Observations were made over a great lake with a clear view to the horizon of moonsets that displayed a duplicate image below. This is known as an Etruscan Vase or an Omega effect because of the shape. Three causes of the inferior image are considered: refraction, reflection, or gravitation. "Since the phenomenon is only seen from a low vantage point looking over a level surface to a clear horizon it underscores the importance of the observer's position."
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