Question M1: Is Maghrib prayer time at sunset or not? What is the definition of sunset in Islam? Is it the time when the solar disc touches the horizon or is the time when the solar disc has completely disappeared below the horizon?
Answer: The definition of sunset in Islam is no different than astronomical definition, i.e. it is the time when the solar disc has completely disappeared below the horizon. It is not the time when the solar disc touches the horizon. However, there is a difference in theoretically calculated sunset and actual sunset. Maghrib time is actual sunset. The calculated sunset is when the sun has just disappeared below horizon to an observer on the surface of the earth assuming earth as perfect sphere and level ground, and assuming some estimated values of temperature, pressure, and humidity conditions in the atmosphere, that affect refraction of light. Maghrib is when looked at the western horizon, the sun just vanishes below horizon with actual effects of refraction, that could change by actual temperature, pressure, and humidity, and the actual ground whether it is sloping downward towards horizon or level ground. Calculations for sunset are done assuming the earth is perfect sphere (which it is not), also assuming that the ground towards western horizon is perfectly level (which may not be), and assuming estimated values of temperature, pressure, and humidity conditions in the atmosphere.
For this purpose at least 3 minutes must be added to the calculated time of astronomical sunset for Islamic sunset or Maghrib. There are 3 reasons for this addition of 3 minutes:
1. The calculations are made at one point by longitude and latitude, and the observer in most cases could be up to 15 miles away from it.
2. The refraction of light through atmosphere whose density keeps on changing due to temperature, pressure and humidity and that changes angle of refraction.
3. There is a possibility of the sloping downward ground towards western horizon, while the calculations are made assuming level ground.
Someone may ask, what would we do if there are mountains and the sun sets behind the mountains for a person who is at the base of a mountain. Is that instant of time OK for Maghrib. The answer is no, because the same person can drive or go up the mountains and see the sun. For mountains regions, the sunset should be calculated as if the monutains are not there, to make sure that no one can see the sun if one is in the valley between the mountains.
