Getting Started

Moon Visibility Explorer is designed to be intuitive and easy to use. Whether you are a first-time visitor or an experienced astronomer, this guide will help you understand all the features available to you. The tool operates entirely in your web browser — no downloads, installations, or accounts are needed.

Step 1: Reading the Visibility Map

When you first load Moon Visibility Explorer, you will see a global map with a control panel above it. The map displays the predicted crescent moon visibility for the selected date across the entire world. Each colored rectangle on the map represents a 2°×2° grid cell (approximately 222 km × 222 km at the equator), and its color indicates the predicted visibility classification.

Here is what each color represents:

Step 2: Selecting a Reference Date

The Reference Date picker in the control panel lets you choose which evening to analyze. The label "Evening of" reminds you that in the Islamic calendar tradition, the day begins at sunset — so selecting April 15 means you are asking about the visibility of the crescent moon on the evening of April 15 (after sunset).

The date you choose is typically the 29th day of the current Islamic month. If the crescent is visible on this evening, the new month begins. If it is not visible, the current month is extended to 30 days, and the new month begins the following evening.

After selecting a date, click the "Calculate Visibility" button. The calculation takes approximately 3-10 seconds as the tool computes the sun and moon positions for all 16,200 grid cells on the planet. A progress bar will show you the computation status.

Step 3: Selecting a City

The City dropdown is optional but recommended. When you select a city, the map will highlight its position with a distinctive marker, and the legend will display the specific visibility classification and sunset time for that city's coordinates.

Selecting a city also unlocks the "Calculate Lunar Calendar" button, which generates a full year's worth of Hijri month predictions specifically for that location. The tool currently supports over 70 major cities across the Middle East, South Asia, Southeast Asia, East Asia, Europe, Africa, the Americas, and Oceania — covering the vast majority of the world's Muslim population centers.

Step 4: Generating a Lunar Calendar

The Lunar Calendar feature is one of the most powerful tools in Moon Visibility Explorer. After selecting both a date and a city, clicking "Calculate Lunar Calendar" opens a modal that predicts the start of each of the next 12 Islamic months.

For each month, the calendar shows:

1. Islamic Month Name: The name of the Hijri month (e.g., Ramadan, Shawwal, Dhul Hijjah) along with the Hijri year.
2. Night 1 Date: The Gregorian date of the first evening of the month — i.e., the evening when the crescent is first visible (or inherited via shared night). Clicking "Night 1" will jump the main map to that date so you can see the global visibility for that specific evening.
3. Detection Method: Whether the month start was determined by direct visibility at the city's location, or via shared night inheritance from another region.
4. Visibility Classification: The Odeh V-criterion zone (EV, VP, VO) for your city on Night 1.

Understanding Shared Night (Ishtirak al-Layl)

Shared Night (اشتراك الليل) is a concept from Islamic jurisprudence (fiqh) that addresses the question: if the crescent is sighted in one location, does it also count for other locations?

The principle is that if two locations "share the night" — meaning their nighttime hours overlap — then a sighting in one location can establish the new month for the other. For example, if the crescent is easily visible in Casablanca, Morocco at sunset, and at that same moment it is already nighttime in Mecca, Saudi Arabia, then Mecca may adopt the Casablanca sighting since both cities share a portion of the night.

Moon Visibility Explorer implements this concept computationally. For each city, the tool checks whether any grid cells where the crescent is classified as "Easily Visible" or "Visible under Perfect Conditions" share nighttime hours with the target city. If such cells are found, the calendar marks the month start as "Shared Night" and identifies the source region. When viewing Night 1 on the map, cells that contributed to the shared night inheritance are highlighted in orange, making it easy to understand why the month started on that date even though the crescent was not directly visible locally.

Note: Different Islamic scholars have varying opinions on the shared night principle. Some require physical sighting within the same geographic region, while others accept sightings from anywhere that shares the night. Moon Visibility Explorer provides the astronomical data — the religious interpretation is left to qualified scholars and the user's own community.

Step 5: Exporting Your Calendar

After generating a lunar calendar, you can export it in multiple formats for personal use, printing, or sharing with your community:

• PDF Export: Creates a well-formatted document with all month start dates, visibility classifications, and supporting information. This is ideal for printing and distributing to mosque communities or Islamic centers.
• Google Calendar / ICS: Generates calendar events that can be imported directly into Google Calendar, Apple Calendar, or Microsoft Outlook. Each month's start is added as an event with details about the visibility conditions.
• CSV Data: For researchers and data analysts, the raw calendar data can be downloaded in comma-separated values format, compatible with Excel, Google Sheets, and other spreadsheet software.

Tips for Successful Moon Sighting

1. Check the weather forecast. Even if the Odeh criterion predicts "Easily Visible," clouds on the western horizon will prevent sighting. Plan to observe from a location with a clear view of the western sky.
2. Arrive early. Be at your observation point at least 15-20 minutes before sunset so your eyes can adjust and you know exactly where the sun will set.
3. Look in the right direction. The crescent moon will be near the point where the sun has just set — slightly to the left (south) in the northern hemisphere.
4. Use binoculars if available. Even if naked-eye sighting is expected, binoculars can help you locate the crescent faster. Once found with binoculars, you can often then see it with the naked eye.
5. Be aware of the time window. You typically have only 20-40 minutes between sunset and moonset to spot the crescent. It will be very faint at first and gradually become more visible as the sky darkens.
6. Avoid light pollution. Higher altitudes and locations away from city lights improve your chances significantly.

نصائح لرؤية ناجحة للهلال: تحقق من توقعات الطقس، اصل مبكراً قبل الغروب بـ 15-20 دقيقة، انظر في الاتجاه الصحيح بالقرب من نقطة الغروب، استخدم المنظار إن أمكن، وتجنب التلوث الضوئي.