WATCH THE SKY: Why the crescent moon determines the start of Ramadan

By the time Ramadan arrives yearly, Muslims all around the world enter a month defined by fasting, prayer, and spiritual renewal. Yet, before the first day of fasting begins, the start of the month depends on something far quieter — the appearance of a thin crescent in the sky.

For decades, Ramadan has not been marked by a fixed calendar date but by the sighting of the new moon.

A fresh start

It is considered as one of the holiest months of the year for Muslims.

Ramadan is significant as it is believed that during this month the Qur’an and its first verses were revealed to the Prophet Muhammad. During this month, Muslims fast from food and drink during the sunlit hours as their way of drawing closer to God and cultivating self-control, gratitude, and compassion for those less fortunate.

Fasting during Ramadan is not simply about abstaining from food but also following a spiritual program that includes:

• Physical discipline
• Increased prayer
• Qur’an recitation
• Charity and social responsibility
• Ethical self-regulation

This reflects Muslims’ commitment and self-control, helping them to prepare for a fresh start and focus on their deen (faith).

What also adds a distinct character to this commemoration is that it is not fixed on the Gregorian calendar, instead, it follows the Islamic calendar, which is based on a 12-month lunar year of approximately 354 days. And in this calendar, Ramadan is the 9th month, which also begins earlier each year, as it is also 11 days shorter than the solar year.

This difference from the solar year causes Ramadan to move through the seasons, returning roughly to the same period only after about 33 solar years.

As a tradition, the month begins and ends with the sighting of the new crescent moon — which reflects the lunar foundation of the Islamic calendar, where each month is determined not simply by counting days, but by the moon’s visible cycle in the sky.

In this way, the start of Ramadan depends not only on counting days but on confirming the moon’s first appearance.

A light of faith

Now, the basis — which is the moon sighting, does not refer to the moon simply being present overhead but by specifically pointing to the first visible crescent, known in Arabic as Ru’yat Al Hilal, which marks the beginning of a new month in the Hijiri calendar.

While other countries follow their own moon sightings by using astronomical calculation for lunar phases, and others also rely on traditional local sightings for the confirmation.

The crescent must set after the sun for the moon to be visible as this allows the sky to be dark enough to spot the small silver of the moon. And from this, if the crescent moon is seen, the new month begins the following day; if not, the month is completed as 30 days.

Tracing the crescent

This confirmation, however, is not always simple, because the crescent’s visibility depends on specific astronomical conditions.

The astronomical new moon happens when the moon is directly between the Earth and the sun. At this stage, the moon cannot be seen from the ground since its illuminated side is facing away from us.

However, for the commemoration of Ramadan, what matters is the first time the thin crescent becomes visible after sunset.

According to astronomers, there are factors that impact the visibility of the crescent:

• Elongation, or how far is the moon from the sun. 
• Altitude, or how high the moon is above the horizon at sunset. A higher moon is easier to spot because it is less affected by haze near the horizon, while a low crescent can be hidden in the bright glow of the evening sky.
• Lag time, which refers to the time between sunset and when the moon sets.

Together, these factors explain why the crescent is seen in some places but are not seen in others.

Moon swings

This is also why the beginning of the Ramadan can differ across countries, even within the same year.

Because moon visibility depends on geography and timing, Ramadan does not always begin on the same day worldwide. In many countries, official moon sighting takes place on the 29th of Shaaban to verify testimony from accredited observers before issuing a formal announcement of the start of Ramadan.

While regional differences persist, moonsighting continues to represent a blend of religious tradition, scientific assessments, and official verification.

A month of reflection

And through this blend, the crescent moon continues to serve as the signal for one of Islam’s most sacred months. Still, Ramadan’s beginning is defined by this simple yet profound moment.

Until today, it continues to begin not with a fixed calendar date but with the confirmation of the moon’s appearance — reminding Muslims that sacred time remains tied to both faith and the natural rhythms of the universe.