Every clear, moonless February and March night in the Northern Hemisphere, just after evening twilight and before morning twilight, the sky is faintly illuminated above the sunside of the horizon.* That thin lucence is called the Zodiacal light. Over the opposite side of the night horizon is another just perceptible glow rarely perceived called the Gegenschein, or counterglow. In the tropics the Zodiacal light appears every clear night, except when the moon outshines it. The light of the milky way blots out the Gegenschein during December, January, June and July. Other times it...
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