Two different types of disk-integrated photometry are used: (i) dense-in-time, which typically consists of tens to a few hundreds of individual data points observed during one revolution (typically several hours), and (ii) sparse-in-time, where the typical separation of individual measurements is large compared to the rotation period. For sparse data, we usually have a few measurements per night in a particular sequence (e.g., for data from the Catalina Sky Survey project, where there are typically four individual observations separated by ∼20 minutes). By sparse-in-time data, we usually mean photometry produced by large astrometric sky surveys. There is no proper boundary between dense and sparse data, because one can create an observational strategy that is in some aspects similar to both dense and sparse data. Based on the type of the photometry, we use the terms “dense lightcurves” and “sparse lightcurves”.

Dense data well define the rotational period. These lightcurves are typically observed by many “backyard“ observers, but also by professionals, who, for example, dedicate their observational campaigns to particular asteroid groups.