Sky brightness and twilight measurements at Jogyakarta city, Indonesia

International Symposium on Sun, Earth, and Life

物理学;天文学;生物科学

Herdiwijaya, Dhani^1

Astronomy Research Division, Bosscha Observatory, Institut Teknologi Bandung, Ganesha 10, Bandung

40132, Indonesia^1

关键词: Area measurement;    Brightness measurements;    Light pollution;    Mean values;    Spectral range;    Temperature fluctuation;    Temperature variation;    Temporal resolution;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/771/1/012033/pdf
DOI  :  10.1088/1742-6596/771/1/012033

来源: IOP

【 摘 要 】

The sky brightness measurements were performed using a portable photometer. A pocket-sized and low-cost photometer has 20 degree area measurement, and spectral ranges between 320-720 nm with output directly in magnitudes per arc second square (mass) unit. The sky brightness with 3 seconds temporal resolutions was recorded at Jogyakarta city (110° 25′ E; 70° 52′ S; elevation 100 m) within 136 days in years from 2014 to 2016. The darkest night could reach 22.61 mpass only in several seconds, with mean value 18.8±0.7 mpass and temperature variation 23.1±1.2 C. The difference of mean sky brightness between before and after midnight was about -0.76 mpass or 2.0 times brighter. Moreover, the sky brightness and temperature fluctuations were more stable in after midnight than in before midnight. It is suggested that city light pollution affects those variations, and subsequently duration of twilight. By comparing twilight brightness for several places, we also suggest a 17° solar dip or about 66 minutes before sunrise for new time of Fajr prayer.