MOON SIGHTING & THE HIJRI CALENDAR
How an Islamic month begins
A clear Sunni guide to crescent observation, astronomical calculation, local decisions, and why sincere Muslim communities may begin a month on different days.
The essential point: Future Hijri dates are predictions. Worship tied to the start of a month follows the determination adopted by the appropriate local community or recognized authority.
THE SUNNI FOUNDATION
Observe the crescent—or complete thirty days
The Islamic calendar is lunar. The Qur’an describes the moon’s phases as measures of time, and the Prophet ﷺ instructed Muslims to begin and end the Ramadan fast upon sighting the crescent. If visibility is obscured, the current month is completed as thirty days.
This Prophetic framework establishes actual crescent sighting as the basis for ritual month beginnings. Astronomical knowledge can help predict visibility, rule out impossible reports, and organize observation, while Sunni jurists differ over the extent to which calculation may independently establish a month.
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A lunar month has 29 or 30 days
It never has 28 or 31. The new month begins at sunset when its commencement has been established—not at midnight.
FROM CONJUNCTION TO VISIBILITY
What observers are looking for
The birth of the astronomical new moon and the first visible crescent are not the same event. Visibility depends on several interacting conditions.
01
Conjunction
The moon passes between Earth and the sun. The crescent is generally not visible at that instant.
02
Sunset geometry
Moon age, altitude, elongation, and the interval between sunset and moonset affect possible visibility.
03
Local conditions
Cloud, haze, dust, elevation, horizon clarity, eyesight, and optical aid can affect an observation.
04
Testimony
A recognized authority assesses sighting reports according to its evidentiary and legal standards.
THE LUNAR CYCLE
From new moon to waning crescent
The moon does not produce its own light. As it orbits Earth, we see changing portions of its sunlit half. These appearances are phases—not changes in the moon’s physical shape.
01
Conjunction is not a sighting
The astronomical new moon occurs when the moon is aligned near the sun. Its illuminated side faces away from Earth, so it is not the crescent observers seek.
02
The hilal comes afterward
The first waxing crescent may become visible after sunset once geometry and atmospheric conditions allow. Its visibility can vary by place.
03
Phases continue all month
The moon waxes toward fullness, then wanes. A complete phase cycle averages about 29.5 days, producing Hijri months of 29 or 30 days.
WHY DATES DIFFER
Several recognized approaches
Local sighting
A community begins the month based on a valid sighting within its locality or region. This gives weight to differing horizons and local religious authority.
Broader or global sighting
A verified sighting elsewhere is accepted for a wider area, sometimes internationally, subject to the adopted juristic view and authority.
Visibility criteria
Astronomical models estimate where a crescent could be seen. They can guide observers and help evaluate reports without necessarily replacing testimony.
Calculated calendar
Some organizations use predetermined criteria to establish dates. This offers consistency and planning, though Sunni scholars differ on its use for ritual beginnings.
LEGITIMATE DIFFERENCE
Unity does not require pretending every method is identical
Differences can result from geography, weather, whether distant sightings are accepted, evidentiary standards, and juristic methodology. A one-day difference does not automatically prove carelessness or bad faith.
Practical guidance for worshippers
- Follow a trusted local mosque, council, or recognized authority.
- Avoid creating conflict in families and communities over a legitimate scholarly difference.
- For fasting and Eid, communal unity carries practical and religious importance.
- Travelers should ask how their destination handles a change in observed dates.
- When personal circumstances are complex, consult a qualified local scholar.
ISLAMCAL DATE LABELS
Know what kind of date you are viewing
Every important date on IslamCal will identify its status so a forecast is never mistaken for a religious announcement.
Confirmed
An authority has formally established the date for the place or audience stated.
Calculated
The date follows a named mathematical calendar or predetermined criterion.
Estimated
A planning date that remains subject to the month’s actual determination.
Locally observed
A date established from a sighting or decision for a stated local community.
COMMON QUESTIONS
Clear answers without oversimplifying
Why can two nearby mosques differ?
They may follow different authorities or juristic policies concerning local and distant sightings, calculations, or testimony.
Can a crescent be seen before conjunction?
A claimed new-month crescent before conjunction is astronomically impossible; experts and authorities may use this fact when assessing testimony.
Does IslamCal declare Ramadan or Eid?
No. IslamCal explains methods and reports date status. Religious announcements belong to the relevant recognized authorities.
A responsible observation checklist
- Confirm the correct date, location, sunset, and moonset times.
- Choose a safe site with an unobstructed western horizon.
- Never look directly at the sun through binoculars or a telescope.
- Record the time, direction, duration, weather, and optical aid used.
- Do not confuse aircraft trails, clouds, glare, or bright planets with the crescent.
- Submit reports to the appropriate body rather than treating a social post as confirmation.
Explore the Hijri year with confidence
Use this methodology alongside the month-by-month guide, where important dates and observances are clearly explained.