SDO image of the Sun in various artifical colors
How Could You Determine the Color of the Sun from Earth?


What color do you think the Sun is?

It is a common misconception that the Sun is yellow, or orange or even red. However, the Sun is essentially all colors mixed together, which appear to our eyes as white. Seen from space, this is clear:

photo of Sun from ISS, showing it is white

When we see the Sun at sunrise or sunset, it may appear yellow, orange, or red. But that is only because its shorter-wavelength light colors (green, blue, purple) are scattered out by the Earth's atmosphere, much like small waves are dispersed by big rocks along the shore. Only the long wavelengths of light from the Sun (like red, orange, and yellow) are allowed through the Earth's dense atmosphere at sunrise or sunset.

Some people claim that enough blue light is scattered out in the Earth's atmosphere to cause the Sun to usually appear slightly yellow in Earth's sky. What do you think?

How could one determine the color of the Sun in Earth's sky? Try these experiments:

  1. Glance up at the Sun in the middle of the day when it's slightly cloudy. Don't stare, of course -- your eyes can be severaly damaged by staring at the Sun!. But it's ok to glance up when you can easily see the Sun through whispy clouds. What color does it appear?

  2. What color is the Moon when it's high in the sky? Where does the Moon's light come from? (Don't be fooled by the golden glow of a rising or setting Moon. It's shortwavelenth colors are being scattered out by the Earth's atmosphere, just as they are for a rising or setting Sun.)

  3. What color are the clouds during the day (not at sunrise or sunset)? What lights up the clouds?

  4. What color is the Sun's corona during an eclipse?

  5. Find some photographs which include the Sun during the day. What color does it appear? (Though note that the response of a film or eletronic camera may not always be the same as the human eye.)

  6. Look at sunlight reflecting off the walls of a white building, or even a piece of white paper you hold up. Does the building, or the paper, look yellower in direct sunlight, or stay white?

  7. Project an image of the Sun through a pinhole camera. What color is the image?

  8. Look at some pictures of the analemma, which shows the Sun at various heights during a year. Some analemmas are taken at latitudes where the lower portions of the Sun are close to the horizon, like the one below. Can you see a difference in color? (Though, again, note that cameras do not accurately reflect colors as seen by the human eye.)
    an analemma
    Image (c) Vasilij Rumyantsev; used with permission

Can you think of other ways to determine what color the Sun is in Earth's sky?