Tabby’s Star – also known as KIC 8462852 or the “alien megastructure” star – is at it again. And this time the world is watching. The star in the constellation Cygnus has intrigued astronomers for a year and a half because they can’t quite explain why it periodically dims. One hypothesis is that aliens are building an energy-generating Dyson sphere around the star, but less way-out possibilities include cometary storms or blobs of circumstellar material. This week, a team on the Canary Islands detected unusual readings from Tabby’s Star, just in time to alert fellow astronomers around the world to turn their telescopes toward it.