How does Walt Whitman use imagery in When I Heard the Learn'd Astronomer?

After withholding any imagery of nature from the first quatrain in the lecture room, Whitman saves a vision of space for the very last word of the poem, setting the image of the stars alone by preceding them with "perfect silence" and following them by the end of the text. While the scientists are left applauding themselves in the lecture room, the speaker and the reader are left with this striking impression of endless, spiritual space.