Yeats is 54 when he writes this poem as he was born in 1865. The poem is set in Coole Park owned by Lady Gregory, an aristocrat who was a great supporter of Irish Writers and she often invited them to stay at her estate, especially Yeats. He refers to this place not as Coole Park but as "Coole" which shows he is familiar to the estate. The first time Yeats visited Coole Park was 19 years ago when he was 35 and what he remembers most about it each year is counting swans which creates an image of leisure as to count "nine-and-fifty swans", Yeats must have had a lot of time and his mind must have been at ease.
The poem opens with a setting describing a soft time of day - "twilight" - when the evening fades into the night. Also the "water / Mirrors a still sky" which shows how the setting is placid and very calm as everything is relaxed and still.
But Yeats also does give a sense of energy in the verse as well: "brimming water" tells us that there is gentle vitality just below the surface of the still setting. Overall the opening verse just gives the reader a very beautiful, calm and peaceful setting, building up to a contrast in the next verse.
Immediately, Yeats again gives us his sense of familiarity with Coole Park, "The nineteenth autumn", this tells us that he has been here nineteen times before, and all at the same time in the year. There is a sudden contrast from verse 1 as suddenly there is dramatic activity in the swans as they all fly up to the sky. This is both very beautiful but also violent at the same time. This dramatic activity causes a change...