Talk:Solar radiation

From Wikipedia, the free encyclopedia

[edit] Mention of Insolation

Insolation is mentioned and a global quote is given as 342 W/m^2. However, insolation is never given in W/m^2. Instead, it is given as a measure of energy, and therefore in kWh/m^2. Even the link to the insolation page says as much. Kopasa 13:51, 19 June 2007 (UTC)kopasaKopasa 13:51, 19 June 2007 (UTC)

In fact, I'm fairly certain that the distribution across the cross-section is an incorrect calculation. It really makes no sense and to quote the DoE website "The radiation that reaches sea level at high noon in a clear sky is 1000 W/m2", and the solar constant is given as 1367 W/m^2 with no mention of a distribution across the cross-section. Kopasa 12:56, 20 June 2007 (UTC)kopasaKopasa 12:56, 20 June 2007 (UTC)

I removed the section pertaining to the incorrect insolation reference. Kopasa 13:01, 20 June 2007 (UTC)kopasaKopasa 13:01, 20 June 2007 (UTC)

Hmm. 342 is correct, and the page explains why. Expressing it in w/m2 is also correct. Calling *only* this insolation is odd though William M. Connolley 13:04, 20 June 2007 (UTC)

342 is correct answer for a calculation that is incorrect. the incident solar radiation is not averaged over the cross-section to find the insolation. all refs (including the one i used above, the Dept. of Energy) use the solar constant as a measure of the energy incident on any portion of the upper atmosphere.

also, calling the answer the insolation is incorrect, as even clicking the link to insolation will show. insolation is a measure of solar energy, and is measured in the SI joule/m^2, or the more standard kWh/m^2. calling this solar irradiance would be more appropriate, and would be 1367 W/m^2 for the top of the atmosphere, and ~1000 w/m^2 for the surface of the earth.

This all said, deletion of this misleading calculation is highly recommended. Kopasa 13:50, 20 June 2007 (UTC)

I strongly disagree: that the average solar flux at TOA is 342 is well worth noting. Whether we call it insolation or not I care little about. I would call it insolation; and I would measure it in w/m2 not w/m2.s. I doubt there is uniformity over this William M. Connolley 13:57, 20 June 2007 (UTC)

If you had ever read anything else on solar energy, you would be very aware of this difference and how misleading it is. perhaps you would also be aware of the constant uniformity of the terminology in regards to research on the subject. the calculation is one i have not seen reproduced anywhere, so a single reference to its validity would be appropriate. until then, it remains mislabeled and therefore greatly misleading.

That said, i do agree that calling it the average flux, making sure to note that this calculation includes the half of the planet not receiving radiation from the sun, would be appropriate. Kopasa 14:16, 20 June 2007 (UTC)kopasa

made a few changes taking into account the terminology discrepancies as well as deleting a redundant initial sentence whose entire content had been covered but the final sentence of the preceding paragraphs. hope this is better! Kopasa 14:58, 20 June 2007 (UTC)kopasa

[edit] Confusion

Because the surface area of a sphere is 4 times the surface area of its cross-section, the temporally and spatially averaged insolation over the Earth's surface above the atmosphere is a quarter of this value, 342 W/m²

I can't for the life of me understand this sentence. Does cross section mean diameter, this is the first mention of insolation and could it be replaced with "incoming solar radiation (insolation)"? I don't know much about this so I thought I'd best leave it alone but could someone please change it? I've put a heading on a previous talk topic, if this is offensive feel free to delete it. Rex the first 23:43, 20 December 2005 (UTC)

Do the changes I've made make it clearer? Dragons flight 00:16, 21 December 2005 (UTC)

I thought my sentence was a model of concision and clarity :-) To be picky,

The Earth recieves a total amount of radiation determined by its cross section (π R²), but averaged over time this energy is distributed across the entire Earth's surface area (4 π R²).

is slightly misleading, in that: averaged over time this energy is distributed across the entire Earth's surface area implies (to me) even distribution; averaged over time the insolation is uneven wrt latitude. William M. Connolley 09:50, 21 December 2005 (UTC).

