Abstract
This study investigates how inquiry-oriented mathematical modeling can support the development of upper secondary students' research skills in astronomy, focusing on the phenomenon of day and night duration. The study presents an instructional approach using a VBA-based Excel tool to calculate day length, solar culmination height, and relative solar energy. The effectiveness of the intervention was evaluated through the quasi-experimental study based on motivational-orientational, operational-activity, and reflective-evaluative criteria. The results demonstrate statistically significant improvements in students' inquiry-related skills, particularly in data interpretation, hypothesis formulation, and reflective evaluation ( p < 0.05; Cohen's d = 1.35). The findings show that 86.4% of students achieved high or medium levels of operational skills, while 90.9% demonstrated well-developed reflective-evaluative competencies. The study concludes that the VBA-based modeling environment effectively enables students to transition from passive observation to active inquiry, bridging the gap between theoretical astronomical concepts and independent data interpretation. This study is framed within the STEM education paradigm, emphasizing the integration of science, technology, engineering, and mathematics in fostering students' inquiry skills.