About Hilal Vision
رؤية الهلال — Connecting Ancient Tradition with Modern Astronomy
Last updated: October 2026 · Version: 2.1
Overview
Hilal Vision is a precision astronomical platform purpose-built to predict and visualise the visibility of the Islamic crescent moon (هلال — hilāl) at any location on Earth. It serves 1.8 billion Muslims who rely on lunar reckoning for the commencement of Ramadan, Eid al-Fitr, Eid al-Adha, and every new Hijri month, as well as researchers, astronomers, and Islamic calendar scholars who study crescent observation methodology.
The platform synthesises three decades of peer-reviewed crescent visibility research — principally the Yallop (1997) and Odeh (2004) criteria — with real-time ephemeris data, live cloud-cover overlays, and a validated historical observation archive from the Islamic Crescents' Observation Project (ICOP), to produce visibility forecasts that are both scientifically rigorous and immediately accessible.
Mission
The Islamic lunar calendar is one of humanity's oldest living scientific traditions. For over 1,400 years, the commencement of each sacred month has been determined by the physical sighting of the new crescent moon. In the modern world, however, this practice is fragmented: different countries announce the beginning of Ramadan on different days, communities lack transparent data-driven tools, and the gap between astronomical possibility and religious authority creates avoidable confusion.
Hilal Vision exists to answer a single question with the precision it deserves:
"Will the new crescent moon be visible tonight from my location — and why?"
We implement the internationally recognised Yallop (1997) and Odeh (2004) visibility criteria — the same standards used by Islamic calendar authorities in the United Kingdom, Malaysia, Morocco, and the International Astronomical Center — and present the results with the visual clarity and interactivity expected by a 21st-century audience.
This platform is not a religious authority. It is a scientific instrument. It presents mathematical predictions, historical data, and comparative calendar analysis side-by-side, empowering individuals and communities to engage critically and transparently with Islamic timekeeping.
Who Is Hilal Vision For?
Muslim Communities
Get clear, location-specific predictions for crescent visibility before Ramadan, Eid, and every new Hijri month — without jargon or ambiguity. Understand why your local authority may announce a different date from a neighbouring country.
Astronomers & Researchers
Access raw q-values, ARCV/DAZ parameters, Odeh V-values, and the full ICOP historical dataset (1438–1465 AH, 1,000+ observations) for validation and academic research. Export data in CSV or JSON.
Islamic Calendar Scholars
Compare Astronomical (computed), Umm al-Qura (KACST), and Tabular Hijri calendars side-by-side. Understand precisely where and why civil calendars diverge from physical astronomical sighting.
Educators & Science Communicators
Use the 3D globe, 2D visibility heatmaps, and horizon simulator as pedagogical tools to explain the mechanics of crescent visibility to students.
Platform Overview
Hilal Vision is organised into six specialised astronomical tools:
| Tool | Description |
|---|---|
| 3D Globe & 2D Visibility Map | Interactive WebGL globe and MapLibre 2D map rendering crescent visibility zones worldwide using Yallop/Odeh q-values. Includes real-time cloud cover overlay and Best-Time-to-Observe engine. |
| Moon Phase Dashboard | Current lunar phase, illumination percentage, lunar age, topocentric coordinates, altitude/azimuth charts, 30-day phase strip, and Yallop/Danjon methodology charts. |
| Hijri Calendar | Three-engine calendar (Astronomical, Umm al-Qura, Tabular) with Gregorian cross-referencing, Islamic events, and a "Compare with Sky" layer. |
| Local Horizon View | Local horizon simulator showing crescent and solar positions at sunset, annotated with ARCV, DAZ, elongation and Yallop q-value, plus sunrise, sunset, moonrise and moonset over the real skyline of your place (hills and mountains from public elevation data) and a check of whether the Moon is above the terrain when the Sun disappears. |
| ICOP Archive | 1,028 crescent observations from the Islamic Crescents' Observation Project for Ramadan and Shawwal 1440–1446 AH, set against the computed visibility for each month (1438–1465 AH). |
| Eclipse Tracker | Upcoming lunar and solar eclipses with a page for each one: local times, how much you will see from your location (including whether nearby terrain hides it), the path of totality or annularity on a map, optional eclipse alerts and a Pro simulator of the view. |
Technology Stack
Hilal Vision is built on modern, performant web infrastructure:
| Technology | Role |
|---|---|
| React 19 + Next.js 15 (App Router) | Core framework and server components |
| Globe.gl + MapLibre GL | 3D WebGL globe and 2D interactive map |
| astronomy-engine (Don Cross) | VSOP87/ELP2000 planetary & lunar position algorithms |
| tRPC + Drizzle ORM + PostgreSQL | Type-safe API layer and relational database |
| Clerk Auth | Authentication and user management |
| Capacitor.js and Trusted Web Activity | Native iOS and Android app packaging (in preparation) |
| react-i18next | 8-language internationalisation (EN, AR, UR, ID, MS, BN, FA, TR) |
| Serwist + PWA manifest | Offline-first service worker, push notification support |
| Open-Meteo API | Real-time cloud cover and atmospheric data |
| Upstash Redis | Rate limiting and caching |
| AWS Open Data Terrain Tiles | Public terrain elevation for the local horizon feature |
| Stripe + RevenueCat | Payment processing (web and native) |
| Vercel | Global edge hosting and analytics |
Scientific Methodology Summary
Crescent visibility prediction is a multi-variable problem combining:
- Topocentric ephemeris — precise Moon and Sun positions (altitude, azimuth, elongation) computed at the observer's geographic coordinates using VSOP87/ELP2000 algorithms at local sunset
- Crescent width (W) — topocentric crescent width in arcminutes derived from the Moon's angular diameter and elongation
- Arc of Vision (ARCV) — the vertical angular separation between Moon and Sun at local sunset
- Yallop q-value — a composite visibility statistic mapping ARCV and W to six visibility zones (A–F)
- Odeh V-value — an independent visibility statistic derived from 737 observations (almost half of them from ICOP), refining the Yallop model for telescopic and CCD sightings
- Danjon limit — the elongation below which no crescent has been seen with the naked eye, commonly quoted at about 7° (estimates range from about 5° to 7.5°); only specialised stacked imaging has recorded thinner crescents
- Atmospheric refraction — Bennett correction, scaled for local pressure and temperature, applied to apparent altitude
- Cloud cover — live Open-Meteo data displayed as an overlay; atmospheric overrides (temperature, pressure) allow expert adjustment of refraction models
See the Methodology page for the full mathematical derivations and algorithm documentation.
