"He (Allah) it is that cleaves the daybreak (from the dark): he makes the night for rest and tranquility and the sun and moon for the reckoning (of time): Such is the judgment and ordering of (him), the exalted in power, the omniscient, . (Q6: 98)
The Islamic year is a lunar year, i.e. a year based on the phases of the moon. One complete cycle of the moon takes roughly thirty days and there are twelve of such cycles as ordained by Allah;
"the number of months in the sight of Allah is twelve in a year so ordained by Him the day He created the heavens and the earth; of them four are sacred; that is the right religion" (Q9:36).
Know that using any other calendar amounts to a step away from "the right religion". Worse, it makes you unaware of certain days of critical importance during the Islamic year.
Since the Islamic calendar is lunar, the months are not fixed to a particular season. Every 33 years, all the months of the Islamic calendar go through the different seasons in a full cycle. This ensures that Ramadan, the month of fasting, is not fixed in any particular season. Had it not been for this, some countries would have found it easy to fast If Ramadan fell only in the rainy season while others would have found it perpetually difficult if Ramadan fell only in the dry season. If Ramadan falls in December in one year, fifteen years from that year it would fall in July while in thirty years it would fall again in December. You can see there's much good sense and equity in that.
This article was culled from the publications of Deen Communication Limited