[tz] Calculating dates of Ramadan

David Patte dpatte at relativedata.com
Wed May 16 11:57:23 UTC 2012

Different countries calculate a 'secular' start of Islamic month 
differently than others. I am aware for example that the astronomical 
rules used to calculate this 'secular' stat of month are different in 
Egypt, than in Saudi Arabia or Pakistan. But the Imams have the right to 
declare the religious start of month whenever they deem fit, which in 
the case of some countries could be before the their 'secular' calculation.

On 2012-05-16 6:29, Ian Abbott wrote:
> On 2012-05-16 10:28, Tim Thornton wrote:
>> Regarding calculating Ramadan:
>> The Islamic calendar is lunar, not solar, and is about 11 or 12 days 
>> shorter
>> than the "normal" Gregorian calendar.
>> Months (including Ramadan) start when the first crescent of a new 
>> moon is
>> sighted. This varies according to the atmospheric conditions and the 
>> exact
>> positions of earth, sun and moon, but can be calculated to within 
>> about a
>> day for any given location, which is good enough for tz data in the 
>> absence
>> of any further specific information for a location.
>> There is also an ongoing debate in Islam on whether the calculated 
>> date is
>> good enough, or whether they should stick with past practice of having
>> official observers watching the sky to announce the start of the month.
>> What cannot be done is to say that it always falls between a given 
>> pair of
>> Gregorian calendar dates, due to its shifting.
>> Tim
> In practice, how much does the observed (as in astronomical) date 
> differ from the calculated date?  Does it ever start _before_ the 
> calculated date?


More information about the tz mailing list