日照时长随地理纬度及季节的变化关系

Analysis of the Variation of Photoperiod with Latitude and Season

摘要: 本文首先分析了地球各点的日照时长与地球自转及公转的关系，阐明日照时长随季节变化增减的基本规律。其次，通过分析地球受太阳照射的基本几何关系与地球表面的晨昏变化，推导建立了地表任意地点日照时长随日子数变化的函数关系。此函数关系能够准确描述日照时长的季节变化、地域变化及极昼和极夜现象。最后，利用时长计算公式分析讨论了我国不同纬度的代表城市在1月和7月的平均日照时长。结合北京市的实际天文资料，对比分析了所建立的时长公式的预测精度。

Abstract: An analysis is conducted of the relation of the photoperiod on the earth with its rotation and rev-olution. The seasonal change of the photoperiod is also interpreted based on the mutual relation. Furthermore, upon analyzing the geometrical sun-earth relation as well as the day and night change on the earth, a formula is established to describe the relationship of the photoperiod and the observation location for any time of the year. With this formula, the seasonal and the geographical variation of the photoperiod can be predicted, and the phenomenon of the polar day and the polar night can be well interpreted. Finally, the formula has been applied to discuss the mean photoperiod of some representative cities in China in January and July. The prediction accuracy of the formula is evaluated upon comparing the calculated value of the photoperiod to the true value of Beijing.