But How can Nasa know with these types of certainty that T CrB will probably erupt about the next couple months precisely? It's a matter of mathematical calculations and visible evidence. By way of example, the final time T CrB experienced a nova was in 1946 – 78 years back. https://econopass.com/news/science-technology/get-ready-for-a-stellar-show-nasa-predicts-summer-2024-nova-explosion/