time meridian

例句：

1. 1. The sun sets at the timemeridian of 12:00 PM.
   太阳在正午12点时落下。
2. 2. The time meridian is a crucial factor in determining thedate.
   时间子午线是确定日期的关键因素。
3. 3. The ancients used the timemeridian to mark the beginning ofeach new day.
   古人使用时间子午线来标记每一天的开始。