I think the newer edit makes more sense but maybe you could add "even though the insolation is uneven wrt latitude" or something like, thanks anyway! Rex the first 16:06, 21 December 2005 (UTC)

(Recent comment about 10^17 W moved to new section further down. Han-Kwang (t) 00:47, 15 November 2007 (UTC))

[edit] Cold and hot countries edits

(next two items are copied from user pages)

"In cold countries most people like sunshine and prefer not to be in the shade. In hot countries the converse is true and the midday hours people preferably stay inside, because it is too hot to go out."

I dont mean to sound arrogant or anything, but I dont think adding that to the article about Solar radiation was a very relevant contribution. What you wrote was your opinion and it is fine, but an encyclopedia should have non-biased factual information. Again, I hope you dont take it offensively, but I have removed it.

Nice to see kind people on wikipedia contributing to articles, and you seem to have done alot of good work.

Jedi Dan 16:39 Apr 23, 2003 (UTC)

I had my doubts about Patrick's addition at solar radiation too, and at first the only reason I put it back in after the edit conflict was because I know he generally does good work, and wouldn't put something like that in just to be a smart aleck. Then, figuring there must be some reason for what he did, I checked the "What links here" for that page, and sunshine is, sure enough, a redirect to solar radiation, so I would think he'd put that in there for people who followed that redirect to get there. -- John Owens 16:52 Apr 23, 2003 (UTC)

Adding to that, actually, it seems to me that Patrick's contribution is possibly even more relevant. After all, most of the current content is about the solar fusion that produces the radiation, than the radiation itself. Don't get me wrong, I love knowing more details about the process, but Patrick's bit is at least as relevant to the article title (and especially the redirect) as Jedi Dan's. Now that I see that solar fusion doesn't exist yet, perhaps some of this could be moved there? Or moved into fusion, and make solar fusion a redirect to that? -- John Owens 17:13 Apr 23, 2003 (UTC)

There is already quite about about fusion at Nuclear_fusion and my article was meant to really be an overview about fusion and how it relates to solar radiation rather than anything in depth about the process. I suppose I perhaps put a bit too much irrelevant information in myself, I dont mind if someone wants to reorganise things or move it about.

Jedi Dan 23:19 Apr 23, 2003 (UTC)

[edit] Moving stuff to Nuclear fusion

(William M. Connolley 20:37, 24 Jul 2004 (UTC)) I removed a load of stuff to nuclear fusion which I thought was fair... but I'm willing too be disagreed with.

[edit] Carcinogen

Just a note that solar radiation is brought up as a IARC Group 1 carcinogen in the list there, but there's no talk about its carcinogenic nature to humans here about UV light exposition. This article is also not member of the Category:IARC Group 1 carcinogens category. I'm not sure of in which extent this information should be added though, so I'm just bringing it up here as a heads-up for now. I'd probably expect to read something about the solar radiation risks to humans here, although I'm not sure it's actually supposed to be in the Group 1 Carcinogen category and all. -- Jugalator 02:41, 22 December 2005 (UTC)

Perhaps there should be a section on the biological effects of various parts of the spectrum. (SEWilco 07:58, 23 December 2005 (UTC))

[edit] Merging Sunlight

Opposed: Solar Constant and Solar Radiation are close enough to each other to warrant merging. However, Sunlight is clearly a distinctively different subject. It is the sort of article that a six-grader would go to for information on the nature of sunlight. Trying to merge a scientific discussion of the solar constant into Sunlight is unwarranted. What should ocurr is Solar constant should be expanded with all the information from Solar radiation and Solar radiation should be tossed. This way, you have two distinctive topics: Sunlight and Solar constant. Greg L 17:25, 24 October 2006 (UTC)
Oppose: Keep the solar radiation technical and the sunlight non-technical, with directs to solar radiation for details.+mwtoews 20:14, 29 December 2006 (UTC)

