Lecture 1: ''The Scientific Citizen' In the first of this year's Reith Lectures, entitled Scientific Horizons, Martin Rees, President of the Royal Society, Master of Trinity College and Astronomer Royal, explores the challenges facing science in the 21st century. We are increasingly turning to government and the media to explain the risks we face. But in the wake of public confusion over issues like climate change, the swine 'flu vaccine and, more recently, Iceland's volcanic ash cloud, Martin Rees calls on scientists to come forward and play a greater role in helping us understand the science that affects us all.