Hijri Committee of India (HCI) has been engaged in researching and propagating an Islamic Lunar Calendar, to be applied universally for the whole mankind, for the last 4 decades. During the last 19 years it has published true Hijri Calendar which has dates exactly tallying with the phases of moon, as directed in Noble Qur’an 2:189.
The Islamic calendar (or Hijri calendar) is a purely lunar calendar. It is the same astronomical Lunar Calendar and the month begins and ends on the conjunction day ( Astronomical new moon), means conjunction is last day of the month. Some time it is on 29th day and some times 30th day. The calendar contains 12 months that are based on the Qur’an (Sura IX, 36-37). It is based on the motion of the Moon and its proper observance is a sacred duty for Muslims. Each phase of moon and its angular distance is indicate each Date as shown a natural calendar hung in the sky. Some times we cannot see the moon because of the changes in weather. but it does not make any difference in calendar dates because it is related to the motion of the moon. Not its physical visibility. The astronomical new moon time and date already computed exactly for thousands of years backward and forward.