Rabi II
Enable an AI agent to recognise Rabi II and resolve, compare and use its yearly occurrences without confusing calendar conventions or local declarations.
Research draft, second pass
A second pass drafted this model: the structure a model of this thing needs, and what is known about it in the world. The line under this one says how the second half was obtained - researched against sources, or recalled without web access, in which case nothing here was read anywhere and every claim is a lead to verify. Unreviewed either way.
Researched by: Codex + Grok
Purpose and description
Enable an AI agent to recognise Rabi II and resolve, compare and use its yearly occurrences without confusing calendar conventions or local declarations.
Rabi II (Rabi' al-Thani / Rabi' al-Akhir) is the fourth month of the Islamic lunar hijri calendar, a 29- or 30-day civil and religious period whose start is fixed by lunar crescent sighting or by a tabulated civil calendar, not by the Gregorian year.
It can be Normalise an attested Rabi II name while preserving its source form.; Identify a yearly occurrence using a Hijri year and calendar context.; Validate a day number against that occurrence's resolved length.; Convert qualified Rabi II dates into Gregorian dates or intervals with stated assumptions.; Compare competing boundary assignments and explain their differing methods or authorities.; Schedule or revise dependent actions according to the required level of date certainty..
Distinguishing features
It denotes month four of the Islamic lunar calendar; the II distinguishes it from Rabi I, rather than indicating month two.
Rabi al-Thani and Rabi al-Akhir are alternative names for this month, subject to spelling and language verification. [Islamic Relief](https://www.islamic-relief.org.uk/resources/islamic-calendar/rabi-al-thani/)
A reference to Rabi II alone identifies a recurring month; a particular interval additionally requires a Hijri year and calendar context.
Its spring-related name does not restrict it to a solar season: Islamic lunar months move through the solar year. [Islamic calendar explanation](https://www.timeanddate.com/calendar/islamic-calendar.html)
A Gregorian date range is a mapping of a qualified occurrence, not a permanent property of Rabi II.
Scope
+ Recognition of Rabi II and evidenced alternative names
+ Position between Rabi I and Jumada I in the Hijri month sequence
+ Year-specific occurrences qualified by calendar method and applicable authority
+ Month boundaries, day validity and Gregorian correspondence
+ Uncertainty, disagreement and revisions affecting use of Rabi II dates
- The complete Islamic calendar and its general calculation algorithms
- Astronomical observation equipment and crescent-visibility physics
- Religious observances, their doctrines and rules of participation
- Historical events merely dated within Rabi II
- The governance of organisations that issue calendar declarations
Characteristics
- Hijri month position
- Fourth month of the Islamic lunar calendar Prevents interpretation of II as the month number two.
- Attested name form
- Rabi II; Rabi al-Thani; Rabi al-Akhir; other source-attested language and spelling variants Supports recognition across records while preserving the original wording.
- Occurrence year
- A specified Hijri year with an explicit era Separates the recurring month concept from a particular occurrence.
- Calendar determination method
- Observation-based; calculated astronomical; tabular; other documented method; unknown Explains how boundaries were obtained and whether two mappings are comparable.
- Applicable authority and community
- Named calendar issuer or decision authority and the community or jurisdiction adopting its dates Determines which occurrence boundaries apply to the intended use.
- Occurrence length
- 29 or 30 calendar days when resolved; otherwise unresolved Controls whether a proposed day 30 exists in the selected occurrence.
- Boundary resolution
- Unresolved; forecast; calculated under a specified convention; declared; disputed; superseded Prevents a forecast or convention-specific result from being presented as a universally settled date.
- Boundary interval
- Start inclusive and next-month start exclusive, with location, time zone and day-boundary convention where needed Enables precise membership checks and scheduling.
Where this came from
wikidata · CC0 1.0
Drafted structure
Bundle to layer to finding to question, as the second pass will find it: 6 bundles · 11 layers · 18 findings · 29 questions.
Rabi II recognition Establish which month a name or date expression denotes.
The paired Rabi names and Roman numeral can produce incorrect month identification.
Rabi name equivalence
Recognise alternative names without silently merging ambiguous expressions.
Attested Rabi II label
Record the original label, its language and the evidence supporting its interpretation as Rabi II.
- Does the expression explicitly identify Rabi II, Rabi al-Thani or Rabi al-Akhir, or does it merely say Rabi? definition
- Which source establishes that this spelling or local name denotes Rabi II? provenance
Fourth-month position
Disambiguate the second Rabi month from the second month of the year.
Rabi sequence check
Use month position and neighbouring names to detect misidentification.
