAuthorJohn Baez
    • CommentTimeJun 18th 2011
    • (edited Jun 18th 2011)

    You use the term “energy flux” without defining it right away. Over on Wikipedia we see lots of terms like ’irradiance’, ’radiance’, radiosity’, ’radiant flux’, ’radiant intensity’, ’radiant excitance’, etcetera, most of which mean different things. It sounds like you mean irradiance. Personally I don’t mind “energy flux”, but the crucial thing is to say what it is: power per area.

    [Edit: never mind, you did define it.]

    • CommentRowNumber20.
    • CommentAuthorJohn Baez
    • CommentTimeJun 18th 2011
    • (edited Jun 18th 2011)

    Here’s an example of that business about needing a semicolon when a sentence is actually made of 2 or more grammatically complete sentences:

    Real bodies don’t have this property, instead they absorb radiation at certain frequencies better than others…

    This should be:

    Real bodies don’t have this property; instead they absorb radiation at certain frequencies better than others,

    with perhaps a comma after “instead”, though commas are very hard to agree on.

    • CommentRowNumber21.
    • CommentAuthorJohn Baez
    • CommentTimeJun 18th 2011

    By the way, “watt”, “kelvin” and other units named after people are not capitalized according to SI conventions.

  1. John said:

    we see lots of terms like ’irradiance’, ’radiance’, radiosity’, ’radiant flux’, ’radiant intensity’, ’radiant excitance’, etcetera, most of which mean different things.

    in case this is going to be worked out on this wiki too, I’ve already made a preliminary start on the page Atmosphere

    • CommentRowNumber23.
    • CommentAuthorTim van Beek
    • CommentTimeJun 18th 2011
    • (edited Jun 18th 2011)

    John asked:

    Tim: is Putting Earth into a Box done and ready to go, as far as you’re concerned? If so, I’ll polish it up a bit and post it soon.

    Others have already helped. I waited for your feedback; once we agree on the final version it is ready to post.

    The end of the blog post would be a lot more satisfying if we worked out the temperature of a spaceship with the highest easily obtained albedo orbiting the Sun near Mercury.

    I wasn’t sure if I should calculate that myself or leave it open, implicitly as it is now, or explicitly by asking “can you calculate it”? Of course you, John, would jump at such a question right away, anyway :-)

    So you think I should look up the paint with the highest effective albedo? (Or whatever the albedo is called that reflects the most given a radiation proflie.)

    Edit: I think I won’t look it up myself but will let it stand as an explicit question as it is now.

    • CommentRowNumber24.
    • CommentAuthorTim van Beek
    • CommentTimeJun 18th 2011
    • (edited Jun 18th 2011)

    John wrote:

    Over on Wikipedia we see lots of terms like ’irradiance’, ’radiance’, radiosity’, ’radiant flux’, ’radiant intensity’, ’radiant excitance’, etcetera, most of which mean different things.

    These should be well defined; I looked it up “atmoshpere and radiance” textbook I mentioned before.

    Of course, I’d rather do this secretarial work for you than have you not write blog articles, so I’m in a very weak bargaining position!

    Oh, come on…

    Unless there is still something wrong with the syntax, I’d say it is ready to be posted.

    • CommentRowNumber25.
    • CommentAuthorJohn Baez
    • CommentTimeJun 19th 2011

    Okay, I’ll work on it more and post it soon. Yesterday I was taking key terms and adding links to Wikipedia, but then Lisa wanted me to go out an explore Zurich (which was indeed nice). I’ll finish adding links today. I also need to take all the images and turn the links into HTML links. I may also change your explanation of “energy flux” a bit - right now I think you define energy flux per wavelength before defining energy flux, but I think it’s easier for people to understand the total energy flux first. A small rewrite.

    Also, I agree that’s it’s better to make the calculation of the temperature of a very white rocket near Mercury into a challenge! I may take up that challenge on the blog.

    • CommentRowNumber26.
    • CommentAuthorJohn Baez
    • CommentTimeJun 19th 2011

    By the way, as Tim marches forwards he may want to compare his discussion to this article by Chris Colose, and various related articles by Colose.

    • CommentRowNumber27.
    • CommentAuthorTim van Beek
    • CommentTimeJun 19th 2011

    Will do. I had to write about the zero dimensional energy balance model for my own sanity after reading “Slaying the Sky Dragon”.

