Substitles available in: English, Arabic, Turkish*, and French.
*Turkish subtitles provided by Azesra.

Metonic Cycle:
Ancient mathematicians realized that if they wanted to keep the solar and lunar dates in line, the shortest possible cycle would take 19 years.

How many leap years would we have in this 19-year-cycle?
• 19 solar years are approximately 6939.75 days (= 19 years x 365.25 days)
• 19 years made of 12 lunar months are approximately 6732.84 days (= 19 years x 12 months x 29.53 days)
• Missing (leap) days: 19 "solar years" - 19 "years made of 12 lunar months" =
6939.75 days - 6732.84 days = 206.91 days.
So, after a period of 19 years, the lunair calendar is missing 207 days. (Which means that we must add 207 days thoughout the 19 years, in order to place the months back within their respective seasons).
How will we add these 207 days without messing up the cycle of moon phases and the seasonal cycle? The best way to do this is by adding these missing days in the form of leap months.
• Converting days to months: (206.91 days)/29.53 days = 7.007 months
So, approximately 7 leap months must be added to compensate for the missing days. This means that during a period of 19 years, 7 will be leap years (containing 13 months each) and 12 will be regular years (containing 12 months each).
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Many people believe that the Islamic Calendar is lunar. Yet, upon closer examination of the meanings of the Islamic months, it becomes clear that most of them define distinct seasonal events. Why is it the case, when the calendar is supposed to be lunar (and thus cannot keep track of seasons)?
Is it possible that the Islamic Calendar is a solar one? Well, this is unlikely because solar calendars cannot keep track of the moon phases, while Quran 2:189 mentions their importance for time-keeping.
So then, which one is it?
This video gives a detailed explanation of what the true Islamic Calendar is and presents evidence from the Holy Quran.
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Video clip of moon rotating around earth:
Turtlediary. “Phases of the Moon | Science Video for Kids.” YouTube video, length: 3:52. April 6, 2016.    • 7 Moon Phases Explained! How does the...  . Part of this work (from 0:55 to 0:59 in the original video) was reproduced for nonprofit educational purposes.
- Video clip of earth rotating around sun:
Turtlediary. “Science Video for Kids: Earth's Revolution & Rotation.” YouTube video, length: 8:15. March 11, 2016.    • Earth's Rotation & Orbit *Why Is a Ye...  . Part of this work (from 1:04 to 1:15 in the original video) was reproduced for nonprofit educational purposes.
- Video clip of moon orbiting earth and earth orbiting sun:
Turtlediary. “Phases of the Moon | Science Video for Kids.” YouTube video, length: 3:52. April 6, 2016.    • 7 Moon Phases Explained! How does the...  . Part of this work (from 0:48 to 0:54 in the original video) was reproduced for nonprofit educational purposes.