The vast shadow of Saturn's largest moon Titan will fall upon the upper extreme of the ringed gas giant in the early hours of Sept. 20, just one night before the planet shines at opposition in Earth's sky.
Once every 15 years, the orbital mechanics of the solar system brings the orbital path of Titan into an edge-on alignment with Earth, opening a brief window during which the moon's colossal shadow can be spotted periodically sweeping across the surface of the gas giant.
