An anonymous reader shares a report: On the night of March 11, 1437 A.D., in what is now modern-day Seoul, a new star appeared in the sky, seemingly out of nowhere. The newcomer shone for 14 days before fading into the darkness. Korean astronomers noted the mysterious star and its brief stint in the sky in their records. Centuries later, modern astronomers studying these records determined that what the Koreans had seen was a cosmic explosion called a nova. Novae occur in two-star systems, when a dead star, known as a white dwarf, starts eating away at its companion, a star like our sun. The white dwarf slowly builds a layer of hydrogen stolen from the other star over tens of thousands of years, and then ejects it all at once, producing an eruption of light 300,000 times brighter than the sun that can last for weeks. Michael Shara and his researcher colleagues have spent the last nearly 30 years looking for the star responsible for this nova. In a new paper published Wednesday in Nature, they say they've finally found it. "It's been like searching for a needle in a billion haystacks," Shara said. For most of their search, Shara, a curator in the American Museum of Natural History's department of astrophysics; Richard Stephenson, a historian of ancient astronomical records at Durham University; and Mike Bode, an astrophysicist at Liverpool John Moores University, focused on a part of the sky where they suspected the mystery star must lurk. The investigation was an on-again, off-again effort of "failure after failure after failure," one that they returned to when they had the time or a lead. Last year, Shara found some relevant files in his office that he hadn't looked at in nearly a decade, and decided to expand the search area in the sky. He started combing through digital databases of stars, looking for any interesting targets. In one astronomical catalog, he saw a well-known planetary nebula, a glowing shell of gas and dust. In a different catalog, he found an image of a binary star taken in 2016 in the same area. Then it hit him: That wasn't a planetary nebula. It was the leftover shell of a nova explosion, floating near the star system that produced it.