Different Prayer Schedule

Assalaamu Alaykum,

Thank you very much for raising a very pertinent and important question.

The difference in Fajr and Isha timings in our masajid in the same city comes from using different criteria. Some use 15 degrees of the sun’s depression and others use 18 or even 20 degrees of sun’s depression. In some places people use 75 or 90 minutes criteria. Both methods have their validity among scholars and you can choose based on your preference

The Quran and the Sunnah did not prescribe any degrees of the sun’s depression as the Quran said eat and drink until the white thread of dawn appears to you distinct from its black thread, then complete your fast till the night appears.(2:187)

The Sunnah guides the believers to offer Isha at the disappearance of shafaq.  Scholars have differences on the meaning of the term and these differences are the main reason for adopting different methods to determine prayer timings for Fajr and Isha.

Those who follow 15 degree of sun depression method follow nautical twilight where the horizon is closer to sea level because its visibility is not possible to determine a latitude with reference to the horizon.

Those who follow 18 degree criteria follow astronomical twilight where there is no light and it is dark with no perception of twilight.

However, NASA defines astronomical twilight. “Before the beginning of astronomical twilight in the morning and after the end of astronomical twilight in the evening the sun does not contribute to sky illumination; for a considerable interval after the beginning of morning twilight and before the end of evening twilight, sky illumination is so faint that it is practically imperceptible”

We can conclude on the basis of above discussion the following

Fajr:
Subh Sadiq (Fajr-al-Mustatir) when morning light in the sky starts spreading horizontally  

Sunrise:
When the top of the sun's disk just appears above the horizon.

Zuhr:
When the sun begins to decline after reaching its highest point (Zenith) in the sky. 5 minutes after Zenith.

Asr:
When the length of any object's shadow reaches a factor of the length of the object plus the length of that object's shadow at Noon.   

Sunset:
Theoretical time as given in newspapers when the top of the sun's disk just disappears below the horizon.

Maghrib:
For Sunni's, it is 3 minutes after theoretical sunset; for Shi'aas it is 17 minutes after theoretical sunset.

Following are help notes from IslamiCity Prayer times Application:
http://www.islamicity.org/PrayerTimes/

Calculation methods allow you to apply a convention on which angle to use for calculating the Fajr & Isha time and shadow factor for Asr time. 

Edited by Dr. Aslam - 02 March 2018 at 10:28pm