Main Belt asteroids are commonly select as targets for studies. These are the ones often well placed in the sky for observing campaigns. They might be selected as part of a study of a family of asteroids, as part of a search for binary asteroids, or to try to improve the statistics of the asteroid database by eliminating observing biases.
Over time, many observers have only published results on the easier asteroids to observe. These include the fast rotators - those which an astronomer can observe an entire rotational period in a single night. For long-period asteroids, many amateur astronomers have difficulty linking one night's data to the next. Different comparison stars are used giving wildly different results from one night to the next. The analysis software used at CS3 is MPO Canopus, which contains a subset of the 2MASS star catalog which has been converted to a standard system. By using 2MASS catalog stars approximating the color of asteroids, each night's work can be reasonably linked to any other allowing the creation of lightcurves that span many nights or weeks.
By following up on bright asteroids for which no period has been reported, many long-period asteroids have been found. It is now thought that approximately a quarter of the Main Belt asteroids have a rotational period weeks or days in length. New theories now need to be created to account for this abundance.