Moon Sighting: How to Determine the Start of Ramadan

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Dabir Ahmad Bhatti, UK

Dabir Ahmad Bhatti is a long-serving member of the Moon Sighting Committee for the Ahmadiyya Muslim Community UK

The Moon – A Brief Introduction

Our moon orbits around the earth in about 27 days, and one complete revolution is by definition one lunar month. Ever since time immemorial, the moon has been a source of fascination for man. Primitive man began to understand the different phases of the moon, though they would not have understood for many centuries that moon light was a reflective light of the sun – a fact revealed by Allah more than 15 centuries ago!

Allah says:

‘He it is Who made the sun radiate a brilliant light and the moon reflect a lustre, and ordained for it stages, that you might know the number of years and the reckoning of time. Allah has not created this but in truth. He details the Signs for a people who have knowledge.’ (The Holy Qur’an, 10:6)

Scientists today hypothesise that the universe was created by a Big Bang and this is confirmed by the Holy Qur’an:

‘Do not the disbelievers see that the heavens and the earth were a closed-up mass, then We opened them out? And We made from water every living thing. Will they not then believe?’ (The Holy Qur’an, 21:31)

Further, the current hypothesis is that after initial Big Bang, as the earth cooled, at some stage it was struck by a large meteorite:

‘The Moon may have formed in the wake of a collision between an early proto-planet and an astronomical body called Theia.’ 

Some Interesting Moon Facts

• The moon was formed about 4.5 billion years ago when a large meteorite the size of Mars, struck the earth
• Like the earth has gravity, the moon also has a gravitational force. But its gravity pull is only about one sixth of the earth’s gravity. Still, with this weak gravity, the moon is able to exert enough force to cause the rise and fall of tides of oceans on earth.
• As the moon travels around the earth, it also rotates on its own axis. This phenomenon means that the same side of the moon always faces the earth and we never get to see the other side of the moon.
• It is now confirmed that there is water on the moon! ‘In 2020, data from NASA’s SOFIA mission confirmed water exists in the sunlit area of the lunar surface as molecules of H₂O embedded within, or perhaps sticking to the surface of, grains of lunar dust.’ 
• Sadly, the moon is moving away from us, and eventually the moon will break away from us and we will lose our only satellite.
• But not so sadly, its only moving about 3.78 cm per annum, meaning that it will take about 15 billion years before the moon is completely separated from the earth. The sun will be continue to shine for about 6 to 7 billion years, so the earth will be probably be ‘wrapped up’ well before we see the moon drift free off us!
• The moon is only 238,855 miles away from us. Compare this to the distance the sun is which 93 million miles away!
• If we were able to drive to the moon in a hypothetical car, it would take 166 days of continuous driving at a constant speed of 60 mph to reach the moon. 
• In comparison, our journey using the same hypothetical mode of transport would take 177 years of continuous driving to reach the sun!
• If the earth was a football, the moon would be a tennis ball
• The moon is 400 times smaller than the sun. 
• Also, the moon is 400 times closer to earth than the sun. 
• It is because of this incredible fact that the sun and moon appear to us to be of the same size from earth! Scientists say that this is a pure coincidence. Perhaps its, but it may also be that Allah Almighty designed this so as to use it as a sign for the second appearance of the Holy Prophet Muhammad (saw)!

The Lunar Calendar

‘They ask thee about the new moons. Say, “They are means for measuring time for the general good of mankind and for the Pilgrimage.”’  (The Holy Qur’an, 2:190)

‘The reckoning of months with Allah has been twelve months by Allah’s ordinance since the day when He created the heavens and the earth. Of these, four are sacred. That is the right creed.’ (The Holy Qur’an, 9:36)

Like the solar year the lunar year also has 12 months. These 12 months were established amongst the Arabs well before Islam, perhaps even way before Prophet Abraham (as) raised again the fallen relics of the the Holy Ka’bah (today the principal mosque of Islam located in Makkah). The 12 months are as follows:

