RR Tauri is an incredibly active young stellar object -- a star still in the process of forming. RR Tau is an emission-line star belonging to the HAeBe class, which are stars with spectral types A or B, emission lines, and show signs of nearby nebulosity. It is also a variable star belonging to the UXOR (or UX Orionis) class. UXORs probably vary due to occasional obscuration by material in the clouds from which they're still forming, although the exact mechanism isn't clear. Its variations are unpredictable and are not periodic; RR Tau can change from rather sedate variability to violent variations of several magnitudes in the span of just a few days.