every hour of every day, a growing armada of earth observation satellites are peering down on our planet, gathering petabytes of images and data about our changing world. a new online course from the Open University's super slick Future Learn site lets you take a more detailed look at these incredible spacecraft, and explore how the information they collect is used. it's free and the first online course from the European Space Agency, so sign up if (like us) you're interested in how space technology can help save the planet