For Muslims adhering to scientific lunar calculations, Ramadan will begin tomorrow.
But for other practicing Muslims, Ramadan will start after the new moon has been sighted -- either by members of their local mosque or by others around the world. Many Muslims will look for the new moon Wednesday night.
If it is spotted, fasting will begin Thursday. If not, fasting will begin Friday.
Moon sighting is the traditional way of determining when to begin Ramadan, according to Habeeb Ahmed, a leader of the Islamic Center of Long Island in Westbury, one of Long Island's largest mosques.
"Now, with the advancement of science, many people, for example my mosque, have decided to go by the calculation," Ahmed said.
The holy month is observed by many of the world's estimated 1.6 billion Muslims, including about 75,000 on Long Island.
The Islamic Center of Long Island follows the calculations determined by the Fiqh Council of North America, which is composed of scholars and scientists, Ahmed said.
Dr. Hafiz Rehman, a leader at the Muslim Center of Long Island in Bay Shore, said some people follow local moon sightings while others follow international moon sightings.
"Both of these schools of thought are OK," he said.
While determining when to begin Ramadan is an individual decision, most people follow the mosque they attend, Ahmed said.
Ramadan is one of the five pillars of Islam. It commemorates the time when the prophet Muhammad received the Quran, the holiest book in Islam, from the angel Gabriel in the year 610.
During Ramadan, Muslims go to bed around midnight, after the last prayer of the day, and rise at about 3 a.m. so they can have a light breakfast before dawn and say the first prayer of the new day.
From sunrise until sunset, they cannot eat or drink any liquids, including water. After sunset, they break the fast with a festive meal, often in a mosque or at home, or sometimes with friends.
Each evening, Muslims spend about an hour and a half at a mosque listening to someone who has memorized the Quran recite one chapter from the holy book.
During Ramadan, Muslims are asked to give to charity and be mindful of their maker, Ahmed said.
Fasting teaches patience and an understanding of those who don't have food or proper drinking water.
"We are very fortunate that we live in a western country here," said Ahmed, 60, of Albertson, explaining that many on Long Island have air-conditioned homes, cars and offices. In parts of Africa and India, temperatures can be sweltering.
During Ramadan, Muslims must not look at, listen to, or utter anything bad, said Rehman, 68. "It's not just a fast of the tummy," he said.
Nayyar Imam, 59, of Mount Sinai, the president of the Long Island Muslim Alliance, said he usually becomes accustomed to fasting within three days. To distract himself, he works or reads the Quran. Drinking a cup of coffee before sunrise helps him to power through the day.
"It's not really that bad," he said. "The human body is so adaptable."