Welcome to the land of symbols, imagery, and wordplay. Before you travel any further, please know that there may be some thorny academic terminology ahead. Never fear, Shmoop is here. Check out our "How to Read a Poem" section for a glossary of terms.
We think that going to see an astronomer explain the stars and planets would be fun, but the speaker isn't having any of it. He doesn't like the way the astronomer puts the mysteries of nature into numerical form. You get the impression that the speaker (and perhaps Whitman himself) does not understand math very well, as he seems to throw out general terms without noting any relation between them: Proofs! Figures! Charts! Divide!
Line 2: If you've ever been confused in math class, you know exactly what the speaker is describing here: a flurry of numbers that don't seem to fit together. The phrase "before me" turns the numbers into a concrete image. The word "ranged" could be a pun: the primary meaning is "ordered," but the word can also mean the opposite, "wandered." It's as if the numbers were wandering away from his understanding.
Line 3: This line contains more concrete math images: "the charts and the diagrams." The word "them" does not have a clear referent, as far as we can tell. Does it refer to the figures, the proofs, the charts, all of the above? (OK, now we're starting to sound like a math quiz.)
Line 5: The word unaccountable looks like a pun to us. The literal meaning is, "unexplainable" or "for no apparent reason," but it also contains the shorter word, "un-countable."
The poem is written in the voice of a plain-speaking individual. The use of such contractions and other signs of a common, folksy accent stand in ironic contrast to the refined sensibilities of the astronomer. The irony works in kind of the same way as Reese Witherspoon's accent in Legally Blond, a movie about a California Valley Girl who goes to Harvard Law School. We should note that Whitman doesn't just adopt the plain-spoken tone in this poem – he slips in and out of it like a chameleon. But it functions slightly differently here, given the context.
Title, line 1: The two-syllable word "learned" contracts to "learn'd," implying a plainspoken speaker without a sophisticated college education. It is ironic to use this tone to talk about a very sophisticated college professor.
Lines 1-4: The repeated use of the word "when" at the beginning of the first four lines is an example of anaphora. It contributes to the impression that the speaker is telling a slightly rambling anecdote.
Lines 3, 5 and 6: The speaker talks using parallel expressions that follow the formula, "this and that," "this and that." Examples include, "the charts and the diagrams," "tired and sick," and "rising and gliding out."
Line 4: We think the repetition of "lecture" in these lines sounds especially folksy. The astronomer is clearly delivering a lecture in a lecture room: does he really need to tell us that this room is, um, a lecture-room?
Line 6, 8: "Learn'd" is not the only contraction used in this poem. "Wander'd" and "look'd" are also contractions. "Look'd" is particularly baffling because the word is one syllable anyway.
The poem develops around the contrast between two different kinds of "stars" (and, no, not the Hollywood kind). The astronomer's "stars" are abstract ideas that can be reduced to numbers and charts. They reside in a noisy, crowded lecture-room. The real stars, on the other hand, reside in the infinite night sky. They give you that swooning, dizzy feeling in the pit of your stomach. When the speaker goes outside to look at them, he feels a spiritual unity with the night.
Line 6: The word "gliding" is a hyperbole. It exaggerates the smoothness and ease of the speaker's exit from the lecture-room. Unless this room happens to be located in an ice-skating rink. We doubt it.
Line 7: The phrase "mystical moist night-air" is an example of alliteration.
Line 8: The phrase "perfect silence" is a tautology, a kind of logical repetition. "Silence," the absence of sound, is by definition already "perfect." Whitman wants to underscore this point.