 Over the past two decades, citizen science has undergone a period of rapid growth. Citizen scientists are people who are not paid to carry out scientific research, but who make intellectual contributions to scientific research nonetheless. And perhaps some of the biggest contributions are currently being made in the field of astronomy. Studying the night sky is a tremendous task. Even with the most advanced technology, scientists have mapped only a tiny fraction of the observable universe. And even within that tiny fraction, there are billions and billions of objects that await discovery and classification. The point at which human review of data is no longer necessary has been forecast for decades. But the number of problems for which the manual review of images or data is still carried out is considerable. Luckily, scientists don't have to go at it alone. Armed with equipment that, at worst, is a scaled-down version of what you'd find in an astronomer's toolkit, and at best is as good as the real thing, the general public is helping scientists tackle some of the biggest problems in astronomy. This is citizen astronomy, and it is being driven by the ease with which people can form communities and work together via the Internet. Citizen astronomy dates all the way back to the early 1700s, when Edmund Haley, the famed English astronomer for whom the comet is named, asked people across England to observe a total solar eclipse, whose shadow he predicted would cross through the center of the country. These amateur astronomers are well equipped to do more than gaze at the night sky with the naked eye. Indeed, a number of very productive pro-AM collaborations have formed to observe a variety of bright astronomical objects in ways that capitalize on the flexibility, availability, and skill of the amateur observing community. Professional-led visual classification projects have appeared, attracting thousands more citizens to the field than were previously engaged in amateur observational research. To foster continued success in astronomy, it's important to understand what motivates citizen astronomers and what makes for a successful citizen astronomy project. The varied interests and skills of citizen astronomers make for a rich diversity of research projects within the citizen astronomy universe. Among the most successful are Galaxy Zoo and the American Association of Variable Star Observers, or Avso. Surveys of volunteers participating in these projects suggest that most citizen astronomers are motivated by the same desire that drives many professional astronomers, the desire to contribute to science or simply be involved in science and research. Part of what has made Galaxy Zoo the most prominent scientific crowdsourcing project to date is the project's appeal to this fascination. Galaxy Zoo offers participants the chance to be the first to see a galaxy they're asked to classify based on shape. Similarly, Avso offers volunteers the opportunity to analyze data or help manage the association's enormous database. From a technical perspective, projects like Galaxy Zoo and Avso have been so successful because they fill an important niche in astronomical research. Even the best automated software designed to observe and classify objects in the sky is no match for the human eye. Citizen astronomy itself remains, in many ways, an ongoing project, a project in understanding how best to harness and nurture the public skills and abilities for the advancement of science. Given the steady progress made so far in a field with tantalizing discoveries yet to be made, many consider citizen astronomy a project well worth pursuing.