On February 15, 2013, asteroid 2012 DA14 passed close to Earth during its flyby. We used this opportunity to analyze how the event affected the social-networking community of Twitter. We analyzed whether the flyby of the asteroid elicited more tweets about the asteroid close to the asteroid's trajectory compared to the neutral search term NASA. A spatio-temporal analysis of tweets about NASA revealed a natural movement of the geographical mean from east to west, mirroring the Sun's path through the sky. For the geolocation of users tweeting about the asteroid, this east-west movement changed direction, mirroring the asteroid's trajectory (from south-east to north-west) as soon as the asteroid was potentially visible from Earth. This effect appears to represent emotionally contagious flocking behavior among Twitter users influenced by the position of the asteroid itself.