- Does the record place this month fourth, after Rabi I and before Jumada I? definition
- Does an accompanying numeric date conflict with the written Rabi II label? boundary
Yearly Rabi II occurrence Distinguish the recurring month from a calendar-specific occurrence.
Rabi II alone cannot identify a Gregorian interval or determine whether the month is current.
Hijri year binding
Attach an occurrence to its explicit year and era.
Occurrence identification
Record whether the reference means Rabi II generally or Rabi II in a particular Hijri year.
- Is this a recurring reference to every Rabi II or one occurrence in a specified Hijri year? definition
- Is the year and its era explicit, inferred from context or still missing? provenance
Calendar context binding
Identify the method and adopted calendar that qualify the occurrence.
Applicable Rabi II calendar
Keep observation-based declarations, calculated calendars and tabular results distinguishable.
- Which calendar method and issuer determine this occurrence of Rabi II? provenance
- For which community, jurisdiction or historical context are those dates applicable? boundary
Rabi II boundaries Resolve entry from Rabi I and exit into Jumada I.
The validity of dates and the duration of the occurrence depend on both transitions.
Rabi I to Rabi II
Establish the start of the selected occurrence.
First-day determination
Record the evidence and status of the assigned first day of Rabi II.
- What declaration, observation report or calculation assigns the first day of this Rabi II? provenance
- Is that assignment a forecast, a result under a fixed convention or an adopted declaration? definition
Rabi II to Jumada I
Establish the end of the occurrence and valid final day.
Last-day validity
Resolve whether this occurrence contains day 30 from the applicable calendar evidence.
- Does this occurrence contain 29 or 30 days under the selected calendar? measurement
- What evidence establishes the transition into Jumada I and therefore whether 30 Rabi II is valid? provenance
Rabi II date mapping Translate qualified Rabi II dates into usable civil dates and intervals.
Date conversion must account for year, calendar method and the meaning of a day's boundary.
Gregorian correspondence
Preserve the assumptions behind a Gregorian mapping.
Qualified conversion
Record the conversion basis and any unresolved alternative dates.
- Which Gregorian date or candidate dates correspond to the specified Rabi II day under the selected calendar? measurement
- Which published calendar or converter version supports that mapping? provenance
Evening and civil day
Distinguish a displayed civil date from the full interval intended by a Hijri day.
Day interval interpretation
Record whether the use requires a sunset-based interval, a civil date label or another explicit convention.
- Does this use of a Rabi II date denote a sunset-to-sunset interval or a civil calendar date label? boundary
- Which location, time zone and boundary rule are required to determine whether an instant falls within that day? measurement
Rabi II operational use Determine when a Rabi II date is sufficiently resolved for an intended action.
Calendar disagreement and later declarations can change scheduling without changing the identity of the month.
Competing month assignments
Retain differences between applicable calendar determinations.
Assignment selection
Choose an occurrence mapping according to the intended user's calendar context while preserving alternatives.
- Do the competing Rabi II boundaries reflect different methods, adopted authorities or revisions by the same issuer? provenance
- Which assignment should govern this action, and what explicit user or organisational rule selects it? action
Rabi II dependent actions
Connect date certainty to scheduling and references to separately modelled observances.
Action readiness and revision
Record whether an action can use a forecast and what must happen if the adopted dates change.
- Can the intended action use a provisional Rabi II date, or must it await an adopted declaration? action
- Which dependent schedules must be recalculated if the start or length of Rabi II changes? action
- If an action concerns an observance within Rabi II, which separate observance model establishes its date and applicable community? boundary
Evidence and external alignment What the world already says about this thing, gathered so the model can be checked against it.
A model that cannot be lined up against existing standards, identifiers and practice cannot be adopted by anyone who already uses them.
Reported evidence
Findings from the breadth pass, kept separate from the structural claims.
Kinds and varieties
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Rabi' al-Thani as a lunar-sighted religious month
- Rabi' al-Thani as a tabulated civil hijri month (Umm al-Qura and similar)
- Rabi' al-Akhir as the same month under its alternate Arabic name
- Rabi II as a Latin-numeral calendar label (Rabi II / Rabi' II)
- Which of these kinds and varieties hold for the sense of Rabi II this model covers, and on what evidence? provenance
Identifiers and schemes
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Wikidata - Q186543 (Rabi' al-Thani) - Wikidata item for the fourth Islamic month.
- ISO 8601-2 / hijri month numeral - month 04 in a Hijri year (AH-YYYY-04) - Civil hijri dates encode this month as 04; day count is 29 or 30.
- Arabic name pair - ربيع الثاني / ربيع الآخر - Rabi' al-Thani and Rabi' al-Akhir are both standard Arabic names for the same month.
