Sky and Sea

[ccyy1993]

Why is the sky and the sea blue? Can anyone tell me why?

[Skids]

Oceans and seas, and other water holes, reflect the colour of the sky. Blue sky, blue ocean. You've never seen a blue ocean under a thunderstorm. Also the depth of the body of water will change its appearance as light is reflected back up from the bottom.
The sky, on the other hand, looks blue, during a nice sunny, cloudless day, because of Rayleigh Scattering.
The shorter wavelengths of the sun's white light - blue and violet light - are absorbed and then radiated out by the gaseous and solid particles floating around in the atmosphere. The longer wavelengths - red and orange light - pass straight through and hit the Earth. What you see in the sky is all the blue being scattered around up there and then reflected back down at you. You're looking at trillions upon trillions of molecules all reflecting blue light.
Closer to the horizon the sky looks more pale because the blue light has more atmosphere to travel through to get to you, so more of it is scattered away.
Rayleigh Scattering is also why the sun looks yellow down here on Earth. In space, where there is no atmosphere to disrupt the white light, the sun looks white. Because the blue light is being scattered around the atmosphere, it is no longer in the direct rays of the sun, so you only see the longer wavelengths; reds and oranges.

[magicdice]

skids you don't explain why the sea is different colours in different places, and why sometimes it looks almost green. why are there light and dark colour bands when you look out over the ocean? is it to do with the plant and animal life there?

i was under the impression, misguided as it may be, that the sea was blue because that's what colour water is, which didn't seem that unlikely because lots of compounds

[zipadeedodah]

I knew that water was only blue because of the refelction from the sky, but didn't have a clue about why the sky is blue...thanks Skids, very interesting!

[Escher]

I'll go with Skids on the sky blue scattering explanation.

Water is blue all on its own. If you were curious enough, get a long tube (notice I can't remember how long, not the kind of thing you are bound to have lieing about), with glass ends, and fill it with the purest H2O you can find. Shine a nice bright white light in one end and stick your eye on the other. If you see any colour other than blue, call me.

I've also spent some time in ice caves, and they are very blue, and beautiful.

[rooftrouser]

I have lived by the sea nearly all my life and can tell you that in the English Channel it is very rarely blue. While both the reflection and colour of water replies are part of the answer they don't cover why it ranges in appearance from brown through grey, green and turquoise as well as tvarious shades of blue. Certainly the absorption of red and yellow light and the reflection of blue is a major factor as is the colour of the sky but so are stirred up mud from the bottom and other sediment carried in by rivers etc (often chalky in this area). Other factors affecting the perceived colour of the sea are banks of seaweed close to the surface and algae or phytoplankton and as Skids noted, light reflected off the bottom affected by depth. Unfortunately it is very far from pure H�0 in our coastal waters.

[Minimatronic]

for my own personal amusement, i strongly feel that everyone should go to

www.searchers.com/ask/

and ask diana 'why is the sky blue?'.

it's seriously baffling to have a strange 5 year old style bot informing you of raleigh scattering.