The continuous data logging of light level readings (magnitudes per square arcsecond - MPAS) from sunset to sunrise the following morning, allowed the study to establish the first point at which the sky begins to get brighter; the tipping point. Subh al-Sadiq (dawn) cannot occur before this point and occurs at some point after this tipping point as the SQM is more sensitive than the human eye.
The following chart is an illustration of this principle. The MPAS reading remains at around 20 MPAS during the night of the 8th May 2018. At a given point (3AM BST) the introduction of a light source, i.e. the sun begins to result in a decrease in the MPAS reading. The first point at which this decrease occurs and continues to drop, in this project is defined at the tipping point. As the SQM is more sensitive than the human eye, Subh al-Sadiq (dawn) must be occurring after this point.
The following chart show the tipping points (Blue Dots) for a 12 month period in the city of Leicester (UK). Along with the established tipping point for each day, the corresponding time at which the sun is at the depression angle of 18°, 15° and 12° is also shown. The mathematical LOWESS function has been applied to the varying tipping points to establish a curve through the values as is shown as a red line.
All times have been shown in GMT. During British Summer Time (BST) plus one hour is added to all times shown.
[Click Image to Expand]
What the tipping point analysis shows:
- There is no fixed point at which dawn can occur. This is explored further in the Impact of Climate section
- Subh al-Sadiq (dawn) can occur at any time within a period (maximum and minimum point)
- Tipping point data indicates dawn occurs much later than 18°
- Tipping point data indicates that Subh al-Sadiq (dawn) does not occur before 15° (maximum)
- Any Subh al-Sadiq (dawn) time between 15° (maximum) and 13° (minimum) seems supported by the tipping point data
- The time of Subh al-Sadiq (dawn) can bedetermined throughout the year hence no alternative method is required