The new crescent
An Islamic month begins with the hilal, the thin new crescent Moon seen in the western sky just after sunset. After the astronomical new moon (conjunction), when the Moon is between the Earth and the Sun and invisible, it takes time for the Moon to move far enough from the Sun for a sliver of its lit side to be visible in the twilight. Usually the crescent becomes visible somewhere on Earth within about a day or two of conjunction.
The 29th evening of each month is the key moment. If the crescent is seen that evening, the next month begins at that sunset. If it isn’t, the current month completes 30 days.
Why sighting varies
Whether the crescent can be seen depends on:
- the Moon’s age and its angular distance from the Sun,
- how long the Moon stays up after sunset,
- the observer’s location: the crescent is generally easier to see further west, because the Moon is older by the time the Sun sets there,
- weather and haze: clouds or dust can hide a crescent that would otherwise be visible.
So on the same evening the crescent may be seen in one country and not in another, or in one part of India and not another. That’s why the start of Ramadan or Eid sometimes differs by a day between countries, or even between communities in the same city.
The approaches communities follow
Muslim communities and scholars have developed several approaches, each with its own reasoning:
Local sighting. The month begins when the crescent is sighted in one’s own country or region. Many communities in India follow announcements by local or regional moon-sighting (Ruet-e-Hilal) committees and scholars, who receive and verify sighting reports on the 29th evening.
Wider or global sighting. Some scholars accept a reliable sighting from anywhere, or from a wider region, as establishing the month for everyone who learns of it.
Following Makkah. Some communities follow the dates announced in Saudi Arabia, particularly for the days of Hajj and Eid al-Adha.
Astronomical calculation. Some institutions accept calculation of the crescent’s visibility, or of the Moon’s position at sunset, in place of physical sighting, which lets calendars be fixed in advance.
Tabular calendars. Some traditions, such as the Dawoodi Bohra community, use a fixed arithmetic cycle of month lengths. See Shia and Bohra calendars.
Each approach rests on serious scholarly reasoning. OIOA doesn’t take sides; it offers calendar options so you can follow the one your community uses.
The Umm al-Qura calendar
The Umm al-Qura calendar is the official calculated calendar of Saudi Arabia, named after Umm al-Qura University in Makkah. Under its current rule, a month begins on the evening of the 29th if, as seen from Makkah, the conjunction has already taken place before sunset and the Moon sets after the Sun. Because these are computable, the Umm al-Qura calendar is known years in advance.
It’s widely used for civil purposes in Saudi Arabia. For religious occasions such as Ramadan, Eid and the days of Hajj, Saudi Arabia’s authorities consider moon-sighting reports, and announced dates can differ by a day from the pre-calculated calendar.
What this means for you
- For everyday dates, any calculated calendar gives you a good guide to the Hijri date.
- For Ramadan, Eid al-Fitr and Eid al-Adha, follow your local announcement. Use the calculated date to know when to expect the announcement.
- If relatives abroad celebrate on a different day, that’s expected, not an error.
- The evening of the 29th is when to listen for news.
In OIOA
On the Islamic Home screen, OIOA offers the Islamic calendar with Makkah (Umm al-Qura), Shia and Bohra (Dawoodi, Misri) options, calculated on your phone. Where your community begins a month by sighting, please follow your local announcement, and treat OIOA’s date as a guide. See also Ramadan and Eid al-Fitr.
Common questions
What is Chand Raat?
Chand Raat, “the night of the moon”, is the evening when people look for the new crescent, especially the one that ends Ramadan and announces Eid al-Fitr. In India it’s a festive evening of shopping, mehndi and preparations, while everyone waits for the announcement.
Why does Eid sometimes fall a day apart in India and the Gulf?
The crescent is generally easier to see further west, and different authorities follow different approaches: local sighting in India, and Saudi Arabia’s own determination for the Gulf. So Eid in India often falls a day after Eid in the Gulf countries.
Can the crescent be predicted?
Astronomers can predict with good accuracy whether a crescent should be visible from a given place on a given evening, using the Moon’s age, its distance from the Sun and its altitude at sunset. Whether such predictions may replace physical sighting is a question on which scholars differ.
Is the Umm al-Qura calendar used in India?
Some people and organisations in India refer to it, especially for an overview of the year, but most religious occasions in India follow local sighting. OIOA offers Umm al-Qura as one of its calendar options.
What should I do if my family follows a different approach from my mosque?
That’s a matter for your family and scholars. OIOA simply lets each person choose the calendar option they follow.
Key terms
- Hilal: the new crescent Moon.
- Conjunction: the astronomical new moon, when the Moon is between Earth and Sun.
- Ruet-e-Hilal: moon sighting; also the name of committees that receive and verify reports.
- Umm al-Qura: Saudi Arabia’s calculated calendar.
A note on unity
Differences over the start of a month are sometimes a source of tension. They are also a sign of how seriously communities take their practice. Whatever day your community observes, the occasion is shared.
If your community follows a particular committee or scholar, their announcement is the one that counts for you.