The reference to the false dawn (al-subh al-kadhib) in hadith to define when Fajr does not start has led some Islamic scholars to take the position that the false dawn (zodiacal light) point must be established as a precursor to defining Subh al-Sadiq (dawn).
For northern latitude countries like the UK and with the general level of global pollution, many astronomers now believe seeing zodiacal light is almost impossible during the majority of the year. A number of studies have indicated that zodiacal light may still be visible at the spring and autumnal equinox which occurs around the 20th March and 22nd September respectively.
The Sky Quality Meter (SQM) allowed the project to record what could be considered al-subh al-kadhib - the false dawn. During the 15 months of continous data logging, the SQM was able to record a number of days in late March and late September (spring and autumnal equinox) where the magnitudes per square arcsecond (MPAS) would dip before levelling off of a period of time after which the MPAS reading would then start to decrease as a given rate towards sunrise.
This sudden decrease in MPAS readings followed by a period where it remains the same is most likely the burst of twilight which results at al-subh al-kadhib. This twilight does not increase but spreads across the horizon before Subh al-Sadiq begins. The following two charts are examples of these MPAS readings. The point at which the sun is at the depression angle of 15° has also been shown.
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