[edit] Merging Solar constant

Agree: Solar Constant and Solar Radiation are close enough to each other to warrant merging. Greg L 17:25, 24 October 2006 (UTC)
Agree: Similar content; same physics.+mwtoews 20:14, 29 December 2006 (UTC)
Disagree: Isn't this constant important enough to warrant its own article? Also what about Sun unit? —Preceding unsigned comment added by 141.213.247.14 (talk) 22:10, 8 October 2007 (UTC)

Solar Constant values being associated with "winter" and "summer" is silly. Who's summer or winter is being referenced? The larger value is associated with the Earth reaching perigee and the smaller value with Earth reaching apogee in its orbit around the sun. 67.166.28.214 21:28, 13 April 2007 (UTC)

[edit] Effect on Climate

The first paragraph of this section does not really address the question of how solar variability affects climate. To me it could be left out and nothing would be lost. Birdbrainscan 05:16, 27 January 2007 (UTC)

[edit] Sunfall

Notwithstanding the prior use of this word in connection with a series of novels, I think that the cummulative total of radiant energy incident per unit area over a stated time should be termed "sunfall" by analogy with the term "rainfall".

The obvious units (solar full spectrum) are joules per square meter per second, but a better term might be, "apollos", for example. —The preceding unsigned comment was added by 70.157.183.102 (talk) 03:07, 16 February 2007 (UTC).

We don't invent terminology here. Got a published description of a unit of measure? (SEWilco 04:19, 16 February 2007 (UTC))

[edit] Langley's Solar Constant

Am wondering if the reports of Langley's solar constant could be clarified. The value of 2.54 cal should be cal/min/cm^2. The per minute per cm^2 part seems to be missing. The current value of 1366 W/m^2 of the main text translates to 1.958 cal/min/cm^2, consistent with other information, including the picture explanation Skeptiker 22:57, 16 February 2007 (UTC)

Fix it. I think "2.54 cal" was in the source material, which was a summary which probably assumed the rest. (SEWilco 04:32, 17 February 2007 (UTC))

Fixed! Hertz1888 02:37, 22 July 2007 (UTC)

[edit] Solar irradiance spectrum above atmosphere and at surface

This is a very nice graph -- would be even nicer if someone could add bounds for the visible portion, and label the UV and IR ends, for us casual browsers.-69.87.199.249 12:49, 10 May 2007 (UTC)

Even better would be to annotate also with a color bar, for the visible part.-69.87.203.17 20:03, 27 May 2007 (UTC)

I am curious why this page includes two graphs of solar irradiance at TOA. I have my doubts about the top one. Second one shows peak irradiance in visible range where it belongs, the top one shows peak in infrarad range. Don't understand the author's comments about shifting peak due to change in variable, is it possible bad "line by line computations" occurred during this step? -Wjifkri Wjifkri 21:39, 5 September 2007 (UTC)

If you look closely, you will see that the upper graph is plotted as intensity versus wave number (the reciprocal of wavelength, analogous to frequency), and the lower graph shows intensity versus wavelength. The horizontal units and linearity are different, and infrared is to the left on the upper graph, to the right on the lower one. Not bad computations at all, just two different ways of presenting the data, making direct comparison a bit awkward. Presumably each way has its advantages. Someone else will be better able to explain that aspect. I hope this helps. Hertz1888 23:24, 5 September 2007 (UTC)

I noticed the change in variables and understand the inverse relationship of frequency and wavelength. Not surprised that graph experiences some changes, however, the sun does not shine differently because a different variable is used. Why should the peak move from visible range (.5 micron, wavenumber 20000) to infrared (1 micron, wavenumber 10000)? Wjifkri 14:25, 6 September 2007 (UTC)

That's because the surface under the graph has to be conserved. For example, the area between 400 and 600 nm only spans 200 nm, but it corresponds to a span of 8333 1/cm. On the other hand, the range 0-1000 cm-1 corresponds to an infinite wavelength range starting at 10000 nm. In order to preserve ratios of surfaces under these two intervals, the curves have to be adjusted, which also changes the peak position. Formally:

