Rules of dating in islam
An Islamic year consistently falls about 11 days short of the solar year.
For that reason, the Islamic calendar cannot be used for agriculture or other activities traditionally linked to the seasons, and most Muslim countries officially use the Gregorian calendar as their civil calendar alongside the Hijri system. The traditional version of the Islamic calendar requires an authorized person or committee to make an actual sighting of the Crescent Moon to determine the length of each month.
For example, January 1, 2016 fell into year 1437 AH in the Lunar Hijri calendar, which corresponds to year 1394 in the Solar Hijri calendar.
Even though the Islamic calendar year does not match up with the length of a solar year, it does not feature a correction mechanism like leap days in the Gregorian calendar to make up for the deviation.
Each month lasts for a full lunation, which is the time span from one New Moon to the next.
This Moon cycle encompasses all the phases of the Moon.
If the Crescent Moon is visible shortly after sunset on the evening of day 29, the following day is the first day of the new month.The fact that goodness CAN exist, is proof that Allah swt DOES exist.