Zooniverse runs The Milky Way Project which aims to classify and measure the galaxy. Zooniverse founded the Citizen Science Alliance which collaborates with academic institutions using volunteers to sift scientific data.
The website consists of infrared images from the Spitzer Space Telescope which is mapping the Milky Way. After watching a brief and simple tutorial, volunteers draw circles on a small section of the on-screen images to record or discuss what they have spotted. All the data is analysed by scientists, so don’t worry about making mistakes.