Four short lines, no punctuation, and a title that is only three asterisks: Shel Raphen's poem gives almost nothing away at the start, and that restraint is the point. It describes a tiny event. Sunlight crosses a room, meets water hanging in the air of a shower, and becomes a rainbow. The central idea is that wonder does not need a big stage. A shower can hold what we usually look for in the sky, if someone is paying attention.
The grammar is the most interesting thing about the poem. It opens with "Sun beams", and for a moment a reader may take that as a noun, as in sunbeams, before "through the window" turns "beams" into a verb. The word also carries a second meaning. To beam is to shine, but it is also to smile, so the sun seems faintly pleased with itself. That is the only verb in the poem. Everything after it is a chain of prepositions: *through* the window, *on* droplets, *in* air, *in* my shower. The sentence travels the way the light does, from sun to glass to water to the speaker's own space. Only then does the noun it has been heading toward arrive, "A rainbow", alone on its line with no verb to explain it. The poet holds back the main word until the end, so the reader gets the same small jolt of discovery that someone standing in the shower would.
The rhythm supports this. By my count the lines run to six, eight, four and three syllables, so the poem swells slightly in its second line and then tightens. Line two is the slowest, thanks to "suspended", a three-syllable word that makes the line hang as the droplets do. The two short lines that follow feel like a held breath, and the poem stops where the sight is complete. There is no rhyme scheme in the usual sense. Still, "window" and "rainbow" end on the same sound, so the last line quietly answers the first. The light enters at "window" and arrives as "rainbow", and the echo closes the circle without any fuss.
The imagery depends on a contrast the poem never mentions directly. The sun brings heat and brightness, and the shower brings water, and a rainbow needs both. "Droplets" keeps everything small and close. "Suspended" is a still, almost scientific word, and it freezes a moving thing, as though the moment has been paused so it can be examined. Notice how little commentary there is. The poem has hardly any adjectives. It never says "beautiful" or "magical", and it has no exclamation mark and no "I saw". The only trace of the speaker is the possessive in "my shower", which places the sight in a private, domestic space and makes the rainbow feel like something that belongs to one person at one moment. The reader has to supply the delight, and that tends to make the delight stronger.
That is where the poem's significance lies. Rainbows usually carry large associations: storms clearing, distance, something to look up at. Raphen moves one indoors and makes it ordinary, brief and unplanned. The poem suggests that beauty is not rare so much as easy to miss, and that the right response is to notice it rather than to explain it. In its compression it recalls the haiku tradition, though it does not follow a 5-7-5 pattern. The missing full stop may be deliberate. Judging by the form, the poem is left open, as a fleeting sight is: the light may shift at any second and the rainbow will be gone. Even the title, three asterisks, makes the poem feel like a fragment of a longer day, a moment that had to be written down before it disappeared.