$I(\lambda) d\lambda = I'(\nu) d\nu = I(1/\nu) |\frac{d\lambda}{d\nu}| d\nu = [I(1/\nu)\frac{1}{\nu^2}] d\nu,$

where I is the curve in wavelength units, and I' the curve in inverse-wavelength units. Han-Kwang (t) 21:57, 6 September 2007 (UTC)

I got it now. Took the time to work out some points to get a feel for the numbers. Should have done that first. Thanks to all and sorry for the distraction. Wjifkri 04:18, 7 September 2007 (UTC)

[edit] data sources

Where can one find real-time solar radiation data for any spot on the surface of the Earth? Where can one find online calculators that take location date and time as input and output predicted-modeled-average and predicted-modeled-maximum.-69.87.203.17 20:03, 27 May 2007 (UTC)

"Pysolar is a collection of Python libraries for simulating the irradiation of different parts of the earth by the sun.

As of June 3, 2007, it has two parts:

A library that, given a date, time, and and earthly location, calculates the location of the sun
A library that, given a panel spacing and dimensions, calculates the shading percentage as a function of time for a row of 2-axis tracked panels"

[1] -69.87.200.198 00:21, 6 June 2007 (UTC)

[edit] Anon edits

Re this [2]: This would suggest the energy from solar power is enormous. is just too colloquial. Solar radiation reaches the Earth's upper atmosphere at a rate of 1366 watts per square meter (W/m2) has already been said higher up in the article. The bit about fission reactions is WP:OR and not obviously relevant William M. Connolley 13:52, 17 June 2007 (UTC)

The most recent version also indicated that the author has no idea how many atoms are involved in a nuclear reactor's activity. (SEWilco 13:58, 17 June 2007 (UTC))

Removed again. There is already an estimate of the total power flux, higher up, which is more meaningful than a count of unspecified "nuclear collisions". --Heron 14:49, 17 June 2007 (UTC)

[edit] Total?

It would be helpful to have a number of total solar radiation that hits the earth in 24 hrs. Not in units of power, but in units of total energy (joules?)

13?? * pi * r^2 * 86400 (j/s/m2 * m2 * s = j) William M. Connolley 16:34, 16 July 2007 (UTC)

Ah, thats above the atmosphere, of course William M. Connolley 16:34, 16 July 2007 (UTC)

[edit] Solar irradiance per capita

A value of 6000 W for total solar energy reaching the earth's atmosphere "per human on the planet" was added to the article, together with a reference citation giving global average energy consumption as 2000 W per capita. Evidently (tell me if you disagree), a gross calculation error was made, and I have undone this edit. From the Earth article we obtain a surface area of 510 E06 sq. km = 5.1 E14 m2. Multiply by 342 W/m2 and divide by world population of 6.6 E09, and the result is ~ 26 MW (Megawatts) per capita. Alternatively, the earth's cross-section intercepts 1.74 E17 W, per the solar constant section. Divide this figure by 6.6 E09, and the result is the same, ~ 26 MW per capita. Present energy needs for the entire planet would be met by the solar energy incident on one of the smaller countries or American states, properly harnessed. Hertz1888 01:47, 3 August 2007 (UTC)

Sorry, my bad. I did the calc and came up with a "wow" number, but unfortunately I had used 6E12 instead of 6E9 for the population. 7 years working for an engineering company seems to have fried every brain cell connected with math. I swear they're making me senile. AllGloryToTheHypnotoad 19:10, 3 August 2007 (UTC)

Brain fog is not uncommon, AllGlory; I wish you a complete and speedy recovery from yours. Speaking of "wow" numbers, the quantities here - and all other astronomical numbers - are so mind-boggling, it's hard to imagine how any human can handle them. Manipulate, yes, but truly grasp? And yet (a thought for the day), as far as we know, human consciousness is the best resource the universe has for being aware of itself! Hertz1888 04:31, 4 August 2007 (UTC)

Give the human race twenty thousand years and a few near-extinction events, and maybe. But right now we're still just mammals with a tool-making fetish. We're still picking fleas off each other and stealing each other's fruit. AllGloryToTheHypnotoad 17:25, 4 August 2007 (UTC)

[edit] how much of solar radiation is heat?

