Ramadan, the most important month of the year in the Muslim calendar, begins Sunday. For the next 30 days, Muslims around the world will abstain from eating or drinking during daylight hours.

Here’s everything you need to know about why Muslims celebrate, how to wish someone a happy Ramadan and what happens at the end of the month.

What is Ramadan?

For Muslims, the monthlong celebration commemorates Allah, the Arabic name for God, giving the first verses of the Quran, the Muslim holy book, to the Prophet Muhammad in the year 610 A.D.

For 30 days, Muslims around the world do not eat from dawn to dusk, pray intensely and gather for nightly feasts to break the fast.

Observing Ramadan is one of the Five Pillars of Islam, the five duties that are obligatory for every Muslim.

When is Ramadan in 2019?

The date of Ramadan varies each year and is determined by the cycles of the moon. Ramadan is the ninth month of the lunar Islamic calendar, and it officially begins the morning after the crescent moon is visible to the naked eye.

But since the moon’s visibility in different parts of the world varies based on weather and geography, in many areas, Ramadan does not officially start until religious leaders declare they’ve seen the crescent moon.

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In 2019, Ramadan will begin at sunset on Sunday, May 5 and last through sundown on Tuesday, June 4. In 2020, it will begin April 23, and in 2021, April 12.

Do you say ‘Happy Ramadan?’

Yes, a non-Muslim may wish someone a "Happy Ramadan." But Muslims typically don't say that to each other. The Arabic greeting is "Ramadan Mubarak," which means "Happy Ramadan," or "Have a blessed Ramadan." Another is "Ramadan Kareem," which means "Have a generous Ramadan."

Why do Muslims fast?

Ramadan is a month of spiritual dedication and personal growth. It is intended to strengthen Muslims’ relationship with God.

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Muslims around the world give up earthly pleasures, focus on prayer and read the Quran. Many also donate to charities and hunger relief efforts.

When do Muslims fast?

Muslims fast from sunrise, known as suhoor, to sunset, known as iftar.

Observers eat a pre-dawn meal before sunrise (common foods include energy-dense dates, mashed fava beans or potatoes) and another after sunset (typically a feast with family and friends).

What can Muslims eat or drink?

Nothing during daylight hours. According to the Islamic Association of Raleigh, taking one sip of water invalidates the day’s fast, which must then be made up at a later date. However, eating or drinking because of forgetfulness or coercion are exceptions, and the person's fast remains valid.

Muslims can shower, apply eye drops, take injections or brush their teeth during daylight hours as long as nothing is swallowed.

How do Muslims break the fast?

Muslims typically sip water and eat dates before performing sunset prayers. They then share an “iftar” feast with friends and family. Many mosques host free iftar meals for the public during Ramadan.

Does every Muslim have to fast?

Yes, with some exceptions. Children under 13 who haven’t yet reached puberty, women who are menstruating, sick people, elderly people, pregnant women, breast-feeding mothers and travelers are exempt.

Can you smoke cigarettes or vape during Ramadan?

Ramadan is not only about fasting from food and drink, but also abstaining from other types of pleasures, including sex, swearing and arguing. Many Muslims give up smoking and drinking alcohol as a means of spiritual purification during the month.

Can you kiss during Ramadan?

Yes. According to the Islamic Association of Raleigh, it is acceptable for spouses to kiss during Ramadan “as long as one is able to control oneself.”

What about working out during Ramadan?

Many Muslims who choose to exercise during Ramadan do so right before sunset, just before breaking the day’s fast. Mid-day workouts are uncommon due to not being able to eat or drink during daylight hours.

Professional athletes who travel aren’t required to fast, but some, such as professional soccer player Mohamed El-Munir of Major League Soccer’s Los Angeles Football Club, choose to do so.

What happens at the end of Ramadan?

The month concludes with a three-day celebration known as Eid al-Fitr, or the Festival of the Breaking of the Fast. Gifts are exchanged, and children often receive cash and new clothing. One Muslim writer likens it to “the Muslim version of Christmas.”

Follow Sarah Bahr on Twitter: @smbahr14