The Possible Range Arc of Vision for Aphelion and Perihelion Group of Hilal Visibility

摘要

Unique and reliable criteria on Hilal visibility is important for determine the beginning of new month in Islamic Calendar. One of possible criteria on Hilal Visibility is Arc of Vision (ARCV). ARCV is defined the different between the altitude of the moon and the sun at the time of sunset. We present our preliminary study possible criteria on Hilal visibility for Aphelion Groups (AG), is defined all Hilal member of Islamic Lunation Variant Number (ILVn) 223, 186 and 087 and Perihelion Groups (PG), is defined all Hilal member of Islamic Lunation Variant Number (ILVn) 217, 155 and 019. We find some ranges of ARCV as follows: (1) Aphelion Groups (AG): ILVn 223:7°.82 < ARCV < 10°.87, ILVn 186:7°.82 < ARCV < 10°.52 and ILVn 087:7°.86 < ARCV < 10°.86. (2) Perihelion Groups (PG): ILVn 217:7°.73 < ARCV < 10°.71, ILVn 155:7°.68 < ARCV < 10°.18 and ILVn 019:7°.79 < ARCV < 10°.82. Those Hilal, in the ARCV range are composed of first lunar crescent visibility after conjunction with fraction of illumination of 1% up to as thin as 0.5%.