From what I've heard, the 1,366 W/m² of solar radiation consists of light (both visible and invisible) and heat. However, does anyone know exactly what percentage of the solar radiation received by the Earth is heat? I found a source saying that 60% of solar radiation is heat, but another editor said that it was incorrect. --Ixfd64 01:15, 14 September 2007 (UTC)

What I said was that the cited source was restricted (inaccessible)-- Wiki discourages referencing sites needing login -- and that the statement was vague. This is because giving a percentage of the total solar radiation that is heat is far from a simple matter. It depends on how heat is defined (and transferred and absorbed). There are a variety of definitions of heat, none necessarily leading to a specific percentage of solar energy. Giving a percentage without properly defining the conditions would not be encyclopedic. Hertz1888 01:54, 14 September 2007 (UTC)

Are you talking about this link? This is strange; I wasn't asked to log in when I accessed that site. I'm guessing that certain IPs (the one I'm using right now belongs to the University of California, Berkeley) are automatically granted access. --Ixfd64 02:48, 14 September 2007 (UTC)

Correct. This is as far as I (an off-campus user) can get: "Access Restricted"... "This article is available through Project MUSE, an electronic journals collection made available to subscribing libraries." How does the article define heat? Distinguish it from light? Hertz1888 03:05, 14 September 2007 (UTC)

The article said that "sixty percent of solar radiation is transmitted through heat." Other that that, there isn't any other relevant information. Come to think of it, that article probably isn't a very reliable source at all. --Ixfd64 03:53, 14 September 2007 (UTC)

[edit] Number in W

I am having some confusion about the number 1.740×1017 W. Is that per min, hour, day? Please, this would help greatly. 75.60.172.81 00:38, 15 November 2007 (UTC)

W is watts, that is joules per second. Han-Kwang (t) 00:47, 15 November 2007 (UTC)

[edit] ...1366...?

How convenient that my comments were lost in the merger:
Once again, where is the specific reference for this specific (phony) value...1366 W/m²
I am not siting this as a better reference, just pointing out the discrepancy: ["1367.8204W/m²"]
GabrielVelasquez (talk) 06:36, 5 January 2008 (UTC)

You don't state what you're doing in those calculations. Are you calculating how much energy the Sun is emitting across its disk and then the fraction of that energy which the Earth intercepts? Are you accounting for how much energy is blocked by passing at various angles through the Sun's photosphere and corona? The energy absorbed by solar wind particles? There are undoubtedly other unknown factors. Is the number which you disagree with based upon theoretical calculations or measurements at the Earth? Measurements are more likely to include unknown factors and correspond better to reality. -- SEWilco (talk) 16:53, 5 January 2008 (UTC)

I find it cute when people miss the point (airplane sound overhead). Here, I'll copy this over from Talk:Insolation, and I hope it helps. Also you counter measurements with measurements, those are the calculations of professional scientist, I just did a little basic algebra.GabrielVelasquez (talk) 20:46, 5 January 2008 (UTC)

The reference is right there in the article (ref. 1), and pertains to measurements made during the last three solar cycles. An average value of 1366 units (to the nearest whole number) is clearly visible in the concluding graphs (Figures 4 and 5). I think you are preserving more decimal places in your results, and possibly attaching more importance to those extra digits, than is justified by the accuracy of the observational data. The value for R, for example, has only three significant figures (without taking into account the uncertainty of the measurement, which may degrade the accuracy further).

