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Taru Seco is a binary star system consisting of Taru Major, slightly larger than Golarion's sun, and Taru Minor, only half its size, orbiting each other. After Cynosure, Taru Major and Taru Minor are the second and third brightest stars in Golarion's sky.1
Taru Seco's binary nature is easily visible from Golarion with a rudimentary telescope. It features in the legends of various cultures, even those without telescopes, due to the mystery of its variable apparent brightness.1
During the time of Azlant, an expedition was launched to the hot planets orbiting Taru Major. The Azlanti discovered the bizarre, immense ruins of an advanced humanoid civilisation on par with Azlant itself, but no signs of their inhabitants. On the third day, some explorers began to mysteriously vanish despite various magical protections, and the rest quickly fled home.1
It is believed that the Lirgeni discovered Taru Seco's mystery in their final days, but their country was destroyed by the Eye of Abendego, leaving behind cryptic clues that Taru Major and Taru Minor orbit an unknown mass between them, and warnings about 'the worm within the apple'.1