The comet is a phallic symbol, a fact that may confuse us since it supposedly signifies Emily. Richard Homes writes:
The identity between male and female, or at least the transposable or interchangeable elements between the two sexes had long been an under-theme of Shelley's writing. The masculine role frequently assigned to his heroines like Cytha or Asia, the passivity of his male lovers like the poet of Alastor, is one of the constant and original features of his poetry. With his work on The Cenci, Shelley showed signs of developing this feature further into the realization and acceptance of certain elements in his own personality and temperament. Again, the importance of the play lies in its character as a psychological documentary. In later poems, especially "The Witch of Atlas" and Epipsychidion, he was to pursue questions of bisexuality and androgynous creative powers with more deliberation. (517)
Holmes, Richard. Shelley: The Pursuit. London: Weidenfeld and Nicolson, 1974.