Phil Plait's Bad Astronomy: Misconceptions says “The Sun, for example, should peak at about 5000 Angstroms or so, having a surface temperature of 5500 K. However, due to complicated processes, it actually peaks bluer than that, around 4800 Angstroms.”
Various other sources give different answers for the sun’s surface temperature, but they’re all within the range 5500-5820K. By Wien’s Law (T = 2.9e-3/lambda), it would have to be 6042K to be 480nm.
So, what are those “complicated processes” that Bad Astronomer Phil Plait mentioned offhand and Wikipedia ignored?
The maximum wavelength output from the surface of the sun (originating from the photosphere) is approximately 500 nanometers (varying from exact measurements of 483 to 520 nm, depending on the temperature used to represent the surface of the sun, which is not clearly defined), while wavelength output from the inner zones are as short as (or even shorter than) 2.9 × 10-10 m (0.29 nm, which is located in the gamma ray portion of the electromagnetic spectrum). The max wavelength outputs vary along this wide range because the peak wavelength relies directly on the temperature of the blackbody, where higher temperatures lead to shorter peak wavelengths.
So basically, it sounds like the answer is that the sun radiates from more than just its outer surface, and even the surface doesn’t have a clearly defined temperature anyway, so you can’t just treat it as a solid blackbody.
As for Wikipedia, looking at the page history and discussion, they’ve been through three graphs–a 5523K curve, a 5800K curve, and a 6000K-ish curve whose file comments say it’s a 5525K curve.
The discussion page is confusing, but it sounds like the sun is only close to a blackbody out to the 5800K surface right below the chromosphere, and beyond that various corona effects screw up different parts of the spectrum differently. Apparently the overall curve best fits a 5523K surface, but there are parts that match that very badly.
I still have no idea where the 480nm (6042K) peak comes from, but I can see that there’s not likely to be an answer here that I’ll understand. I should have just left it at “complicated processes” once I found that Bad Astronomy page.
For a rough analogy, what is the absolutely accurate temperature of a kitchen oven?
Well, it’s tough to answer that, too. If it’s set to 350ºF, that is a reasonable average for the oven. But if you took detailed temp readings at various places in the oven, they would differ. The top is probably hotter, since heat rises. The bottom is also likely hotter than the middle, since the heat elements are down there. And the corners are likely to be cooler (my mother had specific ways to put cookies on the tray, otherwise the ones in the corner wouldn’t get baked completely).
So even with a much simpler kitchen oven, it’s complicated to get a really accurate answer.
