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== Duration and geography ==
Nights are shorter than days on average due to two factors. One, the sun is not a point, but has an apparent size of about 32 minutes of arc. Two, the atmosphere refracts sunlight so that some of it reaches the ground when the sun is below the horizon by about 34 minutes of arc. The
The closer a location is to the [[North Pole|North]] or [[South Pole]], the larger the range of variation in the night's length. Although equinoxes occur with a day and night close to equal length, before and after an equinox the ratio of night to day changes more rapidly in locations near the poles than in locations between the [[Tropic of Cancer]] and the [[Tropic of Capricorn]]. In the [[Northern Hemisphere]], [[Denmark]] has shorter nights in June than [[India]] has. In the [[Southern Hemisphere]], [[Antarctica]] has longer nights in June than [[Chile]] has. The Northern and Southern Hemispheres of the world experience the same patterns of night length at the same [[latitude]]s, but the cycles are 6 months apart so that one hemisphere experiences long nights (winter) while the other is experiencing short nights (summer).
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