radius of curvature of meridian

例句：

1. 1. The sun isdirectly overhead at noon, marking themeridian of the day.
   中午太阳直射头顶，标志着一天的子午线。
2. 2. The meridian divides theearth into two hemispheres.
   子午线将地球分为两个半球。
3. 3. Themeridian line is used to determinethe longitude of a location.
   子午线用于确定一个地点的经度。