For example, the amateur Skywatchers in the web-based Milky Way Project have classified more than 1.5 million objects in the Milky Way Galaxy. Zooniverse's 11,000 members have contributed to more than 70 scientific papers and the discovery of a class of compact galaxies. Planet Four's 122,000 participants have classified more than 4.5 million images from the surface of Mars. starts with the basics. It explains how and why the sky changes during the night and through the seasons. It gives practical advice on what equipment to choose and describes what you can expect to see. There are also plenty of tips for observing just with the naked eye. The book includes: is an invaluable reference source for astronomers of all levels.