みさと天文台における「夜空の明るさ」の長期変動 : SQM-LEによる4年間の測定結果の分析

This paper reports on the analysis of four years of Night Sky Brightness (NSB) measurements obtained with an SQM-LE at Misato Observatory. The data, collected from September 24, 2021, to April 23, 2025, were classified and analyzed into two categories: "Nighttime" and "Conditions suitable for stargazing". The analysis revealed that while the year-to-year NSB variation was very small, the hourly variation was larger than the yearly or monthly differences. Specifically, the "Nighttime" data showed that the sky became 0.45 mag/arcsec² darker between 20:00 and 3:00, and the "Conditions suitable for stargazing" data showed a darkening of 0.82 mag/arcsec² between 18:00 and 5:00. This suggests that the light pollution at Misato Observatory has remained stable over the long term.