The title does most of the heavy lifting before the first line arrives. Perigee is the point in the moon's orbit where it swings closest to the Earth, so the poem opens with an idea of nearness. Then the first word is "alone." That contradiction drives the whole piece: a night of closest approach that is also a night of isolation, and the suggestion that being near something large and strange can feel like loneliness.
The first stanza makes its comparison and then deflates it. "Alone like the moon" sounds like the start of something grand, but the next line brings us down to earth with "I had cold meat," and the stanza ends on the oddly flat "at twelve at night." The speaker could have said midnight, which would have been more poetic. "Twelve at night" is how someone reports the time without dressing it up, and the plainness makes the scene believable. One pictures a late snack of leftovers, eaten without ceremony. Yet the moon and the meal are not unrelated. "Cold" belongs to both, and the moon's chill seems to settle on the food. The lofty and the humble sit side by side.
The second stanza introduces something stranger. "I could not sing ordinary songs / with so serious an angel / by the door." The verb matters: "could not," not "would not." The speaker is overcome, not stubborn. "Ordinary" also hints that the speaker normally does sing, perhaps to fill a quiet room, and that tonight calls for a different kind of music or none at all. The angel is a character with a mood, and "serious" is a quietly funny word for a heavenly being, as though the visitor were a stern guest who has arrived at a bad moment. The phrasing "so serious an angel" has a slightly formal, old-fashioned lilt that suits the subject. The poem never says whether the angel is real, imagined, or a name for the weight of the hour, and "by the door" makes it more uncertain still. A door is a threshold, so the angel could be arriving, leaving, or standing guard.
The sound of the poem supports this hush. There is no punctuation, no capital letters and no end rhyme, so the lines drift down the page like thoughts at night. But the vowels do quiet work. The long "o" and "oo" of "alone," "moon," "cold" and finally "door" run through the poem like a low hum. A long "i" also recurs in "like," "I," "night," "I" and "by," which keeps the speaker's own presence ringing faintly through the lines. The poem also changes vocabulary partway through. Almost everything in the first stanza is a one-syllable word, apart from "alone." The longer, weightier words ("ordinary," "serious," "angel") only arrive with the visitor, as if the language itself straightens up when the angel appears. It is a nice irony that "ordinary" is the most cumbersome word in the poem. The line lengths shift too. The second stanza stretches out and then ends on the short, three-syllable "by the door," which closes the poem softly, like a door being drawn shut.
What makes the poem worth reading is how much it holds in so few words. It is a small domestic scene (one person, one meal, one late hour) that opens onto the cosmic and the spiritual without any fuss. The poem does not explain the angel or tell us what the speaker feels, and it trusts the images to carry the mood. The title offers a final turn. A perigee is only a moment on the way around an orbit, so the closeness it promises is temporary, and the speaker's brush with something greater is brief too. Silence, in this poem, becomes the most fitting answer to that kind of presence. The speaker cannot sing, but the poem itself, short and hushed, is the song that the occasion allowed.