What is the expressive effect of the image of cloud and moon in the poem?

Cloud: Wandering wanderers use floating clouds as a metaphor for wandering wanderers, such as "I want to think of you in the floating clouds, so I think of me in the sunset" (Li Bai's "Seeing Friends Off"). Moon: Life is full of regrets, homesick for the full moon, longing for the spring and autumn, longing for the fleeting time to see the flowing water, and worrying about the drizzle of the phoenix tree. Another name for the moon: Moon, Pan Yu, Sewer, Chanjuan, Ghost Palace; Jade plate, jade wheel, Yuhuan, jade hook, jade bow, jade mirror, celestial mirror, jade rabbit, Chang 'e, toad. In China's ancient poems, it is a common brushwork to use the moon to contrast feelings. Generally speaking, the moon in ancient poems is synonymous with homesickness. Li Bai's Thoughts on a Quiet Night: "The foot of the bed is bright, is there frost?" Looking up, I found that it was moonlight, sinking again, and I suddenly thought of home. " This poem shows Li Bai's homesickness. The moon in the poem is no longer a purely objective image, but an image full of poet's feelings. In the Tang Dynasty, Wang Jian wrote "Looking at Du Langzhong at Fifteen Nights": "Tonight, the moon is full, and I don't know whose house Qiu Si will fall." The poem points out the universal human feelings of this full moon night with euphemistic questions, and implicitly shows the poet's deep yearning for his hometown friends. In addition, "Moon" has the following images (1). The bright moon contains the sadness of border people. Such as: "the sand is like snow before returning to Yuefeng, and the moon outside the city is like frost"; "The bright moon in Qin Dynasty, the retreat in Han Dynasty, and the Long March people did not return" is tragic. (2) The bright moon contains emotional helplessness. For example, Xie Zhuang said, "Beauty walks in the dust, and there is a bright moon thousands of miles away." Prayer and blessing; Zhang Jiuling "The moon is in the sky, and the horizon is * * * at this time." Hope and desire. (3) The bright moon symbolizes eternity in time and space. "If the ancients were running water today, they would look at the bright moon." The plundering of life by time and the helplessness of life in front of time are all vividly demonstrated.