If the Sun is supposed to be producing white light, why does the sun appear yellow to the eye instead of white?
We need to start with the fact that white light
is a combination of all colors produced equally
by a glowing object. A glowing object that appears
blue is blue because it's producing more blue light than it is producing red, orange, yellow, green light.
The color of a glowing object depends on the temperature of the object. Now we can proceed to your question. Two Reasons why the Sun appears yellow:
1. The Sun's surface temperature (5,500 degrees
C) produces a range of visible light (red to blue) in which yellow is the most plentiful, but not much more than other colors it produces. If the Sun were cooler, say 2,500 degrees C, it would look red, like the stars Antares and Betelgeuse. Or if the Sun were hotter, say 15,000 degrees C, it would look blue, like the star Rigel.
2 The Earth's atmosphere acts as a kind of light
filter. Some colors are filtered more than others. The Sun is a yellow star, but the Earth's atmosphere makes the Sun look more yellow than it appears than if you were to observe it from space where it would appear more white than yellow. But you don't have to leave Earth to see that the Sun is really less yellow than it appears. If you are in the Rocky Mountains at 11,000 ft elevation, the Sun looks less yellow and more white than it does at sea level. There are fewer air molecules at this elevation to filter the Sun's other colors. Imagine what the Sun would look like from an airplane at 40,000 ft altitude--quite white! Also, when you are able to look at the Sun where you live, it's morning or late afternoon. It's easier to look at the Sun for a few seconds than it is a noon. The Sun appears more yellow at those times than it would if you were to observe it at noon (12 PM) when Sun is highest in the sky for the day; it's at its brightest and whitest--hard to look at. Because of the Sun's high position at noon, the sunlight has less air to travel through. Less air means less filtering of other colors. Remember: Light appears white because all colors are equally reaching your eyes. So, at noon the Sun appears to be more white, less yellow--closer to the way it really is! (Don't try to make this observation without hi-tech eye protection).
J Taras, M.S., Earth Science teacher, Slate Hill, NY
The short wavelengths (blue) of light from the sun are scattered by the atmosphere (which is why the sky appears to be blue.), leaving behind the longer (yellow-red) wavelengths.. From a high-flying airplane, or from the moon, the sun appears to be white.
David Kessel, Ph.D., Professor, Wayne State University, Detroit
'The strength and weakness of physicists is that we believe in what we can measure. And if we can't measure it, then we say it probably doesn't exist. And that closes us off to an enormous amount of phenomena that we may not be able to measure because they only happened once. For example, the Big Bang. ... That's one reason why they scoffed at higher dimensions for so many years. Now we realize that there's no alternative... '