- Which of these identifiers and schemes hold for the sense of Rabi II this model covers, and on what evidence? provenance
Standards and regulation
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Saudi Umm al-Qura calendar (Umm al-Qura, King Abdulaziz City for Science and Technology) - tabulated civil hijri dates used for Saudi official business.
- Crescent-sighting practice under national moon-sighting committees (varies by country; not a single ISO standard) - determines the religious start of the month.
- ISO 8601-2:2019 (ISO) - calendar extensions that can represent Islamic calendar dates in information systems.
- Which of these standards and regulation hold for the sense of Rabi II this model covers, and on what evidence? provenance
Real-world use
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Printed and digital hijri calendars label the fourth month Rabi' II / Rabi' al-Thani for civil dating of contracts, government gazettes, and mosque notices.
- Muslim communities use it as a dating frame for births, deaths, waqf deeds, and historical chronicles written in AH.
- Some regions mark popular commemorations in this month (for example Mawlid-related or saint-day observances that fall after Rabi' I), but these are local custom, not a canonical ritual of the month itself.
- Software and almanacs convert AH-YYYY-04-DD to Gregorian dates; the mapping shifts ~11 days earlier each solar year.
- Which of these real-world use hold for the sense of Rabi II this model covers, and on what evidence? provenance
Typical measurements
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Month length - 29 or 30 - day
- Position in hijri year - 4 of 12 - ordinal month
- Mean synodic offset vs Gregorian - about 10-12 days earlier each solar year - day per year
- Day-of-month numbering - 1-29 or 1-30 - hijri day
- Which of these typical measurements hold for the sense of Rabi II this model covers, and on what evidence? provenance
Failure modes and hazards
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Civil tabulated date and locally sighted crescent disagree, so the same event is dated on different days in different countries.
- Confusion with Rabi' I (Rabi' al-Awwal) in records, especially abbreviated 'Rabi' without I/II.
- Software that assumes a fixed 30-day month or a fixed Gregorian mapping produces off-by-one or off-by-month errors.
- Historical documents using Rabi' al-Akhir vs Rabi' al-Thani can be misread as two different months.
- Which of these failure modes and hazards hold for the sense of Rabi II this model covers, and on what evidence? provenance
Regional variation
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Arabic: Rabi' al-Thani (ربيع الثاني) and Rabi' al-Akhir (ربيع الآخر) are both used; South Asian Urdu/Persian usage often prefers Rabi' al-Akhir / Rabi-us-Sani.
- English almanacs commonly write Rabi II, Rabi' II, or Rabi-ul-Akhir.
- Start date can differ by one day between Saudi Umm al-Qura, Pakistan/India sighting, and North African or Southeast Asian committees.
- Some popular commemorations attached to this month are regional (South Asia, parts of the Middle East) and are not uniformly observed.
- Which of these regional variation hold for the sense of Rabi II this model covers, and on what evidence? provenance
Neighbouring kinds and how to tell them apart
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Rabi' al-Awwal (Rabi I) - Rabi I is the third hijri month; Rabi II is the fourth. Test: ordinal position 3 vs 4, or Arabic awwal/thani (first/second).
- Jumada al-Ula (Jumada I) - Jumada I is the fifth month, immediately after Rabi II. Test: following month in the hijri sequence; name contains Jumada not Rabi'.
- Gregorian April or any fixed solar month - Rabi II is lunar and walks through the solar year. Test: it does not stay aligned with a named Gregorian month.
- Rabia as a personal name - Homophone/orthographic overlap only. Test: calendar context (AH year + day) vs anthroponym.
- Which of these neighbouring kinds and how to tell them apart hold for the sense of Rabi II this model covers, and on what evidence? provenance
Sources
- Rabi' al-Thani - Name variants, position as fourth hijri month, 29/30-day length, and that it is not a month of obligatory fasting or hajj.
- Islamic calendar - Lunar month structure, crescent-sighting versus tabulated civil calendars, and the twelve-month hijri sequence that places Rabi' al-Thani fourth.
- Rabi' al-Thani / Rabi' al-Akhir - Civil usage of the month name, typical length, and correspondence to shifting Gregorian dates.
What the second pass must settle
- Does the registry intend the recurring fourth Hijri month exclusively, or also historically distinct uses of the same month name?
- Which regional names and transliterations should be recognised automatically, and which require contextual disambiguation?
- Which calendar methods, issuers and historical periods must the first implementation support?
- What rule should select a calendar authority when the user's community or jurisdiction is unspecified?
- Does an existing Vercy calendar or world model already own Rabi II's identity or occurrence logic, requiring a link instead of duplicate ownership?