When that happens, the moon only just becomes visible at the beginning of the first month in the sequence, and just fails to do so on the 29 th of the fourth month. The effects of changing geographic and lunar longitude and latitude The Islamic world does not have a uniform policy regarding the acceptance of crescent sightings from other countries when deciding whether or not to declare the onset of a new month. Many authorities will consider only observations made from within their own national boundary. At least once in the past, however, evidence from the Yemen has been cited for the commencement of Ramadan in the United Arab Emirates. Furthermore, many Ihna asheri Shi ites are happy to abide by reports made even in another continent provided they can receive such evidence before their own dawn next morning.
Crescent spotting at dusk tends to become easier as one moves westwards.
In fact, in northwest Africa the sun sets approximately eight hours after it does in southeast Asia, and during that interval a New Moon moves an extra four degrees away from the sun which could make all the difference between a successful sighting and a failure. Often, a newborn crescent will be much more obvious in the opposite hemisphere, because of seasonal variations in the angle between the ecliptic and the horizon at dusk. In the Northern Hemisphere, this angle is at its steepest during March, thereby maximising the altitude of the New Moon just after sunset. However, in the Southern Hemisphere, that angle is shallowest in March. Six months later, those relationships are reversed.