• merc@sh.itjust.works
    link
    fedilink
    English
    arrow-up
    1
    ·
    13 hours ago

    Still, the sun is white. Sun light is white.

    That’s why I said “appears to be yellow”.

    Are you saying the blue light is removed from the spectrum when it’s passes through the atmosphere?

    The light from the sun is made up of a whole variety of wavelengths. You can see that when there’s a rainbow and every wavelength from red to orange to yellow all the way to violet is represented. This light arrives in a continuous stream of individual photons.

    When short wavelength photons (blue wavelengths down to violet wavelengths and below) hit the atmosphere, they’re more likely to be scattered by air in the atmosphere. Because of that, they still hit the ground, but they’re no longer coming from a direct line from the sun. That’s why when you look up at the sky you see it as being blue, because photons that weren’t originally heading toward you were scattered and come towards you from a random direction.

    The longer wavelengths, from green on up aren’t as likely to be scattered by the atmosphere, so they mostly come in a direct line from the sun to your eye.

    As a result, if you look directly at the sun (which you generally shouldn’t do) it will appear to be more yellow than it actually is. Astronauts above the atmosphere see the sun as appearing fully white. But, on the surface we see it as white minus all the blue that was scattered. The result is that the sun appears to be yellow when you’re on the surface with the atmosphere scattering things.

    At sunrise and sunset there’s even more scattering. Now even larger particles are involved, and there’s more atmosphere to shine through. The blue is removed, but so is a lot of the green and yellow, leaving only the red, which is the least likely to be scattered since it has the longest wavelengths.

    So, at sunrise and sunset the sun can appear reddish. At noon it can appear yellowish. But, if you go above the atmosphere so the blue doesn’t get scattered, you’ll see that it’s actually white.