A graphic of the sun going nova.
In an illusion created by Barash for William T. Riker, the Fornax Disaster took place sometime between 2367 and 2383. A star going nova threatened a colony, but the USS Enterprise-D, under Riker's command, arrived in time to save all the colonists.
Jean-Luc Riker, Will's imaginary son, claimed to have been asked about this incident in school by his teacher, Mr. Greenburg, but he did not know the exact stardate. (TNG: "Future Imperfect")