Supposedly, daylight at midday has a colour temperature of 6500 K. This reference is also the standard for calibrating computer screens (that's how I fell into this). However, outside the atmosphere the sun has a colour temperature between 5770 and 5900 K.
I've looked everywhere I could, and nowhere is this difference explained, so I'm asking here.
I understand that (together with other effects) Rayleigh scattering redirects blue light, and that as a result, the sun looks more yellow than in space, while when we look at the sky, we see the missing blue light. However, a white object would receive both the direct sunlight as well as the diffused blue light, resulting in the same sum total. If anything, I would expect more blue light to be reflected into space and thus a lower colour temperature.
I did manage to find out about Chappuis absorption, which results in a blue sky during twilight, though it was never mentioned in the context of daylight. If I look at all absorption occuring in the atmosphere, as shown in a typical solar spectrum diagram, blue light is actually absorbed more.
The only theory I could come up with myself is that light tangential to the earth could contribute, as some of its blue component is redirected to the earth while the remainder is not, but I find it hard to imagine that would have enough of an effect.
What's going on here?
