Moon Sighting Explained: Why Ramadan Starts on Different Days

Every year the same question appears: why did one country start Ramadan on Monday and the next on Tuesday? The answer is partly astronomy and partly a difference of method. This guide explains both in plain terms, so the one-day gaps on the Islamic calendar make sense.

The hadith that sets the rule

The Prophet (peace be upon him) said: fast when you see it, and break the fast when you see it; and if it is hidden from you, complete thirty days (Bukhari 1909 / Muslim 1081). "It" is the hilal, the thin new crescent seen just after sunset. The Qur'an calls the crescents timings for people and for the pilgrimage (2:189).

From this hadith come three practical rules that every method tries to honour:

1. A month is 29 or 30 days, never more or less.
2. On the evening of the 29th, look for the crescent. If it is seen, the new month begins at that sunset.
3. If it is not seen (cloud, haze, or simply too young), complete thirty days and the new month begins the following sunset regardless.

The astronomy, in simple terms

The moon orbits the Earth about once every 29.5 days. The moment it passes between the Earth and the sun is the new moon or conjunction. At that moment it cannot be seen: its lit side faces away from us and it sits next to the sun in the sky.

After conjunction the moon moves east of the sun, and each day it sets a little later and shows a slightly wider sliver. The first evening on which the sliver can be seen is the hilal. Three numbers decide whether it can be seen:

A fourth is lag time: how many minutes the moon sets after the sun. A lag of 20–40 minutes gives a dark enough sky; a lag of 10 minutes does not.

These numbers differ by location on the same evening. A crescent that is 22 hours old and 8 degrees high in Morocco may be only 16 hours old and 4 degrees high in Indonesia, because sunset in Indonesia came several hours earlier. That is why the crescent is first seen in the west of the Muslim world and often not in the east on the same date.

Calculation, local sighting, global sighting

Astronomical calculation

Some authorities define the month by a rule computed in advance. Saudi Arabia's Umm al-Qura calendar begins the month when conjunction occurs before sunset at Makkah and the moon sets after the sun on that evening. Turkey's Diyanet and several European bodies use criteria based on predicted visibility (for example a minimum altitude and elongation somewhere on Earth). The Fiqh Council of North America adopted a calculated calendar in 2006.

Advantages: dates known years ahead, no disputes over cloud or eyesight. Objection raised by other scholars: the hadith speaks of seeing, and a calculated criterion like Umm al-Qura's can place the month start a day before any human could see the crescent.

Local or regional sighting

Many countries (Morocco, Pakistan, India, Bangladesh, Indonesia, Malaysia, Nigeria, South Africa and others) have official committees that take testimony from observers on the evening of the 29th. If the crescent is confirmed, the month begins; otherwise it is completed at thirty days. Some combine sighting with calculation, rejecting reports that are astronomically impossible.

Global sighting

Some communities, including many masjids in the UK and North America, accept a confirmed sighting from anywhere in the world, often in practice following the Saudi announcement. The reasoning is that the hadith addresses the Muslims as one community.

Ja'fari practice

Ja'fari jurists generally require sighting as well, with differences on whether a sighting in another region that shares part of the night is accepted; follow your own marja' or community.

Why countries differ: a worked example

Take Ramadan 1448. The astronomical new moon is on 6 February 2027 (the day of an annular solar eclipse, which is simply the new moon passing in front of the sun).

• At sunset in Makkah on 6 February, the moon is only a few hours old and sets with or before the sun, so Umm al-Qura's criterion is not met that evening. The calendar therefore gives 1 Ramadan as Monday 8 February 2027: the month begins at sunset on Sunday 7 February.
• On the evening of 7 February, the moon is over 24 hours old across the Middle East and Africa and comfortably visible in clear skies, so sighting-based countries from Morocco to Pakistan are expected to see it and also begin Ramadan on Monday 8 February.
• Further east, in Indonesia and Malaysia, sunset on 7 February comes earlier, so the moon is younger and lower; but in most years a 20-plus-hour moon is still seen or accepted by calculation, so 8 February remains likely there too.

Ramadan 1448 is therefore expected to be a year of broad agreement. The difference tends to appear at the end of the month: Umm al-Qura gives Ramadan 29 days with Eid on Tuesday 9 March, while any country that does not sight the Shawwal crescent on the evening of 8 March will complete thirty days and celebrate Eid on Wednesday 10 March. Block both days if you can; see Eid al-Fitr 2027.

What to do as an ordinary Muslim

• Follow the announcement of your country's authority or the masjid you pray with. Scholars across the schools agree that a community should fast and celebrate together.
• Treat the dates on this site, and on your phone, as expected: they follow Umm al-Qura. The Hijri converter and the Ramadan timetable are built on that calendar; your local announcement may shift them a day.
• If you move between communities (for example you travel from a sighting country to a calculation country during Ramadan), scholars generally advise following the community you are in; ask a scholar you trust about completing or shortening the fast count.
• Do not argue about it on the night. A difference of a day is as old as the hadith about completing thirty.

Reading a sighting announcement

Announcements typically say one of three things:

1. "The crescent was sighted; tomorrow is the first of the month." The month begins at that sunset.
2. "The crescent was not sighted; the month will complete thirty days." The new month begins the following sunset.
3. "Based on astronomical calculation, the first of the month will be on…" A calculated decision made in advance.

Whichever your community uses, the Qur'an's description still stands: the phases of the moon are there so people may know the number of years and the reckoning (10:5). The reckoning is shared; only the observers' horizons differ. The Hijri calendar explained page covers what happens after the month begins.