What color is the universe?

When you look at the night sky, it is easy to think that the universe is an endless sea of ​​darkness. But if you measured the visible light of all luminous celestial bodies, what would the average color of the universe be?

Let’s put that aside first: it’s not black.

“Black is not a color,” Ivan Baldry, professor at the Institute for Research in Astrophysics at John Moores University in Liverpool, UK, told Live Science. “Black is just the absence of detectable light.” Instead, the color is the result of visible light, which is created throughout the universe by stars and galaxies, he said.

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In 2002, Baldry and Karl Glazebrook, distinguished professor at the Center for Astrophysics and Supercomputing at Swinburne University of Technology in Australia, co-led a study published in The Journal of Astrophysics which measured light from tens of thousands of galaxies and combined it into a singular spectrum that represented the entire universe.

In doing so, the couple and their colleagues were able to determine the average color of the universe.

The cosmic spectrum

Stars and galaxies emit waves of electromagnetic radiation, which is separated into different groups depending on the length of the transmitted waves. From shortest to longest wavelength, groups include gamma rays, X-rays, ultraviolet lightvisible light infrared radiation, microwave and radio waves.

Visible light is a tiny part of the electromagnetic spectrum in terms of wavelength range, but it’s the only part the naked eye can see. What we perceive as colors are in fact just different wavelengths of visible light; reds and oranges have longer wavelengths, and blues and purples have shorter wavelengths.

The visible spectrum of a star or galaxy is a measure of the brightness and wavelengths of light emitted by the star or galaxy, which, in turn, can be used to determine the average color. star or galaxy, said Baldry.

In 2002, Australia’s 2dF Galaxy Redshift Survey – which was the largest galaxy survey ever taken at the time – captured the visible spectra of more than 200,000 galaxies in the observable universe. By combining the spectra of all of these galaxies, Baldry and Glazebrook’s team were able to create a visible light spectrum that accurately represented the entire universe, known as the cosmic spectrum.

The comic spectrum “represents the sum of all the energy in the universe emitted at different optical wavelengths of light,” wrote Baldry and Glazebrook in a separate, unpaired article. paper line in 2002 based on their discovery. The cosmic spectrum, in turn, allowed them to determine the average color of the universe.

Color conversion

The researchers used a color-matching computer program to convert the cosmic spectrum into a single color visible to humans, Baldry said.

Our the eyes have three types of light-sensitive cones, each of which helps us perceive a different range of visible light wavelengths. This means that we have certain blind spots where we cannot properly register certain wavelength colors between these ranges, wrote Baldry and Glazebrook in their article online. The colors we see also depend on our benchmark for white light when we observe an object. For example, the color of an object may appear different in a brightly lit room compared to outdoors on an overcast day.

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However, the CIE color spaces, created by the International Commission on Illumination in 1931, compensates for our visual limitations by assigning a color to different combinations of wavelengths seen by a standardized human observer, which the team’s computer models used.

The team determined that the average color in the universe is a beige shade not too far from white. Although this is a rather boring find, it is not surprising, given that white light is the result of the combination of all the different wavelengths of visible light and the cosmic spectrum includes such a wide range. wavelengths.

The new color was eventually named “cosmic latte”, based on the Italian word for milk, after a survey of the entire research team. Other suggestions included the cosmico cappuccino, big Bang beige and primordial clam chowder.

Move red

A key concept of the cosmic spectrum is that it represents the light of the universe “as originally intended,” Balrdy and Glazebrook wrote in their online article. This means that it represents light as it has been emitted throughout the universe, not just as it appears to us on Earth today.

Like all waves, light stretches great distances due to the Doppler effect. As light stretches, its wavelength increases and its color shifts towards the red end of the spectrum, known to astronomers as the redshift. This means that the light we see is not the same color it was when it was first emitted.

“We removed the effect of the redshift from the spectra of galaxies,” said Baldry. “So these are the spectra of galaxies when they emitted light.”

So the cosmic slat is the color you would see if you could look at the universe from above and see all the light coming from every galaxy, star, and gas cloud at once, Baldry said.

Originally posted on Live Science.