Credit & Copyright: Dario Giannobile
Explanation:
How does the sky turn dark at night?
In stages, and with different characteristic colors rising from the horizon.
The featured image shows, left to right, increasingly late
twilight
times after sunset in 20 different vertical bands.
The picture was taken last month in
Syracuse,
Sicily,
Italy,
in the direction
opposite the Sun.
On the far left is the pre-sunset upper sky.
Toward the right, prominent bands include the
Belt of Venus,
the Blue Band, the
Horizon
Band, and the Red Band.
As the dark shadow of the Earth rises, the colors in these bands are
caused
by direct sunlight reflecting from air and
aerosols in the
Earth's atmosphere,
multiple reflections sometimes involving a
reddened sunset, and
refraction.
In practice, these bands can be diffuse and hard to discern,
and their colors can depend on
colors near the setting Sun.
Finally, the Sun
completely sets and the sky becomes dark.
Don't despair -- the whole thing will happen in reverse when the
Sun rises again in the morning.
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NASA Web Site Statements, Warnings, and Disclaimers
NASA Official: Jay Norris. Specific rights apply.
A service of: LHEA at NASA / GSFC
& Michigan Tech. U.
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