How can the White Days of each month be determined for fasting, especially with the variation in the Hijri date between countries, and what exactly are the White Days?

The jurists have agreed upon the recommendation of fasting three days of every month. The majority of scholars have gone to the recommendation of these being the Ayyam al-Bid (the White Days), which are the thirteenth, fourteenth, and fifteenth of every Hijri month, based on what has been narrated from the Prophet, peace and blessings be upon him. However, the Malikis disliked fasting them for fear that their obligation might be believed. They were named "white" due to the whiteness of their nights from the moon. Their determination is made by knowing the beginning of the Hijri month, either by sighting the crescent moon or by completing the previous month to thirty days.