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180° — straight angle and half turn
180 degrees is a straight angle, a straight line. The sum of angles of any triangle equals 180°. 'To do a 180' in colloquial language means to completely reverse one's position or direction.
Science
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180 — maximum throw in darts
180 points is the maximum possible score in a single darts turn: three darts in the triple 20. Called 'maximum' or 'one-eight-zero'. Achieving this at a professional tournament is accompanied by a special ritual.
Culture
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180th meridian — International Date Line
The 180th meridian is the opposite of the Greenwich Prime Meridian. The International Date Line runs near it. Crossing it west to east you 'lose' a day, and east to west you 'gain' one.
Dates