If The Sun Were Blue

The sun is a star that radiates light most strongly in the yellow-orange-red range. What would it be like if the sun were a hot blue star? There are many such stars that radiate more in the blue range and are considerably hotter than the sun.

The environment on earth very much depends on what type of star the sun is. My hypothesis is that, if the sun were a blue star, the earth would actually be colder than it is even though blue stars are typically hotter than the sun.

The reason for this is the way that the water in the earth's oceans handle light. Water absorbs light, but it absorbs the longer-wavelength red end of the spectrum first, and the shorter-wavelength blue last. The reason that deep water appears blue is that it is only blue light that can pass through enough distance in water to be refracted back to the surface. You may have noticed that, in photographs taken underwater, there is no red to be seen in depths below about 9 meters (30 feet), or so.

The earth's surface is about 72% water, making this a very important factor. The earth is as warm as it is because the water absorbs the sun's yellow-orange-red light before it can be refracted back to the surface. But if much more blue light was coming from the sun instead, much of this would be refracted back to space. The oceans would be a truly brilliant blue, seen both from earth and from space, but the earth would actually be colder.

With colder oceans, there would be less evaporation of water into the atmosphere. This means that there would be less weather, less rainfall, and more area of desert. The reason for the desert in southern Africa, for example, is that the ocean current offshore is cold so that there is less evaporation and thus less rainfall.

With less heating of the water near the equator, there would not be the ocean currents that we have now and which redistribute heat to higher latitudes. This would enlarge the polar ice caps and get a cooling spiral underway since ice and snow reflects much more solar radiation back to space, thus cooling the earth still further.

Land would get hot quickly during the day, but temperatures would plunge at night as in any desert. All in all, we are better off with the sun as it is no matter how brilliantly blue the water would be with a blue sun.