Question: A Christian sister of mine asks, "Why is it that only Muslim festivals vary from country to country? Do you not have an accurate method of calculation?" I hope you can provide a suitable explanation.
– A. Jamruth Azeez, Kodungaiyur.
Explanation: It is not just Muslim festivals; other festivals also vary across countries. That is simply how the world is structured. We know that different regions of the world experience different times; when it is day in India, it is night in half of the rest of the world.
People in other regions can only celebrate a festival—which we celebrate during the day—after we have already entered the next day. Everyone could observe a festival at the exact same time and on the same day only if the entire world shared the same time zone.
This also answers the question regarding whether there is an accurate calculation method.
Islam does not instruct us to rely on calculations; instead, it directs us to celebrate festivals based on the sighting of the new moon.
Let us assume, for the sake of argument, that we followed a calculation method as the Christian sister suggests. Even then, it would be impossible for the entire world to celebrate any festival on the same day.
Suppose calculations indicated that a festival falls on this morning for us. People in a country like the USA—where it is currently night—would only be able to celebrate that festival the following morning; they could not celebrate it at the same time we do.
The world is structured in such a way that it is impossible to perform any activity simultaneously across the globe. Such a thing would only be possible if two suns were positioned on opposite sides of the Earth. Christmas cannot be celebrated in the USA and India on the same day and at the same time; nor is it celebrated that way.
While we claim it is the same date—due to the 'Date Line' established by humans—in reality, the celebrations take place on consecutive days. When the New Year begins in America at midnight, we—who are experiencing broad daylight at that same moment—do not celebrate it.
If this is understood, people would not criticize the fact that Muslim festivals fall on different days.