Since early in Man's history there has been a need to accurately tell time. Time is relative. It is relative to the spinning of the earth around the sun and even the orbit of the sun itself. If you were to stop all this we would not have time. Our universe is full of cylcles and nothing is still even if we think it is. This procession of life is like a strip of film though which are souls are exposed to in sequential order giving us the perception of time as the events around us unfold in order.
All that may be the essence of what time really is but when it comes to how we should tell time here on earth and how to be in line with the Quran we find ourselves in a predicament. It's not that serious of a predicament, but it is a predicament that can be hard to work our way out of. We find ourselves in this predicament because of wrong information. The Quran give us some basic information on how to reckon time. The day starts with the appearence of daylight, so that 1 whole day is from dawn to dawn, not dusk to dusk like the Jewish and Islamic calendar. A month is, according to Quranic preference 30 days. 2:184 says that 1 day of missed fast can be compensated for feeding 1 person, then later on in the Koran in chpt. 58:5 it is stated that the compensation for missing 2 months worth of fasting is to feed 60 people.
This, through logical consideration means that the Koran obviously equates 2 months with 60 days, and 1 month with 30 days. Some may think that 5:89 contradicts this equation. It says that the compensation for breaking deliberate oaths is to serve 10 needy individuals from the best of what you would feed a family member of yours, to clothe these 10 individuals, or to free someone from bondage. If none of these is within the capability of the individual then he is to fast for 3 days. There is no compensation for this fasting, this is the last thing that can be accepted of him. But why isn't there a one-to-one relationship here between feeding individuals and fasting? Because the fasting here is "the compensation for your oaths when you swear." which is stated in this passage after the fasting is mentioned. So whereas God does consider a month of daily fasting to be equal to feeding 30 people, this fasting for 3 days is not a compensation, and therefore not equal to the feeding of 10 people mentioned before but only to the breaking of one's oath as the passage clearly states. All other passages keep in line with this 1 to 1 relationship and have no such clauses. Because of this clause it would be wise to say that God put this clause here for a reason. Considering the possiblity that one action may have completely different worth when treated as a remedy to different distinct actions, and that actions can't always be measured as numbers are, makes this clause sit better with me. Afterall, it is through having a better understanding of reality (God's works) that the Quran will make more sense to us.
A month, or shahr in Arabic can be 29 or 30 days but the Quran prefers 30 according to the 1/1 relationship implied in its verses where there aren't any clauses to indicate otherwise. There are also only 12 months in a year. Per 9:36 literally from the Arabic 'The count of months is to be twelve.' 'iddata ash-shuhoori 'indallahi ithna 'ashara shahran. Now when we get here some people start having trouble. They know that an accurate year from solstice to solstice is 365 days and that 12 months consisting of 30 days is only 360 days. Although this seems like a problem this is not really a problem. Now, we need to think out of the box, because nature, and especially God doesn't always fit into a box. The problem is that people love for nature to fit into their already pre-concieved ways of thinking. If the Quran says that there are 12 months in a year and each month is 30 days then there are 12 months in a year even if there are 365 days in a year. Adding a 13 month would go against God's commands mentioned in 9:37 which forbids adding a month, and allowing any number of months that God has forbidden.
When you count the months as 30 days you end up with 5 extra days but those 5 extra days don't equal a month. So there are 12 months in a year . . . and 5 days. Some people don't like that these 5 days are just kind of out there, and not part of a month. That is why the Western Calendars made some months 31 days. To some this even smells of imperfection, and as we know God is far from imperfect. They would say that if God said twelve months, then a year has to exactly equal 12 months. To those who are not satisfied with the un-evenness of this 12, 30-day month year, if there is nothing innately wrong with it then why can't you accept it? God and His creation are always perfect even if they don't fit into our narrow concept of perfection. We have to mold our minds to understand reality in is real workings, only then can we capitilize on it and benefit from it.
However to put this in mathematical terms for those who can only understand this in a mathematical way, when counting in units there is no need to count fractions because they are not units. Once you define a month as a unit and 12 of these units fits into a year it doesn't matter if there is room that equals a fraction of that same unit, because you were counting in units only. That is not to say that we need to ignore the 5 days, they are obviously there but we are not looking at them as a month and that is what is important. If you look a little closer there is a perfection in this system, because even though these 5 days aren't apart of a month, each month is divided up into six, 5 day weeks and this extra week offers a perfect transition into the new year. That is, a week of the year's passing, and then the new year starts. You don't have to play around with the calendar or do anything to it. So here is preciseness where none was thought to be. A precise 73 weeks in the year. It has been people's need to try to impose their own concept of precision onto nature which is why scientist even to this day have to add a day and take a day a way every so often to the western Modern Gegorian calendar. All that for nothing.
