Daily, Muslims are obliged to pray five times. All prayer obligations have a set time, marked according to the apparent sun's diurnal journey. Two of the five obligatory prayers are at the onset of the morning twilight for the beginning of the fajr prayer and the isha prayer's end of evening twilight. However, various countries use different criteria to determine the beginning of the morning twilight and the evening twilight. For example, the United States uses a sun depression angle of -17.5 degrees for the onset of the morning twilight and -15 degrees for the end of evening twilight. Egypt uses -19.5 degrees and -17.5 degrees, and Saudi Arabia uses -18.5 degrees and 90 minutes after sunset. Meanwhile, European countries generally use the Muslim World League criteria of -18 degrees and -17 degrees. Several countries in the ASEAN region, including Indonesia, use -20 degrees and -18 degrees.The difference in the use of the sun depression angle for fajr and isha has raised suspicion. How could the appearance of the first detected sun's rays in the morning be different from the vanish of the sunlight at night when the earth's radius was the same in all directions? Furthermore, how could the first detected sunlight in Europe be different from that in the Equator region when it refers to the local horizon? While the earth's radius is the same in all locations. The atmosphere thickness in the higher latitude is different from that of the equatorial area; however, the difference must not create such a big gap. Of course, the twilight range (from the beginning of the twilight to the sunrise) in high latitudes (Europe and America) is different from in the equatorial region. It is primarily because the apparent sun travels more diagonally at high latitudes. However, the sun's depression angle to mark the beginning of the morning twilight should be the same everywhere over the globe. So the stipulation of the sun's depth for the starting of the morning twilight and the end of the night twilight seemed to be done randomly without using accurate astronomical and physical data.As it is concerned with the punctuality and the worship quality of some 1.8 billion Muslims globally, the Islamic Science Research Network (ISRN) has researched the 980 morning and evening twilight data. Although their distribution is not even, the sample data have covered four continents, excluding Australia. This book reveals its results. We organize the book into seven chapters.