Abstract Microblogging is a form of online communication by which users broadcast brief text updates, also known as tweets, to the public or a selected circle of contacts. A variegated mosaic of microblogging uses has emerged since the launch of Twitter in 2006: daily chatter, conversation, information sharing, and news commentary, among others (Java et al, 2007). Regardless of their content and intended use, tweets often convey pertinent information about their authors mood status. As such, tweets can be regarded as temporally-authentic microscopic instantiations of public mood state (O`Connor et al, 2010). Here we perform a sentiment analysis of all public tweets broadcasted by Twitter users between August 1 and December 20, 2008. For every day in the timeline, we extract six dimensions of mood (tension, depression, anger, vigor, fatigue, confusion) using an extended version (Pepe and Bollen, 2008) of the Profile of Mood States (POMS), a well-established psychometric instrument (Norc...