What if the sun was another color?

Q: Can the sun turn a different color?

The Sun doesnt actually change color. It is the position of the Sun relative to where you are that results in all those cool and pretty apparent changes in the color of our Sun.

Barring, of course, all other issues that wold naturally arise from the following question - if we made the sun a cooler, red star or a hotter, blue star, what impact would that have on the colour of the sky? And what colour would the sun, itself have?

Table of Contents Show

What is the colour of the Sun?
What would happen if the sun's color changed?
Why is the Sun’s colour different during sunrise and Sunset?
Is the Sun the same color every day?
What would happen if the sun was green?
Can the sun turn a different color?

I have an understanding of the concept of how the sky is coloured as it is: Blue light is what scatters the most in the atmosphere, which is why the sky is blue (and why the sunset is red; the light travels through more atmosphere so the blue scatters away entirely, yes?), and why the sun is yellowish viewed from Earth, rather than white (as that's the colour that remains when the blue scatters away). There's also some trickery with how our eyes perceive light (why it is blue, not violet).

Now, if the sun was a red star, there would be little/no blue light to scatter. Would the sky then appear red instead? And would it be as solida colour as our current sky - if red scatters less then would that mean we "saw" the atmosphere less i.e. you could potentially see stars more clearly during the day since there was less light in the atmosphere?

Similarly, if the sun was a hotter, blue star - would the colour of the sky simply be a more intense? Would the extra blue light cause us to see it as more violet, sicne we got more a stimulation from that? And would the sun itself appear blue, or white, or would it still be yellow?

I realize I'm discussing this topic a bit moreso than asking, so let me condense the central question: What colour would the sky have and what colour would the sun have in the sky, if the sun was either a red star or a blue star? (For clarity, assume that the Earth is moved so that the intensity of the received sunlight remains roughly the same)

Try this before you read further: How could you determine what color the Sun is as seen from Earth?	Image courtesy NASA/SDO
Image courtesy NASA	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. This is easy to see in pictures taken from space.
Rainbows are light from the Sun, separated into its colors. Each color in the rainbow (red, orange, yellow, green, blue, violet) has a different wavelength. Red is the longest, blue the shortest.	Image courtesy NASA/Regenbogen
Image courtesy Frank Cordova	Image copyrightVasilij Rumyantsev. Used with permission.
When we see the Sun at sunrise or sunset, when it is low in the sky, it may appear yellow, orange, or red. But that is only because its short-wavelength colors (green, blue, violet) are scattered out by the Earth's atmosphere, much like small waves are dispersed by big rocks along the shore. Hence only the reds, yellows, and oranges get through the thick atmosphere to our eyes.
When the Sun is high in the sky, the shorter waves, primarily the blue, strike air molecues in the upper atmosphere and bounce around and scatter. Hence explaining why the sky looks blue. Some people think that enough blue light is scattered out in the Earth's atmosphere to cause the Sun to appear slightly yellow. What do you think?

Some think that the Sun's output in visible light peaks in the yellow. However, the Sun's visible output peaks in the green:
	Image from Art Neuendorffer

So why are the solar images sometimes green, or blue, or red, or orange? View current images of the Sun

Actually, all forms of light and energy are part of the same phenomena: the electromagnetic spectrum. Our eyes can detect only a small amount of this energy, that portion we call "visible light." Radio waves, X-rays, microwaves, gamma rays, and the rest all have longer or shorter wavelengths than visible light, but otherwise are the same phenomena.

Scientific instruments can sometimes detect light that our eyes cannot. When people want to look at those, say, X-ray or ultraviolet images, they need to color them something that our eyes can detect. So the scientists pick some bright color, a color that would never be confused with viewing the Sun in white light. That way, we know from seeing a picture of a neon green or bright red Sun that the image was actually taken in some non-seeable version of light such as extreme ultraviolet or X-rays.

It is hard for many people, even scientists, to admit that the Sun they are so used to living with is actually white. So sometimes they even color pictures of the Sun taken in visible or "white" light to look more like something we would expect. Below is a picture of the Sun taken in visible white light, but which the scientists have processed to make it appear orange, for our benefit!

Image courtesy ESA/NASA/SOHO

Sometimes the display color of the Sun is culturally determined. If a kindergartener in the USA colors a picture of the Sun, they will usually make it yellow. However, a kindergartener in Japan would normally color it red!

In spite of these "artistic licenses", the Sun really is white!

What is the colour of the Sun?

This means the actual colour of the Sun is white. So, why does it generally look yellow? This is because the Earth’s atmosphere scatters blue light more efficiently than red light. This slight deficit in blue light means the eye perceives the colour of the Sun as yellow.

What would happen if the sun's color changed?

The color of a star is dependent upon its temperature. If the sun was a different color then it would be either hotter or colder. Either one would be bad. A pretty small difference in the output of the sun would have big effects on our planet, and a change big enough to change its color is not small.

Why is the Sun’s colour different during sunrise and Sunset?

This slight deficit in blue light means the eye perceives the colour of the Sun as yellow. The more atmosphere the Sun’s light passes through, the more blue light is scattered. Hence, during sunrises and sunsets there is a much greater percentage of red light in the Sun’s spectrum, giving often spectacular results.

Is the Sun the same color every day?

But the Sun’s color per se is imperceivably different in the scale of days or even human lifetimes, for all practical purposes the same since humans started walking on Earth. What color would the Earth's sky be if the Sun was blue?

What would happen if the sun was green?

The sun emits all colors of the rainbow more or less evenly and in physics, we call this combination "white". That is why we can see so many different colors in the natural world under the illumination of sunlight. If sunlight were purely green, then everything outside would look green or dark.

Can the sun turn a different color?

The Sun doesn't actually change color. It is the position of the Sun relative to where you are that results in all those cool and pretty apparent changes in the color of our Sun.