Visual Comparison of False Dawn and True Dawn Based on Digital Imagery and Linear Brightness Analysis Shindu Irwansyah, Fahmi Fatwa Rosyadi Satria Hamdani, Maman Surahman
Universitas Islam Bandung
Abstract
The determination of Subh (dawn) prayer time in Islam depends on distinguishing Fajr Kazib (false dawn) from Fajr Sadiq (true dawn), a differentiation that holds both religious and astronomical importance. Fajr Kazib appears as a brief vertical light and does not mark prayer time, while Fajr Sadiq is a stable horizontal glow along the eastern horizon that signals the permissible start of Subh prayer. However, identifying these phenomena can be difficult due to atmospheric interference, light pollution, and subjective perception. This study investigates their visual characteristics using digital image analysis and a linear brightness curve method. A qualitative approach was applied, involving systematic sky observations with DSLR cameras and luminance measurements using a Sky Quality Meter (SQM). Observations were aligned with solar depression angles from -20 degree to -15 degree. Results show that Fajr Kazib typically appears at -20 degree to -17 degree, marked by faint, vertically oriented light. Fajr Sadiq, emerging between -18 degree and -15 degree, is characterized by a consistent and broader horizontal illumination. The linear brightness curve confirms these findings, showing a sharper decrease in darkness as Fajr Sadiq begins. The study demonstrates that combining digital imaging with observational astronomy enhances accuracy in identifying prayer times, offering a more objective method to determine the true onset of Subuh.
