How Moon Sighting Works: The Crescent, the 29th Evening and Visibility

Every Islamic month begins with a sighting — or with the decision that there was nothing to see. For something that shapes the start of Ramadan and the date of Eid, the process is surprisingly unfamiliar to most people. This guide explains, step by step, what happens on the evening of the 29th, what the observers are looking for, and why it is genuinely difficult.

The new moon and the crescent are not the same thing

The phrase “new moon” causes a lot of confusion, because astronomers and Islamic usage mean different things.

• The astronomical new moon, or conjunction, is the moment when the moon passes between the Earth and the sun. At that moment its sunlit side faces away from us and it is completely invisible.
• The crescent, the hilal (هِلال), is the first thin sliver of the sunlit moon that becomes visible after conjunction, seen just after sunset.

The Islamic month begins with the hilal, not the conjunction. In the hadith, the Prophet ﷺ said: “Fast when you see it, and end the fast when you see it. If it is obscured, complete the count” (Sahih al-Bukhari 1909; Sahih Muslim 1081). The “it” is the crescent.

That gap — from invisible conjunction to visible crescent — is the heart of every disagreement about start dates.

What happens on the 29th evening

On the 29th day of each Islamic month, sighting committees and volunteers prepare to look for the crescent.

1. They find the right place. A clear, low western horizon, ideally elevated and away from city lights and haze. Coastal hills and deserts are popular.
2. They wait for sunset. The crescent is never visible before sunset; the sky is far too bright.
3. They search in a narrow window. The young crescent sits just above where the sun set, and it sets soon after the sun. The window to see it is often only 10 to 40 minutes.
4. They report. Anyone who believes they have seen the crescent reports it to the local committee or court, giving details such as time, position and the shape of the crescent.
5. The authority decides. Testimonies are examined. If a sighting is accepted, the new month begins that evening. If not, the month is completed to 30 days.

In Saudi Arabia, sightings are reported to the Supreme Court. In Pakistan, the Ruet-e-Hilal Committee meets with zonal committees across the country. In the UK and North America, a mix of organisations either look locally, follow another country, or rely on calculation.

Why the crescent is so hard to see

A crescent that is a day old is extremely thin and faint, and it sits in the brightest part of the twilight sky. Whether it can be seen depends on several factors.

Moon age

The age of the moon is the time since conjunction. A crescent younger than about 15 hours has essentially never been verified with the naked eye; most naked-eye sightings involve moons older than 18–24 hours. Age on its own is a rough guide, though — two crescents of the same age can be very different in visibility.

Elongation

Elongation is the angular distance between the moon and the sun. The further the moon is from the sun, the thicker the lit crescent and the darker the sky around it. Astronomers have long noted that below about 7 degrees of separation, the crescent is too thin to form a visible arc — a threshold often called the Danjon limit.

Lag time

Lag is the time between sunset and moonset. If the moon sets only a few minutes after the sun, there is no chance of seeing it in a dark-enough sky. A lag of at least 30–40 minutes greatly improves the chances.

Altitude and the horizon

The moon’s height above the horizon at sunset matters, as does the observer’s horizon. Dust, humidity, pollution and cloud near the horizon can make a theoretically visible crescent impossible to see.

Location

Because the moon moves relative to the sun, the crescent becomes easier to see as the day progresses around the world. In general, a crescent that is invisible in the Middle East may be visible a few hours later in West Africa or the Americas. This is why sighting reports often come first from the western parts of the world.

Visibility predictions

Astronomers can calculate where a crescent should be visible on a given evening. Several criteria are used, developed by researchers including Yallop, Odeh and others, based on thousands of recorded observations. Visibility maps typically divide the world into zones:

• easily visible to the naked eye;
• visible with optical aid, may be seen with the naked eye;
• visible only with optical aid;
• not visible.

These predictions are very good but not perfect at the margins. They are used in three ways: to help committees decide where and when to look, to evaluate testimonies (a claim to have seen a crescent where it was below the horizon is unlikely to be accepted), and by some organisations as the basis of calculated calendars.

Naked eye, binoculars or telescope?

Muslim authorities differ on whether sightings made with binoculars or telescopes count:

• Some accept only naked-eye sightings, following the literal sense of “seeing”.
• Many accept sightings with optical aid, since the instrument only helps the eye see what is there.
• A growing number use cameras and CCD imaging, which can detect very young crescents.

The choice matters: a crescent visible only through a telescope on the 29th evening can mean a month starts a day earlier than in places that require the naked eye.

When the decision is made — and why it is late

Because the sighting can only happen after sunset on the 29th, the decision about whether tomorrow is 1 Ramadan or 30 Sha’ban is usually announced a few hours after sunset that evening. For people who need to plan — schools, employers, families travelling for Eid — this is inconvenient but unavoidable in a sighting-based calendar.

That is why calculated dates such as Umm al-Qura are so widely used for planning: they tell you the expected date months in advance. The final date still depends on your community’s method. For 1448 AH, the expected dates are:

• 1 Ramadan: Monday 8 February 2027 — the crescent would be sought on the evening of Sunday 7 February.
• 1 Shawwal (Eid al-Fitr): Tuesday 9 March 2027 — crescent sought on the evening of Monday 8 March.
• 1 Dhul-Hijjah: Friday 7 May 2027 — with Eid al-Adha expected on Sunday 16 May.

Misconceptions about sighting

“If it was a full moon on the 15th, the crescent must be visible on the 29th.” The moon’s cycle is not exactly 29 or 30 days, and visibility depends on geometry and weather, so this rule of thumb fails often.

“A large crescent on the second night proves the month started late.” A crescent that looks big on its first visible evening may simply have been just too thin to see the evening before. Size alone does not prove a missed sighting.

“Sighting is unscientific.” Crescent observation is an empirical science in its own right. Modern visibility criteria were built from the records of observers, many of them organised by Muslim astronomy groups.

What you can do as an individual

You do not need to be on a committee to take part in the tradition. If you would like to look for the crescent yourself:

1. Check the Islamic date and confirm that tonight is the 29th evening.
2. Find your local sunset time — the Maghrib time on our prayer times page is a good guide.
3. Go somewhere with a clear western horizon, before sunset.
4. Look slightly to the left or right of where the sun set (depending on season), low in the sky, in the 20–40 minutes after sunset.
5. Binoculars help — but never point them at the sun before it has fully set.

Even when the crescent is not seen, the experience explains the calendar better than any article can. The month may begin tomorrow or the day after; either way, it will begin with the moon.