In Walt Whitman's "When I Heard the Learn'd Astronomer," what does the astronomer's lecture represent? What does the "moist night-air" represent?

In Walt Whitman's "When I Heard the Learn'd Astronomer," the lecture is clearly some type of presentation. The narrator gives us clues by describing what else is present at the lecture. There are "proofs," "figures," "charts," and "diagrams" mentioned on lines 2 and 3. Initially this may come across as some type of classroom, however, further details indicate this is more likely a lecture presenting some new findings regarding the state of the universe. The lecturer is an astronomer, rather than a teacher, by trade, and the narrator mentions that there was "much applause," which also suggests that this is not a student-filled classroom but a special presentation. People are there to listen and applaud as some mysterious phenomena is explained through charts and graphs. This lecture, with its new findings, represents the idea that the quest for knowledge can take away from the beauty of the natural world.

Conversely, the "moist night-air" represents everything that the lecture hall is not. It is the natural world, filled with wonder and unexplained majesty. While the poem begins in the lecture-room, the narrator soon grows weary of the facts and figures, stating "[h]ow soon, unaccountable, I became tired and sick" (6). At this point the narrator leaves and wanders outside, leaving the crowds and the stuffiness of the lecture-room behind. They find themself out of doors, where they "[l]ook'd up in perfect silence at the stars."  The description of the night-air as "mystical" lends itself to the above juxtaposition. To Whitman's narrator, and to Whitman himself, the wonders become less wonderful the more they are explained. Like the universe, the "mystical moist night-air" needs no explanation; it simply needs to be.