The Quran doesn't say we have to follow 7 day weeks. That was something the ancients did to try to make the earthly world reflect the Grander scheme, in particularly the time God used to make the world, according to the Bible. And it is a tradition that our cultures have followed. But this is irrelevant to us. Mainly because considering Classical Arabic, days can also mean eras and could be thousands or thousands of thousands of thousands (billions) of years. The Quran shows us this by pointing out the duration of certain actions as days that equal thousands of years in our reckoning. It is my opinion that the Universe wasn't created in 7 days or eras and then it was finished. It was set within the span of 7 eras. God is still creating out there, and here. So the Universe has 7 eras and when those seven eras are finished God will assume the throne (Thy kingdom come). There are no dissenters in a kingship/kingdom, so even though God is king of kings He has not assumed the throne yet and put everyone in their place as long as he is letting us run a muck on His earth. But we know that that is for a reason as well. In particular, to give us a chance for redemption and to reclaim the glory He gave us in the beginning by doing His bidding while we're here. The day when He puts everyone in their place will be on the day of dues, the day of judgement.
It is taken as a fact that there are 53 weeks in a Gregorian/Modern year but if you divide 365 by 7 you get 52.142 . . etc. God gave us something simple and precise here, we need to follow it, instead of trying to force our bogus ideas onto nature and the Quran.
Muslims, and especially Arab Muslims, have continued to follow in the traditions of their Jewish forefathers who had a luni-solar calendar and who reckoned the months by the appearence of the moon's waxing crescent. Because of the historical avoidance of Quranic scrutiny they never saw the answer in the Quran on how they could fix the innaccuracy of the calendar when they went ahead and started following the obvious suggestion of the Quran to not count 13 months in a year, which is what the Jews were doing. Furthermore because they prefered to view Ramadan in line with the Arab traditions of time-keeping instead of seeing it for its inherent Arabic meaning which the early Arabs also understood, and because of the ethno-centric tendencies and preferences of these people they decided to keep in line with their tribal traditions of pilgrimage and not even consider, let alone embrace, the grander one promoted in the Quran. They myopically pidgeonholed these words, pilgrimage and Ramadan, in a way that has caused the contradictions and confusions with the Islamic calendar that are just commonly ignored instead of seriously confronted and dealt with.
And what about the crescent moons or moon phases mention in 2:189. Well this word is ahillat is in Classical Arabic. It is a plural word that can find its singular in haleel or hilaal, early Arabs had they thought on this would have recognized this. Hilaal means crescent moon. However, since we know that the Islamic calendar is not accurate and can in no way offer us a stable time system that existed during the time of the Quran- Which means that it is usesless even in being able to indicate the Pre-Islamic Ramadan that Muhammad was given the Quran in-, and since we know that the Pre-Islamic calendar, based on crescent moons, cannot stay accurate without adding a 13 month, there is no reason for us to see the word ahillat in 2:189 and take it as the plural of hilaal, or crescent moon. We should rather take it as the haleel of 5:3. 5:3 says not to eat things 'uhilla' in a name other than God's. Uhilla is the passive of ahalla (a 4th form Arabic verb) which can mean to 'to consecrate' or 'to proclaim.' It also means 'to cut/to cut through' in the context where a blade is involved. Slaughtering of animals for food can give this context. Based on the relationships between Arabic forms, the passive 4th and 2nd forms can equal the first form and be directly related back to the form fa'eel which equals would be haleel. That means that maa uhilla = haleel just as maa uslima = saleem (what is made safe = safe) only when the 4th form is causative. So haleel= a consecration. Ahillat can be the plural of haleel. Ahillat can also be the plural of hallun, and haleel can equal haleel, both being verbal nouns. Hall also has a meaning of to rejoice, with a context of open and vociferous rejoicing.
The whole passage of 2:189 is speaking about pilgrimage, and al-ahillat can be refering to the slaughtering of animals to feed the pilgrims and the poor, or the open rejoicing to take place, referred to in 2:200. These consecrations and rejoicing being mawaaqeet(usually translated as 'timings' from the singular meeqaat). However this can refer to them being timed (from the singular mawqoot) and not at random for the people making pilgrimage.
lastly there is a possiblity that this relates the the periods of waxing and waning moons. Which are approximinately the first 10 days of a lunar period and the last 10 days. These could be the days of each of the 4 months that the believers are supposed to come together and celebrate God praises and hold other activities (al-'umrah).
All in all, there is no need to follow the Islamic calendar or the pre-Islamic calendar for that matter, as both of them are not calendars based on the time keeping principles that we are taught within the Quran. The daylight is to serve as a sign for us when it comes to reckoning the years, and more specifically the solstices. The months are 12, there is an extra 5 days on the tail of these 12 month, and the units of these 12 months upon further examination would logically be six, 5 day weeks. 17:12 below seems to intimate that the summer soslstices are to represent counts of the new years. This seems to imply that the southern hemisphere would have a different new year than the northern hemisphere. In truth there are 4 solid earth years, each corresonding to the rotational period of each equinox of the 4 equinoxes. It is interesting to note that the new year for the traditional Islamic year was not decided by our last prophet but after he had passed, having nothing to do with our last prophet, nothing to do with the Quran and nothing to do with earthly time.
17:12 "We have established the night and daylight as two symbols. We erase away from the wonder of night and fill it in with the wonder of the light of day so you can seek to benefit from your Sustainer's grace and know the count of years through calculation, and through everything that we would make clear."
10:5 "It is God who has made the sun a shining radiance. The moon, as a light, He has measured out into phases. Learn the count of the years, through calculation, consideration and estimation, equally. God has created these things as valid and sound. They make wonders plain and clear for those who are informed."