    Writing about the Milancovich cycles, snowball earth and stochastic resonance will be slightly more interesting and original.

    I also need to take all the images and turn the links into HTML links.

    Ok, I’ll see how that is done. One needs to first upload the picture to the Wiki, right? It has to be stored somewhere.

    Lisa wanted me to go out an explore Zurich (which was indeed nice)

    Did you talk to some original Switzerlanders? (There are a lot of Germans in Switzerland right now, because they pay much more money for most jobs where one needs a good education.) Did you notice that they speak waaaayyy more slooooowly than other Europeans?

    • CommentRowNumber28.
    • CommentAuthorJohn Baez
    • CommentTimeJun 19th 2011
    • (edited Jun 19th 2011)

    We need references or (better) links for all pictures that contain information, not for copyright purposes but just so people can check the source of that information. So, Tim: could you tell me where you got that picture of planetary orbits and temperatures? I can’t find it online.

    I’ll go ahead and post the blog article now if I get it done in time - I’ve got limited time this weekend, because I’m supposed to be acting like a tourist. I can add the link later.

    • CommentRowNumber29.
    • CommentAuthorTim van Beek
    • CommentTimeJun 19th 2011

    It’s from the NASA report mentioned at the bottom of the page, where I wrote “whenever I wrote NASA, I actually referred to…”

    • CommentRowNumber30.
    • CommentAuthorJohn Baez
    • CommentTimeJun 19th 2011
    • (edited Jun 19th 2011)

    More small comments:

    "Centigrade" is not the official SI name, it’s "Celsius". I usually write things like 18 °C for temperatures in Celsius. I believe this is correct. I try to get these details right because I figure part of my job is to set a good example.

    This is not a coincidence, the black body is by definition the body that generates the highest energy flux at a fixed temperature.

    Here’s another example of a ’sentence’ that’s really 2 complete sentences; in English this needs to become:

    This is not a coincidence; the black body is by definition the body that generates the highest energy flux at a fixed temperature.

    or, in this particular case, even better:

    This is not a coincidence: the black body is by definition the body that generates the highest energy flux at a fixed temperature.

    since the latter portion explains the former. (The rules about colons versus semicolons are a bit hard to explain, but I seem to know them intuitively.)

    I changed the article’s title to

    Putting the Earth in a box

    since ’into’ seems slightly awkward here. It took me a while to realize this: it’s easier for a native speaker of a language to pick the best choice of words than to notice that the second-best choice is not quite optimal!

    • CommentRowNumber31.
    • CommentAuthorJohn Baez
    • CommentTimeJun 19th 2011
    • (edited Jun 19th 2011)

    By the way, I know all my remarks above are boring and annoying. These are the pedantic things I think about when I’m writing - I don’t usually bother talking about them. I’m only mentioning them now in case someone wants to write a lot of posts on the Azimuth Blog and wants to make my life really easy.

    But I’d much rather get posts and make these small changes myself than not get posts! So please ignore my remarks if you like — and whatever you do, don’t use them as an excuse to not write blog posts!

    • CommentRowNumber32.
    • CommentAuthorJohn Baez
    • CommentTimeJun 19th 2011
    • (edited Jun 19th 2011)

    Okay, I published Tim’s blog post!

    Putting the Earth in a box

    I think this is a really great post, because:

    1. it combines facts with enough digressions to make it fun, but not so many that the point becomes obscure;

    2. it includes enough technical detail to be precise, while not including any unnecessary detail;

    3. it defines all the technical terms it introduces.

    Almost anything in science is interesting if it’s explained correctly, but most people haven’t learned how to explain things correctly, and they often violate rules 1-3.

    To implement rule 1, you need to be very clear about what you’re trying to accomplish. What is the main point?

    To implement rules 2 and 3, you need to form a clear mental model of your audience and stick to it. This is where most people do a bad job.

    For example: if your intended audience is people trying to learn the most basic concepts of group theory, you need to define of ’group’. Most people explaining math understand this. But they often forget that you also can’t use the term ’additive group’ without some explanation. Everyone who understands group theory takes this piece of jargon for granted, so it’s easy to forget that it’s completely mysterious to people who don’t yet understand group theory. Knowing what the words ’group’ and ’additive’ mean is not enough to understand a sentence like ’consider the additive group of real numbers’.

