The Blue Sky Hypothesis

One day, I realized that if there was no land on earth, if the surface was all ocean, the sky would not be blue.

It is well-established that electromagnetic radiation, such as light and radio waves, are reflected by objects that are similar in size to the wavelength of the radiation. This is why AM radio signals are interrupted as you pass under a bridge overpass, while FM signals are not. The AM signals have a longer wavelength, similar to the width of the overpass. The shorter FM signals reflect around it.

The blue color (colour) of the sky is caused by particles of dust in the air. The size of most of the particles is such that the yellow, orange and, red light from the sun has a longer wavelength and can go "around" the dust particles while the blue light of shorter wavelength, similar to the size of the particles, is reflected and scattered by them. This is why the yellow, orange and, red light of the sun comes straight to us while the blue is scattered all around the sky.

During the evening, the sunlight has to pass through a thicker section of atmosphere to get to us due to it's angle in the sky. This means that the light must pass through more dust particles before we see it. This causes the next longest wavelength, yellow, to be scattered out by the dust in the atmosphere so that the evening sun appears orange or red. From space, a blue line can be seen across the earth where dusk is at the moment caused by blue being scattered out of the atmosphere altogether.

We know that a prism, a triangular piece of glass, will break a beam of white light down into it's component colors (colours). White is a mixture of all colours (colors) and consists of red, orange, yellow, green, blue and, violet. Clouds consist of millions of water droplets condensed on dust and snow consists of millions of ice crystals. These appear white because they act as millions of tiny prisms, breaking down incoming light into it's component colors (colours) and then recombining it into white.

The blue of the sky is generally light in tone because there is plenty of white light mixed with it from water in the air. The sky in the desert tends to be a darker blue than skies elsewhere due to the lack of water. This is because there is more dust to scatter blue light around and less water to scatter white light to mix with it to produce the usual light blue sky.

I would like to speculate that the sky tends to appear a lighter blue in tone toward the horizon because of the different light scattering methods of dust in comparison with the water in the air. The water refracts light while the dust reflects light. Thus, dust in the air returns more of the light that falls on it to space than the water in the air does.

This means that when you look at the blue of the sky toward the horizon, you are looking through more of both dust and water than when you look straight above you. The increase in dust toward the horizon because of the thicker atmosphere reflects more blue light back to space than the increased amount of water in the air that you are looking through sends white light back to space. This is due to the simple difference between reflection and refraction.

I cannot see that this has ever been pointed out before. The air itself has little effect on light or we would not be able to see faint stars in space. Land is the source of dust on the earth, except for meteors. This can only mean that if there was no land on earth, if the world was all ocean, the sky would be white instead of blue. It is true that salt from the oceans also gets into the air and acts upon light in the same way as dust but it seems to me that this occurs primarily where ocean waves break against a shore.

If the earth had weaker gravity, meaning that larger dust particles could stay aloft, the sky could appear yellow, or even orange, instead of blue. If the gravity was so strong that no dust or water was in the atmosphere, the daytime sky would be black and the brighter stars would be visible in the daytime.