I am writing this after reading about the Muslim fasting month. The start of the month depends on the sighting of the moon. But this date is never the same. It always changes. It may be the 7th or 10th or even the 3rd of the next english month.

My question is Why? Why does this change? Why does the lunar calender change? Its not like the moon slows down or something. So what is it?

In: Other

One lunar cycle takes 27.3 days. This doesn’t match up with our 30/31/28/29 days per month.

Lunar calendars don’t sync up with the Gregorian calendar, as 12 lunar cycles ends up being 11 days short of a sidereal (365.25 day) year.

Consider, why was May 1st this year a Wednesday, but June 1st will be a Saturday?

Because a week has 7 days, and May has 31, and 7 doesn’t evenly divide 31. So, may has 4 full weeks in it, and then 3 more days left over. So the next month starts on a different day of the week.

It’s the same basic idea with the lunar calendar and solar calendar. The length of the month doesn’t evenly divide the length of the year, so dates shift over time.

Imagine if your week has 7 days, Mon, Tues, Wed, Thurs… And imagine I follow a 5 day week, let’s call them day 1-5

So let’s “start” the weeks on their first day so it’s 1 for me and Monday for you, the next day is my day 2 and your Tuesday…. The day 5 is your Friday. But wait after that day, it loops back to my day 1, but that’s your Saturday… My new week is 2 days “behind yours”. Now imagine this but for something with differing year lengths.

Because our calendar is man made and based on the earth’s rotation around the sun. The moon doesn’t abide by these rules and has its own ‘calendar’. You could just as well live by a calendar based on the movement of the moon, however the modern calendar has just been widely accepted as a better option.