Ramadan to Begin Tonight, Probably At sundown tonight, Muslims the world over will welcome Ramadan, the holiest month in the Islamic calendar. The ninth month of Islam's lunar calendar, Ramadan is believed to be the month in which the Quran was revealed. During Ramadan, which begins with the new crescent moon, observant Muslims refrain from food, water and sexual relations between dawn and dusk. Exactly when the holy month begins, however, is a matter of annual debate. Ramadan technically begins only when Islamic authorities in each country announce that the new crescent moon has been seen. Despite astronomers' ability to accurately predict when the moon will appear, most Islamic scholars insist that confirmed reports of actual sightings are necessary in order to declare the beginning of Ramadan. Adding to the confusion is the emergence of CCD-camera techniques that can render an image of the moon in broad daylight, Nidhal Guessoum, an astronomer at American University of Sharjah, in the United Arab Emirates, wrote in a column for the Huffington Post. "This has further complicated the already complex relationship between Muslim astronomers and modernists on one side and the traditional Muslim scholars ('ulamas') on the other," Guessoum wrote. In the past several years, mobile app developers have tapped a growing market among Ramadan observers. Some apps calculate sunrise and sunset times at any location, while others notify users of prayer times. During Ramadan, Muslims are encouraged to engage in spiritual reflection and worship and to practice self-discipline through the resistance of temptation. Muslims are encouraged to pray more frequently and read the entire Quran before the holiday of Eid ul-Fitr marks the end of Ramadan. This year, Eid ul-Fitr will arrive on the evening of Aug. 17.