the blue welkin
under the welkin
vast welkin
A: Look up! The welkin is so clear today.
A：看上面！今天的天空如此清澈。
B: Yes, it is a beautiful day for walking.
B：是的，今天真是个散步的好日子。
1) 天空
2) 苍穹
3) 天顶
1. 天空，苍穹
noun
1. The sky or the heavens.
Synonym: sky, firmament