ANALYSIS OF OBSERVATIONS OF EARLIEST VISIBILITY OF THE LUNAR CRESCENT

摘要

Predicting the visibility of thin lunar-crescents following the new moon is difficult and challenging for several technical reasons. The visibility of the earliest new moon has long been used to determine the lunar-crescent calendar and is still used today. Many criteria exist for the first visibility of the lunar crescent. Here, we test the most-commonly-used criteria for thin-lunar-crescent visibility. We used 545 observations, including both positive and negative sightings, made by professional and highly-trained astronomers over a duration of 27 years (1988 2015) and from different locations at latitudes between 20 degrees N and 29 degrees N (within Saudi Arabia). We developed a new criterion for lunar-crescent visibility using lunar-crescent width (W) and the arc of vision (ARCV). This new model can be used to predict the visibility of the lunar crescent by naked eye or aided eye, which is fundamental for the lunar-crescent calendar followed by several cultures and religions.