UNITY

Why determining the start and end of Ramadan by Calculated Crescent-Visibility is perfectly legitimate according to the Shari’ah.

Dr Usama Hasan

Fellow, Royal Astronomical Society (UK)

29^th Sha’ban 1447 H

17^th February 2026 CE

THE ZUHAL ESSAY SERIES: NO. 1

Contents

1. The Plain Truth About This Matter
   
2. Classical Muslim Jurists Who Allowed Calculation For Moonsighting 4
   
   2.1 Imam Nawawi’s commentary on “If it is obscured by cloud, then determine for it.” 4
   2.2 Ibn ‘Arabi’s commentary on “If it is obscured by cloud, then determine for it.” 4
   2.3 Imam Ibn Daqiq al-‘Id supported the use of calculations 5
   2.4 Imam Subki supported the use of calculations 5
   2.5 Imam Ibn Taymiyyah rejected the use of calculations because they could never be accurate enough 5
   2.6 Ibn Hajar al-‘Asqalani’s discussion, quoting multiple authorities 5
   2.7 Shaykh Ahmad Shakir 8

3 Answers to Objections to the Use of Calculations to Replace Moonsighting 9

3.1 Hilal means a public matter, from its name 9
3.2 The Prophet ﷺ said: We are an unlettered (ummi) nation: we do not calculate or write 10
3.3 “Witnessing the month” can only be done via seeing the hilal 10
3.4 “Enter houses from their doors” 10
3.5 Calculations are only “in someone’s head” 11

4 A Brief History of Moonsighting Calculations 11

4.1 Medieval and modern methods 11
4.2 Modern methods 13
4.3 Modern prediction criteria 13
4.4 HMNAO’s method: the Yallop Criterion 13
4.5 Crescent-visibility curves 14
4.6 World record crescent sightings: naked-eye, telescope & CCD-imaging 15

5 Using Calculations for Crescent-Sighting, just as for Islamic Prayer Times 15

Table of Figures

Figure 1: Calculating Crescent Visibility 12
Figure 2: Crescent-visibility curves for Ramadan 1429 H / 2007 CE 14

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