The astronomical Hijri method is a mathematical conversion method. It uses the lunar month cycle, Julian-day calculations, and numerical rules for month and year lengths to calculate Hijri dates without waiting for a monthly crescent observation.

Miqat presents this method as an independent tabular/arithmetical calculation rather than the Umm al-Qura method. The two methods may differ by a day or two. The word “astronomical” here does not mean that Miqat is conducting live crescent observations or issuing a religious announcement.

Calculated Hijri calendars developed alongside astronomy, astronomical tables, and the practical need to know dates in advance. Printed tables and computers later made numerical conversion fast and reproducible for civil dating, historical work, and digital applications.

Several models exist. Some are fixed tabular systems, while others attempt to estimate crescent visibility from conjunction, altitude, elongation, and moonset lag. Consequently, astronomical methods do not form one universally identical standard.

The engine maps the Hijri date to a unified day count and connects that count to the Gregorian calendar through mathematical Hijri-calendar formulas. Each lunar month is treated as 29 or 30 days, and the year contains 12 months.

The model uses a 30-year numerical cycle with 11 leap years. In a leap year, the extra day is assigned to Dhu al-Hijjah. This makes conversion fast and reproducible, but it does not model local visibility or weather conditions.

1. Convert the input date to a unified day value.

2. Apply the Hijri year rule and 30-year cycle to locate the date within the lunar year.

3. Determine the month and day from the calculated month lengths.

4. Convert the result to Gregorian or another Miqat calendar.

5. Show a notice explaining that the calculated result may differ from Umm al-Qura or an official announcement.

Leap-year example: when a Hijri year falls among the leap years of the 30-year cycle, one day is added to Dhu al-Hijjah, making it 30 days instead of 29 in the tabular model.

Method-difference example: the astronomical calculation may return one date for the beginning of a month while Umm al-Qura returns a neighboring date because the two methods use different start-of-month rules.

Conjunction versus sighting: conjunction is an astronomical instant and does not necessarily mean that a visible crescent already exists. After conjunction, the Moon may need time to move away from the Sun’s glare; visibility also depends on location, altitude, and atmospheric conditions.

Miqat’s astronomical method is a general mathematical date-conversion model, while Umm al-Qura is a specific Saudi civil system using its adopted Umm al-Qura rule and Makkah reference described by its official website. The results often agree but can differ on some dates.

The astronomical method alone does not determine the beginning of Ramadan, Shawwal, or Dhu al-Hijjah. For these observances, users should follow the competent authority’s official announcement because calculation, sighting, and legal determination are related but not identical.

The method is useful for quick conversion, historical research, calendar tables, and applications that need a consistent and reproducible lunar date. It also helps users compare calendar systems and understand a date’s position within the lunar year.

For official religious observances, the calculated result should not replace the competent authority’s announcement. Miqat labels the method clearly so users can identify the source of a result and compare it with Umm al-Qura.