I have asked several, individuals this question and have yet to get an answer that satisfies my intrests. What color is sea water or water in general? I have had several people tell me it is the reflection of the sky in the water that gives it, it’s blue color. But out in deep water, under oil rigs, at night, when they have their bright lights on it still has a blueish color. I have also seen several photographs of icebergs that also have a blue color to them…any thoughts…
Zer0
water in general is colorless. However, if you pass light through enough water, the light will scatter, much as light scatters when passing through the atmosphere. Thus, both appear blue for much the same reason.
Sea water also looks green; I suppose this may be part of the scattering effect, but it’s also because of algae and dissolved minerals.
Finally, the reflection of the sky and the brightness of sunlight combine to make the surface of sea water look very blue on bright days, and practically black on dark cloudy days.
The true color of water would be based upon what wavelengths of light it absorbs in the visual spectrum. This link gives some references. If you look at one reference’s data, you see which wavelengths are absorbed more, namely, the longer red, orange, and yellow wavelengths, you can easily see that the spectrum colors left are green, blue, indigo, and violet. The green wavelengths are absorbed a little more than the others, so the color of water is a blue tinged with green.
I’ve seen green, blue, and (not suprisingly) aqua. Often with a kind of brownish tinge. I’m sure that the different amounts of minerals, sand and soil particles, and organic matter makes a big difference.
But one thing I never understood is why Homer often referred to the sea as “wine-red” or “blood-red.” I don’t think he was (always) describing the sea at sunset. Anyone know?
A red algae bloom possibly? Also called Red Tide.
You’re not the first to wonder about that, but I think the usual translation is “wine-dark,” not “wine-red.” I have no idea which is the better translation. Cecil touches on the topic of color in Homer in one of his columns, Could early man only see three colors?
And they got that wrong a lot too.
Sea water is blue due to scattering, but it’s not the same phenomenon as the scattering that makes the sky blue (and, in consequence, the sea isn’t the same blue as ythe sky – it’s much deeper and darker). Sky blue is due to mostly single-scatter following Rayleigh’s law, in which the scattering probability goes as the inverse fourth power of the wavelength. Ocean scattering is multiple-interaction scatter, and the relationship is much more complex. There are several books on this, and The American Journal of Physics published a pretty good article on the topic circa 20-30 years ago.
Sea water that is deep enough to have absorbed all the light entering it will appear black if you look straight down through it and can keep surface relections out of the picture. The water it’s self is clear; it’s the stuff floating in it and the way the light is absorbed to different degrees that gives it it’s apparent colour.