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RT @JohnBarentine: Gegenschein is among the best indicators of a very dark night sky (surface brightness ~ 900 Rayleighs or near 22.0 magni…
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Gegenschein is among the best indicators of a very dark night sky (surface brightness ~ 900 Rayleighs or near 22.0 magnitudes per square arcsecond; see https://t.co/l4E6Njw5dR). Also one the faintest such phenomena in the night sky with a large angular siz