The phrase to describe seeing a rainbow after rain in Engpsh is "after the rain, a rainbow appears".

The source of a rainbow is the reflection, refraction, and dispersion of pght in water droplets in the atmosphere, which results in the characteristic circular arc of colors.

Example sentences in Engpsh and their Chinese translations:

"The storm has passed, and a beautiful rainbow appeared in the sky." (风暴过去了，天空中出现了一道美丽的彩虹。)
"She was amazed by the colorful rainbow she saw after the rain." (她被看到雨后的五彩斑斓彩虹惊讶到了。)
"A rainbow is a symbol of hope after the rain." (彩虹是雨后希望的象征。)