They decide when Ramadan is by looking for the new crescent moon and, in some places, by using precise astronomical calculations to know when that moon should be visible.

The basic rule in Islam

In Islamic law, Ramadan starts when the new crescent moon (hilal) of the 9th lunar month is seen in the sky after sunset.

  • On the 29th day of Sha‘ban (the month before Ramadan), observers go out after sunset and look toward the western horizon for the thin crescent.
  • If it is seen , the next day is the first of Ramadan.
  • If it is not seen because the moon is not yet above the visibility limit or because of clouds, dust, or haze, then Sha‘ban is completed as 30 days, and after that Ramadan automatically begins.

This comes from prophetic sayings that tell Muslims to start and end fasting by sighting the moon or completing 30 days of the month.

Who actually decides?

In practice, it is not random people on their own; there is usually some organized authority.

  • In many Muslim‑majority countries (for example, in parts of the Middle East), official moon‑sighting committees or religious councils are appointed by the government to look for the crescent.
  • Trusted witnesses report a sighting; a judge or national council checks the report and then announces the start of Ramadan to the public.
  • Traditionally, witnesses must be considered upright and reliable; some classical jurists even listed conditions like being Muslim, sane, and known for honesty.

Because of this, you may see news headlines like “Moon‑sighting committee announces start of Ramadan” every year.

Moon sighting vs calculations (why dates differ)

Today there are two main approaches, and that is why sometimes Ramadan starts on slightly different days between countries or even mosques.

  1. Local naked‑eye/optical sighting (traditional)
 * People go out and try to see the crescent with the eye, binoculars, or telescopes.
 * The start of Ramadan depends on whether it is actually seen in that region.
 * Weather, light pollution, and human mistakes (e.g., confusing Venus for the moon) can cause disagreements or false announcements.
  1. Astronomical calculations (modern)
 * Astronomers can calculate exactly when the new moon is born and when it should be physically visible from different places on Earth.
 * Some councils use these calculations to **pre‑announce** the start date years in advance, arguing that science removes confusion and last‑minute uncertainty.

 * Other scholars reject relying purely on calculations, saying the religious texts only mention actual sighting or completing 30 days.

Because of these two methods, one country might start Ramadan on a Wednesday while another starts on Thursday, even though they are both following Islamic principles as they understand them.

Why the moon and not the sun?

Ramadan follows the Islamic lunar calendar , which is about 10–11 days shorter than the solar year.

  • The Quran mentions the phases of the moon as a way for humans to measure time and mark religious periods.
  • A lunar month begins when the new crescent becomes visible, so every Islamic month—including Ramadan—starts with that sighting.
  • Because the lunar year is shorter, Ramadan moves through all four seasons over a cycle of about 33 years.

So when you hear people say “they’re waiting for the moon” to know when Ramadan starts, it literally means they are waiting to confirm that tiny first crescent in the sky—or to confirm via agreed‑upon astronomical criteria that it would be visible.

Information gathered from public forums or data available on the internet and portrayed here.