What is the sight referred to here?

In William Wordsworth's "Composed upon Westminster Bridge, September 3, 1802," the speaker describes watching the sunrise over the city of London and the river Thames. From the title of the poem, the reader knows that the speaker observed this sunrise from the vantage point of Westminster Bridge, which stretches over the Thames and connects Westminster and Lambeth. Rather than describing the rising sun itself, the speaker of the poem focuses on the effects of the slowly building, golden light over the city itself, listing "ships, towers, domes, theatres, and temples" as all being touched by the sunlight.
The reader can identify that this is a sunrise, rather than a sunset or simply a particularly lovely, sunny mid-morning, by a few key word choices. First, there are the lines "This City now doth, like a garment, wear / The beauty of the morning," which make it clear that this is, in fact, morning. Then, the lines "Never did sun more beautifully steep / In his first splendour, valley, rock, or hill" are important for the use of that word "first." The sun's "first splendour" implies sunrise. Finally, in the final lines, the speaker of the poem describes the houses of the city as "asleep," making it clear that this is very early in the morning indeed.