Is
the night sky darkest in the direction opposite the Sun? No. In fact, a rarely
discernable faint glow known as the gegenschein (German for "counter
glow") can be seen 180 degrees around from the Sun in an extremely dark
sky. The gegenschein is sunlight back-scattered off small interplanetary dust
particles. These dust particles are millimeter sized splinters from asteroids
and orbit in the ecliptic plane of the planets. Pictured above from last year
is one of the more spectacular pictures of the gegenschein yet taken. Here a
deep exposure of an extremely dark sky over Las Campanas Observatory in Chile
shows the gegenschein so clearly that even a surrounding glow is visible.
Notable background objects include the Andromeda galaxy, the Pleiades star
cluster, the California Nebula, the belt of Orion just below the Orion Nebula
and inside Barnard's Loop, and bright stars Rigel and Betelgeuse. The
gegenschein is distinguished from zodiacal light near the Sun by the high angle
of reflection. During the day, a phenomenon similar to the gegenschein called
the glory can be seen in reflecting air or clouds opposite the Sun from an
airplane .
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