Hundreds of thousands of Muslims live in Texas. According to the World Population Review, there are more than 300,000 Muslims in Texas.

Muslims in Texas, like millions of Muslims around the world, have begun observing Ramadan, a month of fasting, spirituality and reflection.

This holiday is celebrated on a different date every year. Because the Islamic calendar follows lunar cycles, Ramadan begins approximately 11 days earlier each year than in the Gregorian calendar. The exact date is determined by observing the new moon. The first day of Ramadan in Mecca this year was February 18th.

Fasting can last for 29 or 30 days, depending on when the moon appears, marking the beginning of the next month.

Here’s what you need to know about Islamic holidays.

According to Al JazeeraRamadan is determined by the Islamic lunar calendar (also known as the Hijri calendar), which is based on the phases of the moon. Here’s how Ramadan is determined:

• The Islamic calendar consists of 12 lunar months, each lasting between 29 and 30 days, depending on the moon’s appearance.
• The beginning of Ramadan is marked by the appearance of a new moon (Hilal). This observation can be made with the naked eye or by astronomical calculations.
• The sightings usually involve religious authorities or committees who announce the start of Ramadan based on the appearance of the moon.

Muslims believe that Ramadan is the month in which the first verses of the Quran were revealed to the Prophet Muhammad more than 1,400 years ago. During this holy month, Muslims refrain from eating, drinking, smoking, and sexual relations from just before the sunrise prayer, Fajr, to the sunset prayer, Maghrib.

The purpose of fasting is to develop taqwa, or awareness of God.

Fasting is one of the five pillars of Islam, along with declaration of faith, daily prayer, charity, and, if physically and financially able, participating in the Hajj pilgrimage to Mecca.

Muslims who have reached puberty and are physically fit fast from sunrise to sunset. Fasting not only means abstaining from food and drink, but also abstaining from sexual relations and misconduct. Those who are sick or on a journey are exempt from the fast.

“The purpose is to develop a sense of God, which is taqwa in Arabic,” Imam Ebad Rahman, religious life associate for Islamic life at Columbia University, told USA TODAY.

During Ramadan, Muslims are encouraged to learn more about the teachings of the Quran, and some even take on the challenge of reading the religious text in its entirety.

The last 10 nights of Ramadan are considered especially sacred, with the holiest nights being Laylat al-Qadrit happened that night.

It is not known exactly when Laylat al-Qadr, known as the “Night of Power,” will occur, but many believe it is likely to fall on one of the last ten odd nights of Ramadan. It is believed that good deeds increase significantly on that night, and Muslims may also spend the night in reflection, prayer, and other acts of worship.

According to MuslimMade.org, the holy day ends on March 30th.

Eid al-Fitr is a religious holiday that marks the end of Ramadan. Muslims celebrate the special day by listening to special prayers and sermons on Eid morning. As part of the tradition, parents, relatives and friends give young children various gifts such as new clothes and money. It is expected to be held on or before April 9th.