Our Mission

Moon Visibility Explorer is a free, open-access astronomical tool designed to serve Muslim communities, astronomers, researchers, and anyone interested in the lunar cycle. Our mission is to provide transparent, scientifically rigorous predictions for lunar crescent (hilal) visibility worldwide, empowering individuals and communities to make informed decisions about the Islamic (Hijri) calendar.

For over 1,400 years, the sighting of the crescent moon has marked the beginning of each Islamic month. Today, with modern astronomical knowledge, we can predict with remarkable accuracy where and when the crescent will be visible — bridging the gap between traditional observational practice and scientific computation. Moon Visibility Explorer makes these calculations accessible to everyone, not just professional astronomers.

The Odeh V-Criterion

At the heart of Moon Visibility Explorer is the Odeh V-criterion, a scientifically validated empirical model developed by Palestinian-Jordanian astronomer Mohammad Shawkat Odeh in 2004. The model is based on a rigorous analysis of 737 lunar crescent observation records — both positive sightings (crescent seen) and negative reports (crescent not seen) — collected from observers across diverse geographic locations and atmospheric conditions worldwide.

The Odeh criterion evaluates two critical astronomical parameters: the topocentric arc of vision (the angular height of the moon above the sun at sunset) and the topocentric crescent width (how thick the illuminated sliver of the moon appears). Together, these parameters determine whether the crescent has sufficient brightness and angular separation from the sun's glare to be detected by the human eye.

The criterion classifies visibility into four zones:

• Easily Visible (EV): The crescent is thick and bright enough to be seen with the naked eye, even under imperfect atmospheric conditions. Most observers will successfully spot the moon.
• Visible under Perfect Conditions (VP): Sighting is possible with the naked eye, but requires excellent atmospheric transparency, an unobstructed western horizon, and an experienced observer. Clear desert skies are ideal.
• Visible with Optical Aid (VO): The crescent is too thin or too low to be seen without magnification. Binoculars (7×50 or larger) or a telescope are required. Some moon sighting committees accept optical-aided reports.
• Not Visible / Impossible (NV): The moon is either below the horizon at sunset or so close to the sun that no sighting is possible by any means. The new month cannot begin based on this observation.

Features

The History of Lunar Crescent Observation

The practice of observing the new crescent moon dates back thousands of years and spans many civilizations. The ancient Babylonians tracked lunar cycles for agricultural and religious purposes as early as 500 BCE. In the Islamic tradition, crescent observation became a religiously significant practice following the Prophet Muhammad's instruction to sight the moon for determining the start of Ramadan and other months.

Throughout Islamic history, dedicated moon sighting committees (lajnat al-ru'yah) have been established in virtually every Muslim-majority country. Professional and amateur astronomers, muftis, and community leaders gather at elevated locations with clear western horizons on the evening of the 29th of each Islamic month to observe the sky. In the modern era, this traditional practice is increasingly supplemented by scientific prediction tools like Moon Visibility Explorer, which help sighting committees know in advance whether the crescent is likely to be visible from their location.

The development of mathematical visibility criteria — from the early work of Fotheringham (1910) and Maunder (1911), through Bruin (1977), Ilyas (1988), and Yallop (1997), to the current state-of-the-art Odeh criterion (2004) — represents over a century of scientific effort to quantify what was historically a purely observational practice.

Technology Stack

Moon Visibility Explorer is built using modern web technologies to ensure fast performance, reliability, and accessibility across all devices:

• React 19: The user interface is built with the latest version of React for component-based architecture and efficient rendering.
• D3.js: The interactive global map is rendered using D3's powerful geographic projection capabilities with Natural Earth coastline data.
• astronomy-engine: All astronomical ephemeris calculations (sun/moon positions, conjunction times, moonrise/moonset) are performed using this precise, open-source library.
• Web Workers: Heavy computation is offloaded to background threads so the UI remains responsive during the 16,200-cell global calculation.
• Vite: Lightning-fast build tooling for development and production bundling.

Contact Us

We welcome feedback, feature requests, bug reports, and collaboration inquiries. Whether you represent a moon sighting committee, an Islamic organization, or are an individual astronomer, we would love to hear from you.

Email: moonvisapp@gmail.com

نرحب بملاحظاتكم واقتراحاتكم واستفساراتكم. سواء كنتم تمثلون لجنة رؤية الهلال أو منظمة إسلامية أو فلكيين هواة، يسعدنا التواصل معكم.