外接圆

例句：

1. 1. The outer circle of the planet is where the atmosphere begins.
   行星的外圈是大气层开始的地方。
2. 2. The outer circle of the city is lined with tall buildings.
   城市的外围是高楼大厦。
3. 3. The outer circle of the park is a popular spot for jogging and exercise.
   公园的外围是慢跑和锻炼的热门地点。