Time Fix for Asar Prayer

When the time of Zuhr prayer ends, the time for Asar prayer starts. When the shadow of an object becomes twice its size, plus its original shadow, it is best time for Asar prayer. This time lasts until the sun sets. Then the sun gets lowered quite a lot, loses its brilliance and turns yellowish, the prayer of Asar becomes undesirable. It should, therefore, be offered before this happens.