Space expert shows off inflatable lunar habitat
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For us terrestrial-based humans, the appears to be yellow, occasionally turning into a red-orange hue at specific times of the day. However, in reality, the Sun emits an entire spectrum of light, consisting of every single colour of the rainbow. The reason we observe our nearby Star as yellow is primarily due to a light refracting phenomenon.
One piece of evidence for this phenomenon is that while the Sun appears yellow on Earth, as we leave the atmosphere, it appears white.
Responding to a tweet talking about the phenomenon, NASA astronaut Scott Kelly tweeted: “I can confirm this space fact.”
According to NASA, when sunlight, which consists of a full spectrum of light, passes through the atmosphere, the blue light, which has a shorter wavelength is scattered more efficiently than red light.
This is why humans don’t perceive blue light when it passes through the atmosphere.
Meanwhile, all wavelengths of visible light passing through our atmosphere are diminished so that the light that reaches our eyes does not immediately saturate the cone receptors.
NASA wrote: “This allows the brain to perceive colour from the image with a little less blue – yellow. Though it does not affect what our eyes see, all x-ray and gamma-ray radiation is filtered out before it comes close to the ground.
“Most UV is absorbed by stratospheric ozone (above 10km) and most IR is absorbed by water vapour and other molecules with non-zero dipole moments.”
This effect also explains why sunrises and sunsets appear red, during this time, light travels further, due to which even more blue light is scattered and a much greater percentage of the longest wavelength (red) light makes it to our eyes.
NASA also noted that even though sunlight consists of every colour on the spectrum, in space, the light entering our eyes is so powerful that the three colour cone cell receptors, measuring red, green and blue, are completely saturated, hence appearing white.
What we perceive as colour, actually depends on the frequency of the light, with Christopher Baird, an assistant professor of physics at West Texas A&M University noting: “The entire sun and all of its layers are glowing.”
Speaking to Live Science, he said: “The ‘colour of the sun’ is the spectrum of colours present in sunlight, which arises from a complex interplay of all parts of the sun.
“The colour content of a beam of light can easily be identified by running the beam through a prism. These simple, cheap, handheld objects spread out the beam of light into its various pure colour components.”
He noted that “each pure colour has a distinct wave frequency” with red having the lowest frequency and violet with the highest frequency of visible light.
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When we direct solar rays through a prism, we see all the colours of the rainbow come out the other end, which is also all the colours visible to the human eye, further proving that the Sun is white.
Prof Baird continued: “The color components of sunlight are so close enough to being present in equal amounts that it is much more correct to say that the sun is white than to say it is yellow, orange, or any other single, pure colour.”
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