Will the real 5500K please show itself?

Before anyone picks holes in the previous post – we had huge (huge, I tell you) arguments about what colour the Sun is. Lots of really very very senior astronomers were arguing that it’s ‘obviously’ yellow, which made it rather hard for the likes of me to pursue a line of inquiry centred on the ‘but… it has to be white, by definition’ angle. Black-body radiation curves were calculated, with precise RGB mixing via colour-calibrated monitors. Counter-arguments were raised involving infinite fields of non-specular waveband-agnostic reflector – ie. ‘snow’…

There may even have been punches thrown.


  1. One of my college tutors claimed that the sun was green, and only appeared yellow because it was bright enough to saturate the blue receptors in our eyes. We would see an artificially blue-limited sun, red-shifting its appearance. And if you red-shift green you get yellow. Ta da.
    I have no idea whether this is true or not, but I tell it to people as often as possible.
    (btw: Thanks for the mention; the lightcone link points to mindhacks.com by mistake; sorry for attaching this part of the comment to the wrong post; please post a photo of the Christmas Lectures model, if you have one!)

  2. Green? Green! Pfff! It’s white, I tell you! White! White until… until it becomes a bit orangey, way off in the far future!
    It genuinely amuses me how impassioned astronomers become when the subject is broached. Roll on the days when more of us have ventured beyond the atmosphere and seen it through our own eyes. Though… does a gold filter taint the source green, or… ?
    Link fixed – good spot, thanks!
    As for a still of the RI model – I think I have one somewhere, but the plain fact is, as a flat image, on a print or on TV, it looked rubbish. In person it was stunning, but on screen – dull. Harrumph.

  3. It’s puce I tell you, the sun is puce.
    Anyone who tells you otherwise is trying to sell you something. Or commit you. I forget which…

  4. Nah, I have to tell you it’s beige. Like everything else round here…

  5. On this matter, I would advise against trusting the opinion of anybody who lives in Glasgow.
    They have ‘theories’ about the colour, of course.

  6. Well, TV’s whitepoint is based on a particular overcast sky in New York in the 60’s, if I recall correctly, which is why it is 6500K instead of 5500K. So sunlight would be yellower on TV.
    The RI lecture I remember on this was the one where they showed the film made by getting a woman who was colourblind in one eye to tell them when they had the colours matching in both. I can’t remember which one this was though (my dad used to get us tickets to them, years ago).

  7. Just to add my ha’pence worth I personally go completely with the colour of snow argument. The Sun is the definition of white.
    I developed this idea independently when I worked on the Xmas lectures with Malcolm Longair (an Astronomer) who sided with the Yellow camp.
    The Producer of those lectures never argued with Malcolm but definitely sided with white.

  8. Yes, Bryson – as I recall, the counter-argument mentioned above was indeed yours. It still rings true to me, and I still think Malcolm was dead wrong. But heigh-ho.

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