圆形突出部

例句：

1. 1. The moon is an annular object that appears full in the sky.
   月亮是一个环形天体，在天空中看起来是满月。
2. 2. The planet Mercury has an annular shape with a diameter of about 5,870 kilometers.
   水星有一个环形形状，直径大约为5,870公里。
3. 3. The rings of Saturn are annular and have a diameter of about 60,000 kilometers.
   土星的环是环形的，直径约为60,000公里。