Impact craters are large holes on the surface of the moon created by the collision of an incoming object. Due to the fact that the moon does not have tectonic activity, water or atmosphere, there is very little erosion of the moon's surface. This means that unlike on Earth, craters are not eroded or worn away. Some lunar craters are estimated to be billions of years old. Scientists have been counting these craters for decades through the use of earth-bound telescopes orbiting probes. Recently, scientists have been employing citizen science to speed up the process - crowdsourcing the data to volunteers. But surely amateurs would be less accurate than professionals?

In a study by the University of Colorado Boulder, the effectiveness of a group of volunteers at identifying craters and other features in a given region of the moon was compared with that of a group of experts, who had between 5-50 years experience. The volunteers were gathered from all over the world and were minimally trained. They were provided with NASA images of different areas of the moon to examine. The results were intriguing. The numbers of craters counted by experts could sometimes vary by as much as 100%, and the variation between individual volunteers was indeed higher than this. However, what they also showed was that when the volunteers were averaged by group, overall the numbers found were within the range of the experts, and pretty close to the average of professors. This means that volunteers as a group identified features of the moon just as effectively as professionals.

Research Scientist Stuart Robbins from the University of Colorado Boulder says "Craters on the moon are important to scientists because they are a record of the cosmic mayhem that went on during the early formation of our solar system. The early solar system bombardment recorded on the lunar surface allows scientists to look backwards in time and see the conditions early Earth likely endured."

The crater counting venture was initiated by CosmoQuest, an online citizen science project that contributes to NASA missions. This was developed by Pamela Gay, an Assistant Professor from Southern Illinois University Edwardsville. The webpage also includes online hangouts, forums and educational features.