Sor Juana Inés de la Cruz long poem Primero sueño is pregnant with references to astronomy and astrology. Starting with the hypothesis that Sor Juanas hermetic allusions throughout her masterpiece were inspired by her observation of a lunar eclipse on the22nd of December, 1684, Américo Larralde produces an in-depth analysis of the poem where science and literature blend, expounding upon the many meanings conveyed in the greatest work of Latin-American baroque literature.