The Glow Opposite the Sun
On the darkest nights, a faint oval glow hangs in the sky at the point exactly opposite the Sun, as if something were shining back at us.
What was reported
Far from city lights, on a clear moonless night, careful observers can sometimes see a very faint, diffuse patch of light, wider than the full Moon, sitting at the point in the sky directly opposite the Sun. It moves through the stars over the year, always keeping its place opposite the Sun.
It was first described in 1730 by the French Jesuit astronomer Esprit Pézenas, in Marseille, and the explorer Alexander von Humboldt noticed it in the tropics in the early 1800s. It was given the German name gegenschein, 'counter-glow'. Many people who have spent their lives watching the sky have never seen it.
Explanations offered
The gegenschein is sunlight reflected back by dust spread through the solar system. Dust grains directly opposite the Sun are fully lit, like a full Moon, and reflect light most strongly straight back towards us. It's related to the zodiacal light, and today it can be seen only from very dark places.
- When
- First described in 1730
- Where
- Marseille, Provence-Alpes-Côte d'Azur, France
- Witnesses
- Esprit Pézenas, Alexander von Humboldt and dark-sky observers
- Status
- Explained
Famous cases are real, widely reported events. Each file sets out what witnesses said and the explanations that have been offered, without taking a side.
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