This page will focus on lines 225-28 and Fredrick L. Hildebrand's brief discussion of it within the context of his thesis: that Shelley was interested consistently in the cataclysmic theories involving comets.
Here are lines 225-228:
But She, whom prayers or tears then could not tame,
Past, like a God throned on a winged planet,
Whose burning plumes to tenfold swiftness fan it,
Into the dreary cone of our life's shade [...]
Hildebrand writes:
In this poem Shelley uses the collision of a comet with the earth to depict the cataclysmic events which throw an individual, society, and the universe into a state of chaos and to represent his thoughts about the processes that will result in their restoration. In his reading Shelley found at least two cataclysmic events in which comets were thought to have wreaked havoc on the world. Garbo and King-Hele mention the old belief discussed by Darwin in the Botanic Garden (II .ii. 77-82) that the moon was torn from the side of the earth. During Shelley's time this theory had not been discredited. Garbo notes that Lebnitz, Whiston, Davy, and others believed that the attractions and collision with a comet was also responsible for the Flood. Shelley suggests this possibility in his explanation of the disaster which exterminate the dinosaurs in Prometheus Unbound (IV, 308-318), attributed either to a flood or a God throned in a comet. In Epipsychidion he draws on such scientific theories to create a controlling metaphor that emerges personal, social, and universal crises. (77)
Hildebrand, Fredrick L. "Epipsychidion's Cosmic Collision: A Controlling Metaphor." Keats-Shelley Journal 37: (1988): 75-90.