The Great Plume of Agosoria was the religious term used by the Borothan pilgrimage to describe a stellar phenomenon in which a protostar within a stellar nursery gives off a neutron blast, an event which occurs every 11 years. The Borothans believed this to be a sacred event, as it represented the continuing cycle of creation, with the stellar nursery in which it occured being the location where the universe was formed. Groups of Borothan pilgrims would book passage aboard a transport ship to witness the event first-hand.
When the Plume reaches its full brilliance, it is custom to drink a beverage known as voo-sinteel, as it "enhances the experience". Another tradition is the "Invocation of Renewal", a Borothan prayer which the entire group recites during the Plume.
In 2151, the crew of the NX-01 Enterprise also lent witness to this event when Captain Jonathan Archer invited a group of Borothan pilgrims to watch the Plume from the mess hall of the Earth ship. Unfortunately, Archer and several others were unable to enjoy the Plume as it was discovered that Silik, a Suliban, had arrived aboard the Enterprise disguised as a Borothan pilgrim. (ENT: "Cold Front")