How are the times for Asr and Isha' calculated?

Answer

The times for Salaat have to be determined by observing the decrease and increase of the shadow of an object and other natural phenomena. The shadow of a stick or of anything is the shortest at the time of Zawwaal. For example, the Fay-e-Zawwaal (shadow at Zawwaal) of a metre stick is 4 centimetres on a certain day. Now when the shadow has reached 2 metres and 4 centimetre's, then Zuhr time expires and Asr time begins.

Isha' time begins when the Shufuq Abyadh (the white glow) which comes after the red glow, disappears from the western horizon.