How the New Crescent Moon (Hilal) Is Sighted

The start of Ramadan, Eid al-Fitr and Eid al-Adha depends on the hilal, the first thin crescent of the new moon. The Prophet ﷺ said: "Start fasting on seeing the crescent, and stop fasting on seeing the crescent; and if it is hidden from you, complete thirty days of Sha'ban" (Sahih al-Bukhari 1909). Here is what actually happens in the sky on that 29th evening.

New moon is not the crescent

Astronomers call the moment when the moon passes between the Earth and the sun the conjunction, or astronomical new moon. At that moment the moon's lit side faces away from us and it cannot be seen at all. Over the following hours it moves east of the sun and a sliver of its sunlit side becomes visible as a crescent, but only once it is far enough from the sun and the sky is dark enough.

What makes the crescent visible?

• Age of the moon: the time since conjunction. A crescent younger than about 15–20 hours is very rarely seen with the naked eye.
• Elongation: the angle between the sun and the moon. Below about 7° the crescent is too thin to form a visible arc.
• Lag time: how long the moon stays above the horizon after sunset. The longer the lag, the darker the sky when the moon is still up.
• Altitude and conditions: a higher moon, a clear horizon and clean air all help; haze and clouds can hide a crescent that is astronomically visible.

Astronomers have turned these factors into visibility criteria. The HM Nautical Almanac Office and the International Astronomical Center publish maps that show, for each month, where the crescent should be visible to the naked eye, with optical aid, or not at all.

Why the crescent is seen first in the west

As the Earth turns, places further west see sunset later, by which time the moon is older and further from the sun. A crescent that is impossible to see in Asia on a given evening may be easy to see in Africa or the Americas a few hours later. This is one reason countries can begin a month on different days.

How decisions are made

Countries handle this in different ways. Some, like Morocco and Pakistan, rely on sighting committees and local reports. Saudi Arabia's Supreme Court announces Ramadan, Shawwal and Dhu al-Hijjah after considering sighting testimony. Others, such as Turkey, use calculated criteria decided in advance, while many Muslim communities in the West follow either a calculation or the announcement of another country. You can read more in why Islamic dates differ between countries.

Dates on HijriTime

HijriTime uses the calculated Umm al-Qura calendar, so the dates are known in advance. On the evening of the 29th, always check the announcement followed by your mosque or national authority for Ramadan and the Eids. You can follow the upcoming dates on our countdowns.