Final answer:
The contrasting imagery in lines 9-16 accentuates the theme of alienation by juxtaposing the lively day against the isolated, quiet night, and the company of friends against solitude.
Step-by-step explanation:
In lines 9-16, the purpose of contrasting night with day and being with friends with being alone serves to emphasize the theme of alienation and the stark difference between the vibrancy of life during the day and the isolation and stillness of the night. This contrast is used to highlight these shifts in settings and moods, portraying how characters connect to their environments - engaged and anticipating during the day, but alienated and disconnected at night. The 'Early Sunday Morning' passage evokes a sense of an awakening world, full of potential and the daily hustle, while 'Nighthawks' creates an ambiance of a world 'shut down', void of human connection and the passage of time. These juxtapositions serve to focus the reader's attention on the characters' states of alienation from each other and from their surroundings, suggesting a deeper sense of disconnection from the 'civilization' and life's typical activities and relationships.