The whole poem of the "Rime of the Ancient Mariner" is filled with vivid imagery, and the two stanzas you refer to in your question are no exception. At the end of part 1 the mariner shoots the albatross for no good reason, and the aftermath of that act starts immediately in section 2. The wind that had been moving the boat has ceased and things are not looking hopeful for the sailors on the ship. In the 7th stanza the language of the poem describes the sun. With no breeze, the silence of the sea and the ship is eerie and the heat of the sun sounds ominous. The sky is described as 'copper.' Copper is a rich, shining golden orange color and that sounds pretty until you consider the next line which reveals the "bloody Sun, at noon." The sun is usually described as yellow, but to extend the heat and intensity to orange and red suggests a significant increase in the heat of the sun. Noon is the point of the most intense heat of the day and the sun is directly overhead which is why the mariner relates that the sun "right above the mast did stand, / No bigger than the moon." Because is straight overhead it appears smaller than in the horizon, but that does not diminish its power.
In the 8th stanza, the first line uses repetition to stress the passage of time. "Day after day, day after day" suggests more than four days and even four days with absolutely NO motion would seem impossible for the men on this boat. He explains that there was absolutely NO wind (breath) and NO motion. To make the experience more vivid he uses the metaphor of a painting. Paintings may show action or motion, but they aren't actually in motion. That is the situation of the ship. The ship is not moving any more than a ship in a painting is moving. The ship and the ocean are like flat images with no life in them. These two lines emphasis the complete lack of wind and forward movement for this ship.