The "black drop effect" is an optical phenomenon that occurs during the transit of a planet across the face of the Sun, typically observed during transits of Venus or Mercury. It manifests as a distortion of the planet's silhouette, where the edges appear to be blunted or "dropped" against the Sun's bright disk. This effect makes it seem as if the planet is connected to the Sun by a dark "tail" or that it has a larger apparent size than it actually does.
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