The sunset skies of burning roses and peaches are a unique benefit of our home on Earth. But what colors appear when the sun sets on other planets in the solar system?
The answer depends on the planet. On Mars, the sun comes and goes with a blue glow. On Uranus, the evening sky turns from blue to turquoise, according to NASA. And on Titan, one of Saturn’s moons, the sky changes from yellow to orange and brown when the sun goes below the horizon.
Sunset colors are not uniform because, in large part, these shades are a product of each planet’s atmosphere and how particles scatter sunlight, according to Kurt Ehler, a professor of mathematics at Truckee Community College in Reno, Nevada, and lead author of a 2014 article in the magazine Applied Optics who investigated why the Martian sunset looks blue.
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“It is complicated,” Ehler told Live Science. “Everyone had a preconceived notion that the mechanism [for sunsets] it is a replica of what we see on Earth. “But that is not the case.
On Earth, the atmosphere is made up of small gas molecules, largely nitrogen and oxygen, that are more effective in scattering, i.e. absorbing and re-emitting, in a different direction, light of short wavelengths, such as blue and violet. , which is longer red wavelengths. The selective type of scattering caused by small molecules is called Rayleigh scattering. It gives us a blue sky at noon, but at dusk and dawn, when sunlight must travel farther, more blue light is scattered; It is the longest red and yellow wavelengths that reach our line of sight, creating the vibrant shades of red that we see.
Any planet whose atmosphere is dominated by gas will follow a similar pattern of longer wavelength colors that will become more dominant at sunset, Ehler said. On Uranus, for example, hydrogen, helium, and methane gas particles in its atmosphere scatter the shorter blue and green wavelengths while absorbing (but not re-emitting) longer red wavelengths, according to NASA. This creates a bright blue sky that turns turquoise at sunset as the blue light scatters relative to the longer, greener wavelengths.
If a planet’s atmosphere is dominated by something other than gases, everything about how the sunset appears will be different. Take the Martian blue sunset. “The density of atmospheric gas is only about 1/80 of what it is here,” Ehler said of Mars. “The dispersion is dominated by larger dust particles.”
In a 2014 study using data from the Mars rover Spirit, Ehler and colleagues found that Martian dust scatters light very differently than gas molecules. “The reason for [the] blue sunset is the pattern in which light scatters [dust] particles, “he said.
Gas molecules, like those on Earth, scatter light in all directions. In contrast, dust scatters light primarily in one direction: the forward direction, Ehler said. Additionally, dust particles scatter red light at much wider angles than blue light. Because blue light is not widely scattered, it becomes more concentrated, so “blue light is about six times more intense than red light” on Mars, Ehler said.
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When you look at the Martian sunset, you actually see that “the sun’s disk is white, because the light doesn’t change color as it passes through the Martian atmosphere,” Ehler said. “Around the sun is a bluish glow. And also outside, the sky is starting to look reddish. There, you’re seeing red lights scattered at larger angles. ”
As for the other planets and moons, it is almost impossible to predict what the sunset will look like without having a deep understanding of its atmospheric composition. If these celestial bodies have a gaseous atmosphere, you would expect to start seeing longer wavelengths of light at sunset, Ehler said.
“Where [the] the atmosphere is dominated by other substances, I can’t tell you, “Ehler said. Different types and size distributions of dust will scatter light in unique ways. In other words, if you think a sunset on Earth is” out of this world, “Think again: it really is a unique characteristic unique to planets with gaseous atmospheres.
Originally published in Live Science.
