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Is there a mistake in the calendar?

Posted 10 years ago
Hello Wolfram Community,
I have question about the converted date. I wanted to look up wich date we have according to the islamic calendar, but unfortunately the rest of the web is 1 day infront of Wolfram Alpha. All the time I trusted Wolfram Alpha, and I'm not going to chance that attitude, but this time it seems wrong. Is there a wrong information in the database or is all the other sites wrong?

Thanks a lot
best regards
Lotfy
POSTED BY: Lotfy Yildiz
4 Replies
Posted 10 years ago
Is there the posibility that Wolfram Alpha gives the date at 12:00 o'clock and the other sites the date after sunset (so the times in which the date changes are different) ? This would explain the one day shift, and also why there are two different dates. So both would be right somehow.
Actually I don't know much about this subject either, I just want to understand it.

After checking for Ramadan:
ramadan 1 1435 to gregorian date
Wolfram Alpha showed me June 29, while
http://en.wikipedia.org/wiki/Ramadan_%28calendar_month%29#Timing
shows me June 28. (I asume that wikipedia is reliable, because other sites without a calculater give the same date)

So I think it might have to do something with the sunset.Also Wolfram Alpha writes "until sunset"

Thank you for your responses and your time.
best regards
Lotfy

edit: i had to delete some sentences because I mixed something up.
POSTED BY: Lotfy Yildiz
Thanks for the example.  I note that on the site you quote it says "*There is a small probability of one day error."  And a number of other sites have the same advisory (perhaps they are all using the same copied javascript algorithm behind the scenes).  And testing some of the sites one can put in invalid dates and still get an answer (e.g. April 31st which does not exist).  Mathematica of coruse sensibly gives an error message if you try to convert April 31.

In Mathematica (which presumably is the code behind the Wolfram|Alpha calculation) one gets
In[2]:= Needs["Calendar`"]

In[53]:= CalendarChange[{2014, 4, 30}, Gregorian, Islamic]

Out[3]= {1435, 6, 29}

And it seems that this is probably the correct answer.  Note that other sites agree with this.  For example 

http://www.iacad.gov.ae/en/pages/hijritogregorian.aspx

and 

http://www.mela.us/committees/hegira.html

But the code behind these sites is only as good as what one sees (i.e., one needs to look at the Javascript source behind, for example, the last pate's link... easy enough to see if one "shows source" for the page).

here's the wikipedia article:

http://en.wikipedia.org/wiki/Islamic_calendar#Converting_Hijri_to_Gregorian_date_or_vice_versa

I actually don't know much about this subject, so take my links & c with grains of salt. 
POSTED BY: David Reiss
Posted 10 years ago
sorry, I'll try:
input:
tomorrow in islamic calendar
or
April 30 2014 to islamic calendar
output: 29 Jumada,
other source: http://www.islamicfinder.org/dateConversion.php?mode=ger-hij&day=30&month=4&year=2014&date_result=1
output: 01 Rajab (is one day after 29 Jumada)
POSTED BY: Lotfy Yildiz
As always, giving an example would help us folks who'd like to examine the problem and offer help...  ;-)
POSTED BY: David Reiss
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