why do we see the sun as yellow

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).


Answered by: 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. Answered by: David Kessel, Ph. D. , Professor, Wayne State University, Detroit Is the Sun yellow or white? IБve heard multiple sources say the sun is white, that it just looks yellow because the EarthБs atmosphere is scattering the blue light. IБve heard in other places that the sun is yellow because of its position in the Hertzsprung-Russell (H-R) Diagram. Which is it? It canБt be both yellow and white at the same time, or can it? The Sun emits a lot of energy in the visible range. In wavelength scale it is from 390 nm to 700 nm, and when you translate it to colors, you get all colors from violet to red, just as we see them in the rainbow. When you mix all those colors together you get white, and that is why white is the true color of the Sun. Check out photos of the Sun taken by astronauts (with no filters).


The Sun appears white on them! But seen from the Earth, the Sun can have many colors: from whitish-yellowish when it is high above the horizon, to red when it sets or rises. But you are right - most people see it as yellow, because the shortest wavelengths (that we see as different shades of blue) are being scattered by the EarthБs atmosphere, coloring the sky blue. And when our eyes combine all those rainbow colors, except the blue ones, the SunБs color our eyes see is yellowish. The lower toward horizon the Sun is, the more blue is scattered and the БaverageБ SunБs color shifts to red. The position of star on the H-R Diagram depends on starБs temperature and brightness. One of versions of H-R diagram is often called Бcolor-magnitude diagramБ, but here БcolorБ (or Бcolor indexБ) is a number representing a difference in stellar brightness in two chosen spectral ranges. In many H-R Diagrams stars are colored according to theirs temperatures (blue for hot stars, red for cool ones) to make them more informative and appealing. The Sun and stars with similar temperatures are yellow when observed from the Earth, and that is why they are often represented with this color and called Бyellow dwarfsБ.


However, you can also find diagrams for which real stellar colors are kept and in those diagrams Sun will be a white point. In some H-R Diagrams colors are coded with the wavelength for which star emits the most of its energy. When we use this criterion, we should use green for the Sun. But why donБt we see green stars (from Earth or space)? It is because stars emit energy in a really wide range. Even if the peak falls in green, a lot of energy is emitted in all colors, from blue to red. And with our eyes, we always observe the mixture of those colors. If you add a bit of blue to green, you will get something our eyes interpret as a tint of blue, and when you add something from the red side - you get yellow. So, when you see a colorful H-R diagram, remember that choice of colors is up to its author and the palette used does not necessarily represent the real colors of stars. Please, remember to be careful when checking SunБs color. Looking directly at the Sun, even with sunglasses, may hurt your eyes! Dr. Monika Adamow UT Austin

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