Comparison with Existing Tools
| Feature | Hilal Vision | Moonsighting.com | IslamicFinder | HilalMap |
|---|---|---|---|---|
| Interactive 3D Globe | ✓ | — | — | — |
| 2D Global Visibility Map | ✓ | ✓ | — | ✓ |
| Live Cloud Cover Overlay | ✓ | — | — | — |
| Best-Time-to-Observe Engine | ✓ | — | — | — |
| Real ICOP Observation Archive | ✓ | ✓ | — | — |
| Crowdsourced Sighting Reports | ✓ | — | — | — |
| Three-Engine Hijri Calendar | ✓ | — | — | — |
| Scientific Parameters (q/V) | ✓ | ✓ | — | — |
| Multilingual (8 languages) | ✓ | — | ✓ | — |
| Animated Timeline | ✓ | — | — | — |
Table reflects publicly available features as of March 2026. ✓ = available, — = not available.
Data Sources & Attribution
Hilal Vision stands on decades of peer-reviewed astronomical research. All data sources and their contributions are fully disclosed:
Yallop (1997) Visibility Criterion
B.D. Yallop, HM Nautical Almanac Office, Royal Greenwich Observatory.
"A Method for Predicting the First Sighting of the New Crescent Moon."
Technical Note No. 69, 1997. PDF
→ Provides the q-value formula and six-zone classification system underpinning all Hilal Vision visibility maps.
Odeh (2004) Visibility Criterion
Mohammad Sh. Odeh, International Astronomical Center, Abu Dhabi.
"New Criterion for Lunar Crescent Visibility."
Experimental Astronomy, vol. 18, pp. 39–64, 2004. ResearchGate
→ Provides the V-value formula, trained on 737 observations (almost half from ICOP) covering visual, binocular, and CCD/telescope sightings.
Islamic Crescents' Observation Project (ICOP)
International Astronomical Center, Abu Dhabi.
→ Historical archive of 1,000+ verified crescent sighting observations spanning 1438–1465 AH, used in the ICOP Archive tool and for calibrating the Odeh V-value model.
ICOP Database
astronomy-engine (Don Cross)
Open-source VSOP87/ELP2000 planetary position library for JavaScript.
→ Used for all topocentric Moon/Sun position computations, providing sub-arcsecond accuracy.
GitHub · MIT License
Umm al-Qura Calendar (@umalqura/core)
KACST pre-computed tabular calendar for Saudi Arabia's official civil Hijri calendar.
npm
Open-Meteo
Free, open-source weather API providing real-time cloud cover data.
open-meteo.com
AWS Open Data Terrain Tiles
Public elevation tiles (compiled from SRTM, Copernicus and other sources) used to work out the terrain skyline around a place for the local horizon feature. registry.opendata.aws/terrain-tiles
Natural Earth
Public-domain 110 m land and country outlines, used for the world maps in the blog. naturalearthdata.com
Meeus, J. (1998) — Astronomical Algorithms
Standard reference for atmospheric refraction correction formulas (Bennett correction).
Intellectual Property & Licensing
Hilal Vision is proprietary software. The brand, UI design system, code architecture, and proprietary data processing algorithms are the exclusive property of Athrwise Ltd.
- You may not copy, modify, distribute, reverse engineer, or sublicense any part of this platform.
- Third-party libraries (astronomy-engine, MapLibre GL, Drizzle ORM, etc.) are used under their respective open-source licences (MIT, Apache 2.0). Attribution is provided above.
- ICOP data is used with attribution to the International Astronomical Center.
- Yallop and Odeh criteria are published scientific formulas in the public domain; their implementation in Hilal Vision is original.
See LICENSE in the repository root for the full proprietary licence text.
Contact & Feedback
Found a bug, have a question about methodology, or want to contribute observation data?
- Contact page: moonsighting.live/contact
- Email: support@moonsighting.live
We welcome feedback from the astronomical and Islamic scholarly community.