When exploring the subject of how to establish Subh al-Sadiq (dawn), the entrenched position of using the depression angle of 18° is powerful one due to its use over many hundreds of years across the Islamic World, and rightly so.
It was clear to the project coordinators that it was critical to explain why the depression angle of 18° was an effective method of approximating Subh al-Sadiq (dawn) for those locations nearer to the equator but why other considerations come into play especially in northern latitude countries.
In April 2016 a paper was published on the subject. This paper also introduced the concept of measuring twilight to establish Subh al-Sadiq (dawn) rather just assuming the depression angle of the sun results an a fixed level of twilight which can be observed.
Publication : Establishing Dawn: Challenges & Opportunities for Muslims in Northern Latitudes