  Besides a git-based version control system, GitHub integrates several social
coding features. Particularly, GitHub users can star a repository, presumably
to manifest interest or satisfaction with an open source project. However, the
real and practical meaning of starring a project was never the subject of an
in-depth and well-founded empirical investigation. Therefore, we provide in
this paper a throughout study on the meaning, characteristics, and dynamic
growth of GitHub stars. First, by surveying 791 developers, we report that
three out of four developers consider the number of stars before using or
contributing to a GitHub project. Then, we report a quantitative analysis on
the characteristics of the top-5,000 most starred GitHub repositories. We
propose four patterns to describe stars growth, which are derived after
clustering the time series representing the number of stars of the studied
repositories; we also reveal the perception of 115 developers about these
growth patterns. To conclude, we provide a list of recommendations to open
source project managers (e.g., on the importance of social media promotion) and
to GitHub users and Software Engineering researchers (e.g., on the risks faced
when selecting projects by GitHub stars).
