December - snowflakes You are here: Home Photo gallery Atmospheric optics Twilight phenomena Twilight wedge


The twilight wedge is the dark shadow band of the earth, visible in the east when the sun has just set, or in the west if the sun is nearly rising. During sunset, the shadow band rises quicker than the sun sinks below the horizon and gradually smoothens out with the evening sky, because the observer first sees the shadow edge-on, when the tangent point of the sunlight on the earth is near the observer (i.e. the sun is very near the horizon), and later on, the tangent point through which the edge of the shadow runs has moved westward. For sunrise, the sequence is reversed. Often, one can see a reddish to brownish haze along the border of the shadow. This is called the belt of Venus.

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