This research aims to create a learning trajectory by using Ramadhan tradition in Pemalang as a context to assisting students in recognizing the concept of sine rule. The approach used in this research was Realistic Mathematics Education. The subject of the study is the tenth-grade students of SMA N 1 Belik, Pemalang, Jawa Tengah, with six student participants who have been chosen as heterogeneous students. The methodology used is design research consisting of three stages, namely preliminary design, design experiment, and retrospective analysis. Nonetheless, this analysis only shows the results of the design experiment stages, in particular, the pilot experiment. Data collection was carried out using a variety of methods, namely: video recordings, photos, student work results, and student interviews during online learning. Student learning activities comprise three activities: observing night market video to find facts about the triangle, observing Takbir keliling video to find the concept of the sine rule, and solving a contextual problem related to the sine rule. The results of this study show that a series of activities designed could help students understand the concept of sine rule by using skype as a media and Ramadhan tradition in Pemalang as a context.