......."When I Heard the Learn'd Astronomer" is a lyric poem with a single stanza of eight lines. 

Composition and Publication

.......Walt Whitman wrote the poem in 1865. The version of the poem on this page is from the 1881-1882 edition of Leaves of Grass. Click here to access all the editions of Leaves of Grass published before his death.

Main Theme

.......Mere numbers, charts, and diagrams cannot sum up the mystery, power, and beauty of the universe. To begin to understand the wonder of the universe, one must view it through the lens of the unaided eye rather than the lens of the calibrated telescope in order see a glimmer of its meaning. Other ways of stating this theme are the following:

• A romantic—that is, poetic or imaginative—perspective can yield a deeper appreciation of a subject than a scientific perspective can. 
• Cold, hard facts can obscure deep meanings of an observed phenomenon. 
• Scientific calculation can quantify and measure the components and makeup of beautiful objects but cannot fathom their allure; only romantic musing can do that. 
• Astronomy can analyze the electromagnetic radiation of a moonbeam; poetry can analyze the dreamy effect of a moonbeam on the human heart.
• Science is invaluable as a tool to help us understand the complexities of the universe. But we must guard against allowing it to indurate us to the wondrous beauty of nature.

.......A person must sometimes separate himself from the crowd to experience life and the cosmos from a different perspective. He must become an individual, a nonconformist, willing to abandon the herd to roam freely in open pastures. In the last three lines of the poem, the speaker does so. When he wanders alone in the mystical moist night-air, he looks up but does not see the wonders of celestial mechanics, astrophysics, or uranometry; he sees stars. 

Structure

.......Lines 1 to 4  consist of four subordinate clauses that establish the situation in which the speaker (narrator) finds himself. Lines 4 to 8 consist of a main clause followed by a subordinate clause with a compound verb (wander'd, look'd). Lines 4 to 8 present the speaker's response to the situation presented in Lines 1 to 4. The first of the four subordinate "when" clauses in the first half is relatively short. The second is longer than the first, the third longer than the second, and the fourth longer than the third—perhaps to reflect the growing complexity of the astronomer's explanation, which makes the speaker "tired and sick." Lines 4 to 8, on the other hand, are short by comparison—the last line being the shortest in this section of the poem—perhaps to reflect the simplicity of the speaker's approach to appreciating and understanding the stars.

Format: Free Verse

.......Whitman wrote the poem in free verse—also called vers libre, a French term. Free verse generally has no metrical pattern or end rhyme. However, it may contain patterns of another kind, such as repetition. 

Repetition of Words

For example, the first four lines of "When I Heard the Learn'd Astronomer" all begin with the same word, constituting a figure of speech known as anaphora. 

Repetition of Parallel Structure

In addition, the poem builds a syntactical pattern, parallel structure, in the following groups of words:

the proofs, the figures (line 2)
the charts and diagrams (line 3)
add, divide, and measure (line 3)
tired and sick (line 5)
rising and gliding (line 6)

Finally, the poem repeats similar sounds: heard, learn'd, heard; lectured, lecture, perfect; room, soon; rising, gliding, time, time, silence. Notice, too, the alliterations in the last two lines: mystical moist and silent . . . stars.
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Text

When I heard the learn'd¹ astronomer,
When the proofs, the figures, were ranged in columns before me,
When I was shown the charts, the diagrams, to add, divide, and measure them,
When I sitting heard the astronomer where he lectured with much applause in the lecture room,
How soon unaccountable I became tired and sick,
Till rising and gliding out I wander'd off by myself,
In the mystical moist² night-air, and from time to time,
Look'd³ up in perfect⁴ silence⁵ at the stars.

Notes

1....learn'd: This word may carry a hint of sarcasm.
2....mystical moist: This phrase may be intended to contrast with the coldly factual dryness of the lecture.
3....Look'd: Like learn'd in the first line and wander'd in sixth line, this word has an apostrophe in place of the e. Whitman does not use an apostrophe, however, in place of the e in ranged (line 2) and lectured (line 4). 
4....perfect: One may fairly ask whether this modifier helps the poem. After all, silence is silence. There is no perfect or imperfect silence; there is only silence, the absence of sound. However, speakers and writers of English often use perfect in this way—sometimes for euphony, sometimes for emphasis.
5....silence: As the adage suggests, silence speaks louder than words (of the lecturer). 

.......Following are examples of figures of speech in the poem. (For definitions of figures of speech, click here.)

Alliteration

the diagrams, to add, divide
How soon unaccountable I became tired and sick
mystical moist
silence at the stars

When I heard the learn'd astronomer,
When the proofs, the figures, were ranged in columns before me,
When I was shown the charts, the diagrams, to add, divide, and measure them,
When I sitting heard the astronomer where he lectured with much applause in the lecture room

rising and gliding

1....Write a poem in free verse on a subject of your choice. 
2....Which discipline better presents and captures the mystery and awe of the universe: science or poetry. 
3....What was Walt Whitman's attitude toward science? 
4....Write an essay that elaborates on the secondary theme.
5....Why does the speaker use gliding instead of walking in line 6? For example, is it a poetic word intended to contrast with the coldly objective words of science?

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