BACKGROUNDThe Sun is the only main sequence star with periodic activities that dominates the Sun-Earth environment and has impacts on human lives. Strong solar activities such as CMEs can affect spacecraft systems, disrupt communications, and even damage ground-based power systems. To understand and forecast the effects of solar activity on Earth’s environment remains one of the main research problems in solar physics. However, our understanding of the fundamental physics of solar activities is still poor. For example, the mechanism of formation of solar cycle variation is unclear so far. In the literature, the Maunder minimum is well-known, and the abnormally depressed solar activity between cycles 23 and 24 has recently started to be discussed. However, their occurrences are big puzzles to solar physicists. On the other hand, the existing observational data are not well calibrated and organized to serve efficient and precise investigations.In particular, long-term observations are needed to study variation of solar activities in multiple solar cycles. Such activities include large-scale eruptions, Moreton waves, sympathetic eruptions, remote brightening [Tang, Moore, 1982], coronal dimming, filament oscillations, and so on. Systematic studies of these large-scale events are essential to understand the topological magnetic structures and hence the eruptive events.The Moreton wave is a disturbance propagated by a wave and generally accompanied by a flare. It was first detected on Hα filtergrams by Moreton, Ramsey [1960]. So far, since Moreton wave events are not commonly observed, it is necessary to proceed to a more systematic analysis by taking advantage of the large Hα data sample all over the world.The planned database is extremely useful in investigating large-scale helicity patterns, which are believed to have a close relationship with solar activities. For example, it can be used to study the possible sign reversal problem in the hemisphere helicity rule. (e.g., [Bao, Ai, Zhang, 2000; Hagino, Sakurai, 2002; Pevtsov et al, 2008]).It is necessary to establish a complete filament catalog in multiple solar cycles. The statistics study of filament properties in many cycles is restricted by discontinuous observations, inconsistent calibration, and incomplete samples from different instruments. It is well known that filaments typically fall into three categories [Hansen R., Hansen S., 1975] according to their latitudes. We pay attention to large-scale filaments in middle and high latitudes as they are high contrast features and their properties are more closely connected with solar cycle problems [Brajsa et al. 1990]. Pevtsov, Balasubramaniam, Rogers [2003] studied chirality of chromospheric filaments, using a limited data set of scanned images from the NSO/SP database. In this project, we further promote the research into solar helicity and chirality problems (e.g., [Martin, Bilimoria, Tracadas, 1994; Rust, Martin, 1994; Pevtsov, Canfield, Metcalf, 1995]), through a complete, unified, and calibrated digitized full-disk Hα data set.