In the solar constant article, it says roughly 1366 W/m², and I am going to add the same word to this article. I hope this response helps. Hertz1888 (talk) 05:06, 2 January 2008 (UTC)

My-god-man, I almost needed a magnifying glass for that. And you had to actually point it out. Couldn't you place that "figure 4 and 5" below with/next-to the link for that article. And incidentally, why are you rounding up? - Just kidding.
I did shift the [1] over to the number itself.
thanks, GabrielVelasquez (talk) 07:01, 5 January 2008 (UTC)

Look at the Solar variation article, in particular the graph there. You see that it varies from about 1365.5 to about 1366.5, if you use the smoothed values; or rather more if you take the instantaneous values. Your error is to assume that your value for the sfc T of the sun is accurate. Try seeing how much you need to vary it to get down to 1365.5 - I would guess its very little. Oh,a nd I should also add that the graph is a bit misleading, because its a patchwork of different satellites, and their absolute calibration is a problem William M. Connolley (talk) 20:52, 5 January 2008 (UTC)

Ummm, the effective temperature of the sun is a derived number based on measuring the solar constant, not the other way around. If you want a highly accurate solar constant, then using a derived temperature without any specified source or uncertainty is not the way to go about it. Dragons flight (talk) 21:20, 5 January 2008 (UTC)

Ooowah, point taken: I know this isn't the place to ask this, but since you seem to know, I'm not still wrong in calculating HZ median Solar Constant distances for other stars with that formula?? f=(R²aT⁴)/(d²), from L=4π·R²aT⁴, and L=4π·d²f.
GabrielVelasquez (talk) 22:05, 5 January 2008 (UTC)

[edit] Terrible graphs

The article has three graphs, all of them different. We start with one of rather high detail but low quality; it uses the term "wavenumber" and other language that makes me think it was converted from another language. The next graph clearly states it is inaccurate, yet it has a rather prominent location in the article. Finally the third graph seems to be clear, and readable, yet uses a different set of axes that makes comparison difficult.

Surely we can do better?

Maury (talk) 15:16, 28 January 2008 (UTC)

Agreed. Anyone willing to have a go? Think outside the box 17:20, 1 February 2008 (UTC)

[edit] Loaded Sentence

"When ultraviolet radiation is not absorbed by the atmosphere or other protective coating, it can cause a change in human skin pigmentation."

A much more scientifically concise and accurate approach would be:

"When ultraviolet radiation is absorbed by the skin it can cause changes in pigmentation (relevant link). Various factors (duration of exposure, column ozone, air quality, weather, season, latitude, clothing, and other protective measures [with links where relevant]) affect actual solar ultraviolet exposure to the skin."

This, of course, assumes that a discussion of skin pigmentation belongs here.

Also - solar radiation is *white* to our eyes. Buy a yellow bulb, switch it on in and otherwise dark room and look at a white peice of paper - you will see the color yellow. Take that same peice of white paper out into direct sunlight - the paper will appear *white* not yellow. The solar spectrum at the surface is nearly flat from 450 nm to 650 nm and in the strictest sense is actually a bit stronger in the green (to which our eyes are more sensitive) than the yellow, but since our eyes are logarithmic detectors these subtle variations are not distinguishable. Sunlight is "white".

65.202.227.93 (talk)mjd 2008.04.11.10:28EDT —Preceding comment was added at 14:29, 11 April 2008 (UTC)

Solar radiation really is white. I didn't make that up. There is a common misconception that it is yellow due to two equally deceptive phenomena. The first, everyone tells you it's yellow - so you are predisposed to think so. Few ever actually try to stare at the sun to figure out what color it is for themselves (kids, don't try this - looking directly at the sun is bad for your eyes - that's why one should intuit the sun's color from the color it casts on a white object - which is white). Second, even if you try to take a look for yourself, looking at a dazzlingly white object on a very deep purple-blue (anti-yellow-orange) background can give the impression of a yellowish sun if the observation isn't carefully made. The sun really is white. —Preceding unsigned comment added by 207.59.146.178 (talk) 02:44, 23 April 2008 (UTC)