Dusk and Dawn in Medieval Islam: on the Importance of Twilight Phenomena with Some Examples of Their Representations in Texts and on Instruments

Dusk and dawn are one of the most important astronomical phenomenon used in Islamic ritual worship. They are connected with two of the five pillars of Islam, the fasting in Ramadan, and the ritual prayer. They are to be performed at the right time to be accepted. To know about dusk is necessary in Ramadan to determine the end of fasting, and about dawn to determine the beginning of fasting ‘when a white thread may be distinguished from a black’ (Sura 2,187). Further they are in need of determining three of the five daily ritual prayers in Islam, the evening prayer, the night prayer and the morning prayer. All of them are defined by twilight phenomena. These prayers rest on the Qur'an (see Sura 11,114, Sura 17,78 and Sura 50,39f) and the Sunna, the Hadith collections with the acts and sayings of the Prophet Muhammad. These collection contain different descriptions or definitions of these prayer times. Most of them are phenomenological, for example ‘Do the morning prayer when the stars become indistinct!’ (Malik, Muwatta’, Wuqut al-salat, Wuqut al-salat (no. 6)). According to their position in Islamic religious duties dusk and dawn were widely discussed in different medieval Islamic astronomical sources, in texts and on instruments. On the one hand, in an astronomical tradition often called mathematical, the definition of these prayer times by twilight phenomena lead to exact and approximative methods to calculate time and duration of twilight by the angle of the solar depression below the horizon. These values are represented in tables and on instruments, especially on astrolabes. On the other hand texts on time keeping and the determination of the Qibla, the sacred direction in Islam towards Mecca, not written for the astronomical expert and probably produced in a legal context, so called folk astronomical texts, deals with the time and duration of twilight in two different kinds. First, there are rough approximative methods of determining the beginning, duration and end of dusk and dawn by the Lunar Mansions using them as a 'star clock'. Second, these texts contain detailed descriptions of the twilight phenomena in the morning and in the evening probably based on observations which are very useful to interpret the definitions given in the Hadiths. These descriptions are a beautiful example of an astronomical phenomenon which influenced the ritual worship of one of the three great monotheistic religions.