Two short stanzas, and a sudden turn from the sky to the self. In the first, the sun sinks onto the sea, and the poet compares it to "a public head." That's a strange, slightly unsettling image. A head suggests a face, something round and present, and "public" makes it feel exposed, a figure everyone can see, going down in full view of anyone watching. There's something both ordinary and a little awkward about it.
Then the poem turns inward. The speaker admits, "I cannot understand / what I have been today." It's a quiet confession. The day is ending, and instead of feeling settled or satisfied, the speaker feels unable to make sense of their own part in it. The sunset seems to invite a summing-up, and the speaker can't manage one.
The mood is hushed, reflective and a bit puzzled, with no drama. The poem leaves us with the calm of dusk and an unanswered question about who we were in the hours that just passed.