What colour is the Sun really?

Ask a child to draw the Sun and you will get a cheerful yellow circle, possibly wearing sunglasses. Ask most adults what colour the Sun is and they will say the same. But astronauts who have seen it from orbit describe something different. Outside our atmosphere, the Sun is white.

The short answer

The Sun is white. It gives off light across the whole visible rainbow, from violet to red, and when all those colours arrive together our eyes read the mix as white. According to the Stanford Solar Center, the Sun’s visible output actually peaks in the green part of the spectrum, not the yellow, but because every other colour is in the mix too, we do not see it as green. We see white.

The real story

The trick is in our air. Sunlight has to pass through Earth’s atmosphere before it reaches our eyes, and the gas molecules in air are much better at scattering short wavelengths of light, such as blue and violet, than long ones, such as red and orange. That scattered blue light bounces around the sky, which is exactly why the sky looks blue.

Take a bit of blue out of white light and what is left looks slightly warmer, nudging the Sun towards a yellowish tint from the ground. The effect gets much stronger near sunrise and sunset. At those times the light has to travel through far more atmosphere to reach you, so even more of the shorter wavelengths are scattered away, leaving mostly the reds, oranges and yellows. That is what gives us glowing orange sunsets.

The Space Centre in New Zealand notes that, high in the sky, the Sun appears quite white even from the ground, and that astronauts consistently call it white. A photo of the Sun taken from the International Space Station shows a bright white disc.

Of course, nobody should ever look directly at the Sun to check, which is part of why the myth survives. Most of us only see it properly when it is low and reddish, or through photos.

Why people get it wrong

Part of it is everyday experience: the moments when we can comfortably notice the Sun are usually around sunrise and sunset, when it really does look yellow or orange. Part of it is culture: the Sun has been painted yellow in picture books, flags and emoji for generations.

Space agencies add to the confusion too. Many dramatic solar images are taken in ultraviolet or X-ray light, which our eyes cannot see, so scientists give them false colours to make features stand out, often fiery orange or gold. Even special solar filters used for safe viewing can tint the Sun orange. All of that reinforces the idea of a golden Sun, when the honest colour is plain, brilliant white.

“Spent my whole life colouring it in yellow on the back of exercise books. Nobody tells a shoe sole these things, mate.”