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A siesta ((:ˈsjesta)) is a short nap taken in the early afternoon, often after the midday meal. Such a period of sleep is a common tradition in some countries, particularly those where the weather is warm. The siesta is historically common throughout the Mediterranean and Southern Europe. It is the traditional daytime sleep of Spain and, through Spanish influence, the Philippines, and many Hispanic American countries. The word ''siesta'' of the Spanish language derives originally from the Latin word ''hora sexta '' "sixth hour" (counting from dawn, hence "midday rest"). Siesta is also common in Italy (there called ''riposo'', ''pisolino''), where museums, churches and shops close during midday so that proprietors can go home for a long lunch and perhaps a snooze during the day’s hottest hours. Einhard's ''Life of Charlemagne'' recounts the emperor's summertime siesta: "In summer, after his midday meal, he would eat some fruit and take another drink; then he would remove his shoes and undress completely, just as he did at night, and rest for two or three hours."〔Einhard, ''Life of Charlemagne'', §24.〕 The main factors explaining the geographical distribution of the modern siesta are high temperatures and heavy intake of food at the midday meal. Combined, these two factors contribute to the feeling of post-lunch drowsiness. In many countries that observe the siesta, the heat can be unbearable in the early afternoon, making a midday break at home ideal. However, siesta is also practiced in some colder regions, such as Patagonia. This could indicate that the siesta has a stronger relation with culture than with climate. ==Biological need for naps== The timing of sleep in humans depends upon a balance between homeostatic sleep propensity, the need for sleep as a function of the amount of time elapsed since the last adequate sleep episode, and circadian rhythms which determine the ideal timing of a correctly structured and restorative sleep episode. The homeostatic pressure to sleep starts growing upon awakening. The circadian signal for wakefulness starts building in the (late) afternoon. As Harvard professor of sleep medicine Charles A. Czeisler notes, "The circadian system is set up in a beautiful way to override the homeostatic drive for sleep." Thus, in many people, there is a dip when the drive for sleep has been building for hours and the drive for wakefulness has not yet started. This is, again quoting Czeisler, "a great time for a nap."〔 The drive for wakefulness intensifies through the evening, making it difficult to get to sleep 2–3 hours before one's usual bedtime when the ''wake maintenance zone'' ends. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「siesta」の詳細全文を読む スポンサード リンク
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