Duplicate Image at Moonset

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."