Longfellow opens with a command to look: "Lo!" The speaker points at the western sky just after sunset, where the evening star is beginning to shine. Over the next few lines the star seems to undress and slip behind a stand of pines. Then the poem turns to the speaker's beloved, whom he addresses as "my sweet Hesperus." She too, he says, goes to her rest at night, and the light fades from her window. The central idea is a gentle parallel. The star's nightly disappearance and the beloved's falling asleep are the same quiet event, one in the sky and one in a house. Love is something the speaker reads in the heavens.
The first eight lines build that picture with unusual care. The sky is a "painted oriel," a projecting window, and "painted" suggests stained glass lit from behind. The sunset "incarnadines" its panes, a rare word that means to tint them red. The star is then compared to "a fair lady at her casement," so the architecture of the sky turns into a human scene. Notice how Longfellow delays the subject. "Shines" ends line 3, and only in line 4 do we learn what is shining: "The evening star, the star of love and rest." The sentence works like a curtain being drawn back. After that, the star "doth herself divest / Of all her radiant garments," and the pines become a "sombre screen." The star becomes a figure on a small stage, and the pines hide her, as if for privacy.
The form helps this shift of focus. This is a Petrarchan sonnet in iambic pentameter, and the octave rhymes *abba abba*. Its long rhyme words (incarnadines, shines, reclines, pines) share an *-ines* sound that lingers in the ear, much as dusk lingers. The turn comes exactly where the form invites it, at line 9, with "O my beloved." Up to that point the poem describes. After it, the poem addresses someone. The sestet rhymes *cdcdee*, and its closing couplet, "night" and "light," gives the poem a settled, final click, like a latch closing.
Sound and word choice reinforce the drowsiness. Soft *s* sounds run through the poem: "sunken sun," "sombre screen," "slumber and soft dreams." The diction is deliberately old-fashioned ("anon," "yonder," "doth," "dost"), which gives the love a courtly, timeless tone. One word is slightly surprising. The star is "oppressed" with slumber and soft dreams, and "oppressed" normally suggests weight or burden. Here it seems to mean heavy-lidded and overcome by sleep. The poem lets tenderness and tiredness blur together.
The address to Hesperus, the Greek name for the evening star, is the poem's neatest move. The speaker calls his beloved "my morning and my evening star of love." The planet Venus can be seen at both ends of the day, so the phrase suggests she is present at both ends of his. That makes the comparison a compliment as well as a pattern.
The ending sends us back to the opening. At the start the star sat at a "casement" like a lady. By the close the lady is the one with a window, and the simile has reversed itself. The last line, "And from thy darkened window fades the light," inverts normal word order so that it finishes on "light" just as the light disappears. Nothing in the text says why the window darkens, and the imagery points to rest rather than loss. A reader may still feel a faint hush at the end, the sense of a day, or a presence, going quiet.
The poem is worth studying for how economically it works. In fourteen lines Longfellow, a nineteenth-century American poet, uses a strict European form to turn a sunset into architecture, then a character, then a love poem. It shows why the sonnet's two-part shape suits comparison so well. The first half builds an image, the second half applies it, and the final couplet closes the window.