The lyric “How I wonder what you...” is completed by “are” in “Twinkle, Twinkle, Little Star.”
The words began as Jane Taylor’s poem “The Star,” published in 1806 in Rhymes for the Nursery, a collection she produced with her sister Ann Taylor. The familiar opening wonders at the nature of a distant star and compares it with a diamond in the sky.
The melody is older than the English words. It comes from the French tune “Ah! vous dirai-je, maman,” first published in 1761. Wolfgang Amadeus Mozart later used that melody for a set of variations, which helped make the tune especially recognizable.
A common mix-up is confusing the song with “Baa, Baa, Black Sheep” or the alphabet song. All three use the same basic melody, but only “Twinkle, Twinkle, Little Star” contains the line asking what the star is. The full poem has five stanzas, although most people sing only the first.