Suchergebnisse

The sunrise, sunset, and day length times for Baghdad (Latitude =33.34º N, Longitude =44.43º E) were calculated with high accuracy on a daily basis during 2019. The results showed that the earliest time of sunrise in Baghdad was at 4h: 53m from 5 Jun. to 20 Jun while the latest was at 7h: 07m from 5 Jan. to 11 Jan. The earliest time of sunset in Baghdad was at16 h: 55m from 30 Nov. to 10 Dec. whereas the latest was at 19h: 16m from 25 Jun. to 5 Jul. The minimum period of day length in Baghdad was 9h: 57m) in 17 Dec. whereas the maximum period was 14h: 22m) in 20 Jun. Day length was calculated and compared among regions of different latitudes(0, 15, 30, 45 and 60 north).

Predicting the visibility of the lunar crescent drew great attention during the Middle Ages, especially among Muslims, because the dates of religious practices in Islam and calendars, in addition to being aware of the motion of the moon in its orbit, are based on the lunar month.
This paper aims to study the development of crescent visibility criteria from ancient times through the medieval period to the modern update. Some basics and astronomical terms related to crescent visibility are presented and then a comprehensive view of crescent visibility criteria is examined by surveying about 54 published research papers related to the issue of crescent visibility. Each research paper is summarized, classified, and the results evaluated. Also, the previous studies are divided into two parts, including the ancient and medieval ages, which depend on the visual observations of the naked eye. We found that predicting the crescent's visibility started at the end of the Islamic era. The second part shows that at the beginning of the twentieth century, engineering criteria were introduced into research for the prediction of crescent visibility, then physical engineering criteria, weather conditions, and observer location on the Earth's surface were introduced. Currently, modern technologies have been introduced, such as CCD cameras and image processing technology. The study concludes that there are no 100% accurate criteria that correspond to the truth and completely match the observations, as these criteria need improvements by increasing the number of observations and introducing modern technologies to the crescent's visibility prediction.

The entry time of the prayer in Islam is a prerequisite condition for performing obligatory prayers, and prayer times to be performed in Islam coincides with the time changes of the position of the sun. The elliptical and equatorial coordinates of the sun were calculated for different latitudes. The prayer times for the city of Baghdad were calculated at (latitude = 33.34º N, longitude = 44.43 E) with high accuracy for the year 2021 AD. The results showed that all prayer times are affected by latitude according to each region except (Dhuhr prayer (, it changes with the change of the equation of time, because the equation of time does not depend on latitude, but rather on the sun's declination, which depends on date. We also made improvements to the accuracy of calculating prayer times, where the disappearance of evening twilight (Isha prayer) was calculated when the sun was below the western horizon at an angle of (170 ) and for )Fajr prayer( at an angle of (180) below the eastern horizon. Minutes were added to enable entering the time for )Dhuhr prayer( (5 minutes) and )Asr prayer( (3 minutes).
The results show that the shadow of the meridian varies every day of the year from one point to another on the surface of the globe, so it is non-existent if the sun is perpendicular to the earth at the time of the meridian, and it has a specific length if the latitude of the place exceeds the value (23.50) the Tropic of Cancer or the Tropic of Capricorn), and its length increases as we move towards higher latitudes.
In addition, the results of our program were compared with the program of the Islamic project for all prayer times for the cities of Baghdad and Mosul for one year, and it showed a good match for the results, with a difference in some times and days of no more than one minute due to the modifications we added to calculate the effect of altitude above sea level. Practical observation was also conducted to check the times of the Dhuhr, Asr and Maghrib prayers for several days during the year 2021 AD, and the results were identical with our theoretical results.