NASA Astronomy Picture of the Day 11 June 2023: What is the TRUE colour of the Sun?

Today’s NASA Astronomy Picture of the Day shows the wide-colour spectrum of the Sun.

Why do we perceive our Sun’s colour as being primarily yellow? NASA explained. (Nigel Sharp (NSF), FTS, NSO, KPNO, AURA, NSF)

What Color is the Sun? The answer to this question seems obvious -- yellow. That's what we see on a daily basis, right? But you would be surprised to know, that the true colour of the Sun is not absolute Yellow or even White. Seems confusing? Don't worry, NASA has covered it all! According to the space agency, the colour that we perceive is undeniably influenced by various factors. These include the wavelength and intensity of the light being emitted, environmental conditions, the capabilities and restrictions of our eyes in capturing light, and ultimately, the functioning of our brains.

Today's Astronomy Picture of the Day is actually the colour spectrum of the Sun. However, there are some missing colours too! The spectrum shared by NASA has the complete range of observable colours emitted by the Sun when its light is passed through a prism-like device. How do scientists observe all the colours of the Sun? NASA reveals that too.

NASA explanation

This spectrum was generated at the McMath-Pierce Solar Observatory and the revelation is intriguing. While our Sun, which appears white to us, emits light spanning nearly all colours, it predominantly shines brightest in the yellow-green region, NASA explained. The dark patches observed within the spectrum occur due to the absorption of sunlight by gases available at or above the Sun's surface. However, as every gas has its own absorption colour, it becomes easier to determine the composition of the Sun.

Why do we perceive Sun's colour as Yellow?

On Earth, the atmosphere significantly influences the colour of the Sun. As sunlight passes through the atmosphere, shorter wavelength blue light is scattered more effectively compared to longer wavelength red light. Resultantly, we experience a reduction in the blue tint of the Sun. Moreover, all wavelengths of visible light passing through our atmosphere are diminished, preventing the light that reaches our eyes from overwhelming the cone receptors. This alteration enables the brain to perceive colours in the image with a slight reduction in the blue-to-yellow spectrum. That's why we perceive Sun in yellow-hue colour during sunrise or sunset.