What does it mean that thousands of feet suspects that the Milky Way has set for nine days?

"Flying down three thousands of feet, it is suspected that the Milky Way has fallen for nine days" means a spectacular waterfall rushing down from a height, which really makes people doubt that the Milky Way fell from the sky. These two poems describe the majestic momentum of Lushan Waterfall. Now people often use these two poems to describe the spectacular scenery of waterfalls. "Flying down three thousands of feet, it is suspected that the Milky Way has set for nine days" comes from the version of Looking at Lushan Waterfall written by Li Bai, a great poet in the Tang Dynasty. The whole poem is: "The sun shines on the incense burner and produces purple smoke, looking at the waterfall in the distance." On the high cliff, it seems to be thousands of feet high, which makes people think that the Milky Way has fallen from heaven to earth. Extended data:

The first sentence is "Purple smoke from the Rizhao incense burner". "Incense burner" refers to the incense burner peak of Lushan Mountain. This peak is in the northwest of Lushan Mountain, with a sharp and round shape, like a censer. Because of the waterfall, water vapor transpiration, in the bright sunshine, as if there is an indomitable spirit incense burner, purple smoke rises in Ran Ran. A word "health" vividly describes the scene of smoke rising. This sentence set a magnificent background for the waterfall, and also rendered the atmosphere for the following direct description of the waterfall. The second sentence is "overlooking a thousand waterfalls in Sichuan". The word "overlooking the waterfall" takes care of the title "overlooking the Lushan waterfall". "Hanging thousands of rivers" means that the waterfall is like a huge white practice, hanging straight from the cliff to the river ahead. The word "hang" changed from dynamic to static, and Visha wrote about the waterfall in the distance. The first two sentences of the poem outline a panoramic view from the big picture: purple smoke fills the air at the top of the mountain, white practice hangs in the mountain, and rapids rush down the mountain, forming a magnificent picture.