球面日晷的设计原理

Design Principle of Spherical Sundial

通过各天球坐标的关系以及日晷的投影原理设计出球面日晷,它是赤道式日晷、圭表和现代精密天文测算相结合的产物.日晷测得的时刻为当地真太阳时,根据经度差与时刻差的关系,可在晷面上直接将时刻修正为北京视时,进行均时差校正后得到北京时间.同时通过对太阳周年回归运动的分析,设置节气线,由晷针针尖在晷面投影的节气位置来判断当天所处的日期.

A spherical sundial is designed by application of the relations between different celestial coordinates and the projection principle of the sundial, which is the product of a successful combination of equatorial sundial, gnomon and modern precision astronomical measurement. Since the time measured with sundial is the local apparent solar time, the Beijing local apparent time can be easily worked out by adjusting directly the time on the dial face according to the relation between the longitude and time differences, and after a mean move-out correction, the Beijing time can thus be determined. At the same time, through the analysis of the yearly recurrent motion of the sun, the solar term lines are set and the exact date of the day can be decided by observing the sundial needle tip＇ s projection location on the surface of the sundial against the solar term lines.