SUMMARY
This study aims to develop a learning trajectory by using the context of the Megono Gunungan tradition to help students grasp a sphere's notion. Indonesian Realistic Mathematics Education (PMRI) was the approach taken in this study. The subject of this research was third-grade students of SMP 38 Semarang, Central Java, Indonesia. The methodology used consists of three stages of design research developed by Graveimeijer and Cobb, namely preliminary design, design experiment, and retrospective analysis. Several techniques were used for collecting data, namely video, photography, the outcome of students' worksheets, and student interviews. The learning trajectory comprises four activities: identifying sphere components using the Megono Gunungan tradition interactive video context, discovering the sphere surfaces area using orange fruit, finding the sphere's volume through rice media, and solving problems of the sphere. This study's findings showed that the use of the Megono Gunungan tradition context could encourage learners to recognize the notion of the sphere through a sequence of designed activities.