Astronomy Picture of the Day
Discover the cosmos! Each day a different image or photograph of our
fascinating universe is featured, along with a brief explanation
written by a professional astronomer.
2021 February 18
Swiss Alps, Martian Sky
Image Credit & Copyright: Jens Bydal
Explanation: Taken on February 6, this snowy mountain and skyscape was
captured near Melchsee-Frutt, central Switzerland, planet Earth. The
reddish daylight and blue tinted glow around the afternoon Sun are
colors of the Martian sky, though. Of course both worlds have the same
Sun. From Mars, the Sun looks only about half as bright and 2/3 the
size compared to its appearance from Earth. Lofted from the surface of
Mars, fine dust particles suspended in the thin Martian atmosphere are
rich in the iron oxides that make the Red Planet red. They tend to
absorb blue sunlight giving a red tinge to the Martian sky, while
forward scattering still makes the light appear relatively bluish near
the smaller, fainter Martian Sun. Normally Earth's denser atmosphere
strongly scatters blue light, making the terrestrial sky blue. But on
February 6 a huge cloud of dust blown across the Mediterranean from the
Sahara desert reached the Swiss Alps, dimming the Sun and lending that
Alpine afternoon the colors of the Martian sky. By the next day, only
the snow was left covered with reddish dust.
News from Mars: NASA Perseverance Coverage
Tomorrow's picture: pixels from space
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Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
NASA Official: Phillip Newman Specific rights apply.
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A service of: ASD at NASA / GSFC
& Michigan Tech. U.
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