An extract from Extraplanar Perspectives on Fio by Khymez Ta’rol.
The mechanism by which earthmotes are transported to Fio is unique among the worlds of the Material Plane. I posit that Caelum’s Light is, in fact, a planar portal with a “hunting mouth.” I hereby coin this term to describe a portal with one or more apertures that move randomly across the multiverse. It is therefore possible for Caelum’s Light to capture earthmotes from other planes every four years, when Fio passes through the tethered aperture.
While the Relief’s foremost scholars postulate that the portal was created to facilitate Caelum’s rise to divinity, I would cite more prominent examples of apotheosis, noting that neither Mystra nor the Dead Three required a portal to ascend. It is more likely that Caelum opened the portal to force his way into Elysium. Furthermore, the fact that the portal still exists today, in my opinion, suggests that it has not yet fulfilled its purpose.