    The only solution is to carefully go through what you write, look at each phrase, and think about whether your intended audience will understand it. I do this automatically by now (with some mistakes of course), but lots of people don’t even think about doing it.

    Tim seems to be doing it pretty consistently, and that’s great.

    Of course, his post does assume the reader will understand integrals. This could have been avoided by skipping the part about ’monochromatic energy flux’ and the Planck distribution and going straight to ’energy flux’ and the Stefan-Boltzmann law.

    However, you can’t get too far in climate science without learning that different frequencies of radiation interact with the atmosphere, etc. in different ways. And you can’t get too far without calculus, either! So, it’s probably fine to assume an audience who knows calculus.

    • CommentRowNumber33.
    • CommentAuthorTim van Beek
    • CommentTimeJun 19th 2011
    • (edited Jun 19th 2011 by John Baez)

    You have no idea how much work it is to write a 200 page system specification and discuss this through with 50 people with widely differing backgrounds and interests, including people who’ll simply say “I’ll cast my veto because I did not like the whole topic from the very start. We should have done what I said 5 years ago from the very beginning!”

    • CommentRowNumber34.
    • CommentAuthorJohn Baez
    • CommentTimeJun 19th 2011
    • (edited Jun 19th 2011)

    You have no idea how much work it is to write a 200 page system specification and discuss this through with 50 people […]

    No, I don’t — and I hope I never do!

    But this may explain why you seem mysteriously better at explaining things than most people. You probably have some mental model of your audience, and potential critics. A lot of scientists seem to write while thinking very hard about the subject material and not at all about the audience. They are basically writing to themselves. That’s deadly.

    • CommentRowNumber35.
    • CommentAuthorTim van Beek
    • CommentTimeAug 25th 2011

    I am very glad that we can have the kind of discussion happening between John and Dermod O’Reilly on the blog. This seems to be some kind of “unique selling point” for Azimuth, being well informed and civil. After surfing the web for several months I cannot imagine that this could happen anywhere else.

    Nevertheless I’m a little bit surprised that the concepts of “equillibrium” and “steady state” seem to be a problem, and that some people believe that the temperature difference of 33 K in the 0-dimensional energy balance model seems to be the heart of the “greenhouse effect”, something like

    First people calculate a 33 K gap and then postulate that there has to be some obscure greenhouse effect to explain this gap. If one finds a fatal flaw in the energy balance model, the greenhouse effect is debunked.

    Maybe a follow up post (a follow up to “a quantum of warmth”, that is) should address these issues.

    • CommentRowNumber36.
    • CommentAuthorJohn Baez
    • CommentTimeAug 26th 2011

    Tim: I’m glad you enjoy this “civil discussion” aspect of the Azimuth blog.

    I am not especially surprised that somebody doesn’t know the difference between “equilibrium” and “steady state”. I don’t mind explaining such concepts, because I’m sure many of our readers (who come from a wide variety of backgrounds) haven’t thought much about thermodynamics.

    Azimuth should ideally contain a mix of “educational” and “new research” posts, but since I’m just getting started in my new career, and busy learning lots of basic stuff, it’ll start out being mainly “educational”.

    Maybe a follow up post (a follow up to “a quantum of warmth”, that is) should address these issues.

    That would be great! That post you had partially written on “downward longwave radiation” might be one place to address them.

    • CommentRowNumber37.
    • CommentAuthorFrederik De Roo
    • CommentTimeAug 26th 2011
    • (edited Aug 26th 2011)

    Tim wrote:

    I am very glad that we can have the kind of discussion happening between John and Dermod O’Reilly on the blog. This seems to be some kind of “unique selling point” for Azimuth, being well informed and civil. After surfing the web for several months I cannot imagine that this could happen anywhere else.

    Yes, it was really civil.

    What surprized me was that our reader did not want to compare thermodynamic effects at different length scales. And I can’t understand how he could answer to Tim that absorptivity and emissivity play a role in designing spacecraft, while at the same time commenting in another sub-thread:

    All I am saying is that neither the emmissivity, the absorptivity nor the scattering coefficients have any influence on the equilibrium temperature reached by any material in an electromagnetic radiation field – it would be contrary to the 2nd law of thermodynamics.