The Vanishing and Appearing Sources during a Century of Observations (VASCO) project has found around 100 stars that have disappeared without explanation over the last 70 years. The project compared images from the US Naval Observatory and the Pan-STARRS sky survey. Theories for the disappearances include stars collapsing into black holes, gravitational lensing, gamma-ray bursts, or asteroid movement. The search also aimed to find a hypothetical Dyson Sphere, a method advanced civilizations could use to harness star power.