“Kapan ya hari raya 1433H?” tanyaku dalam hati. Kalau menurut kalender Hijra sepatutnya jatuh pad hari Minggu tanggal 19 Agustus. Tapi kenapa 1 Syawal yang merupakan bulan baru tidak sesuai dengan phasa-phasa bulan yang saya lihat di website ini? Padahal menurut website tersebut, 1 Ramadhan bersesuaian dengan terjadinya bulan baru pada tanggal 20 Juli 2012 seperti yang ditunjukkan pada gambar (a). Sedangkan 1 Syawal yang seharusnya jatuh pada tanggal 18 Agustus 2012 (b), malah jatuh pada tanggal 19 Agustus 2012.
Memahami penjelasan lengkap di http://www.hijracalendar.com/
The Islamic calendar (Hijra calendar) is a purely lunar calendar. It contains 12 months that are based on the phases and stages of the moon, and because 12 synodic months is only 12 x 29.53059=354.3671 days, the Islamic calendar is consistently shorter than a tropical year, and therefore it shifts with respect to the Christian calendar. The calendar is based on the Qur’an (Sura IX, 36-37) and its proper observance is a sacred duty for Muslims.
Unfortunately some Muslim astronomers have suggested that lunar date lines should be marked on the world map for the Muslims to begin their fasting and celebrating their Eid. According to them this would depend on the first visibility of the crescent and the date would begin form that place. The so-called curved lunar date lines always keep on changing and they pass through cities, towns and even houses! They do not abide the rules of the date line. So the Lunar date lines are impractical and meaningless. They are neither scientific nor Islamic.
Hijra Calendar is the same astronomical Lunar Calendar and the month begins and ends on conjunction (Astronomical new moon), conjunction being the last day of the month. Sometimes the conjunction falls on 29th day and sometimes on 30th day. Each phase of the moon and its angular distance indicates each date and it is like a natural calendar hung in the sky. Sometimes 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. Its physical visibility is not the criterion. The astronomical new moon times and dates are already computed exactly for thousands of years backward and forward.
Software untuk memahami pergerakan bulan http://www.stellarium.org/