Light From The Sun

The earth has often been described as having a "goldilocks" orbit around the sun. This means that our planet is at just the right distance from the sun to be at the right temperature and at the right conditions for life to thrive. People who believe in God use the multitude of factors that just happen to be where they need to be to demonstrate that all of this must have been set up by God.

I would like to add something else to this today. We may not stop to think that we would not have our planet with the right temperature for life as we know it at our distance from the sun if the sun did not happen to be a yellow-orange star, which are not that common, but that is very true.

Stars vary in color (colour) across the light spectrum from red to blue. The blue stars are the hottest, since blue light has a shorter wavelength and is thus higher in energy than red light. Some stars are white, which is actually all colours (colors) mixed together.

You might be wondering what difference this really makes to life on the earth. However, consider that about 72% of the earth is covered by water. Water has optical properties of it's own, it absorbs light according to it's wavelength from red first to blue last. This is why the oceans appear blue and water can sometimes appear green.

Much of the light that enters the water is eventually refracted back to the surface and away. Since red light is absorbed first, it does not last long enough in it's passage through the water to be refracted back out. A sunset can make the water appear red but that is only because the light is being reflected from the water's surface. The spacing of atoms in water molecules relative to the wavelengths of light is what causes it to absorb some colors (colours) more easily than others. It is blue that most easily passes through the water instead of being absorbed as heat.

Blue stars are hotter than red stars but water reverses this by absorbing the lower-energy red light first. If we have a temperature range on earth that is just right for life with a primarily yellow-orange star like the sun, suppose that instead the earth orbited around a blue star and that the earth received the same amount of energy from this star as it does from the sun. The earth would be much colder than it is now because the water would refract more light away instead of absorbing it.

Now what if the sun were a red star instead of primarily yellow-orange? If the earth received the same amount of energy, it would be considerably hotter than it is today because water readily absorbs red light and would thus gain more heat. The sun's yellow-orange light does provide a lot of heat to water and also contains a significant proportion of red light, but does not heat water as much as a primarily red star would.