Muharram, Safar, Rabi’ al-Awwal, Rabi’ al-Thani, Jumada al-Awwal, Jumada al-Thani, Rajab, Sha’ban, Ramadan, Shawwal, Dhu al-Qa’dah, and Dhu al-Hijjah

Of these 12 months, the following 4 months were sacred, and had been sacred for as long as the Arabs can remember, even before Islam: 

Dhu al-Qa’dah, Dhu al-Hijjah, Muharram, and Rajab

The Ka’bah had remained focal point since time immemorial, and the Arabs gained from the commerce as a result of the influx of foreign traders who would come to perform their religious rites during the holy month Dhu al-Hijjah. As the lunar month of Dhu all-Hijjah would lag behind the seasons, the Arabs had the practice of interpolation of inserting ‘false’ lunar months so that they could align the month of al-Hijjah with their season of harvest to gain maximum benefit from trade. This practice was banned by Allah:

‘Surely, the postponement of a Sacred Month is an addition to disbelief. Those who disbelieve are led astray thereby. They allow it one year and forbid it another year, that they may agree in the number of the months which Allah has made sacred and thus may make lawful what Allah has forbidden. The evil of their deeds is made to seem fair to them. And Allah guides not the disbelieving people.’ (The Holy Qur’an, 9:37)

The moon is our nearest neighbour and it travels in an ellipse around the earth. The direction of the travel is anti-clockwise. 

It travels in an ellipse around the earth. The nearest it gets to the earth is about 357,000km and the furthest is around 406,000Km

Why Does the Moon Have Different Shapes?

‘And for the moon We have appointed stages, till it becomes again like an old dry branch of a palm-tree’ (The Holy Qur’an, 36:40)

As the moon travels around the earth, the light of the sun that falls on the moon is reflected back to us. The part of the moon that is illuminated determines the shape of the moon. The earth itself is titled with respect to the sun, and the moon’s orbit around the earth is on a different plane to the earth’s orbit around the sun. 

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As can be seen, when the moon is directly in front of the sun, there is no light reaching the moon that is facing the earth. In this position it is impossible to see the moon. This by definition is known as the astronomical New Moon. As explained above, The moon itself does not have any inherent light. What we observe from earth is the reflected light of the sun.

As the moon continues to travel in its orbit, part of the moon begins to receive sunlight and we are able to see a portion of the sun’s light being reflected by the moon. 

As the moon moves away from the sun – the thin crescent begins to appear. The further it moves away, the bigger the crescent. It takes about 2 hours to move one degree. For visibility by the naked eye, the moon must move by at least 10 degrees.

Looking at the moon during its stages, one can see the earth’s circular shadow cast upon the moon.

The moon takes approximately 29.53 days (about 29 days and 13 hours) to complete one full orbit of the Earth. The lunar year is 354.4 days (6 months are 29 days and 6 months are 30 days) and is about 10 days shorter than the solar year. This is why we see Ramadan come forward by about 10 days each year. 

As the Moon travels in its 29.5 (or so) day orbit, its position changes daily. The Moon’s orbit sometimes takes it between the Earth and the Sun (known as New Moon or the Astronomical New Moon), sometimes opposite the Earth and Sun (known as ‘Full Moon’), and sometimes half way in between (known as ‘First-’ and ‘Third Quarter Moons’). The Moon does not itself produce any light but reflects the light radiated from the Sun. The different amounts of the Moon’s surface lit up by the Sun is seen from the Earth as lunar/Moon phases.

These phases of the Moon change throughout the month in a regular, predictable way. In fact, the phase of the Moon is correlated to its angular distance from the Sun, as seen from the Earth (known also as ‘angle of elongation’ or ‘angular separation’). 

The Crescent Moon is usually seen after sunset. As the Moon moves west from the point where the Crescent Moon is first visible on Earth, the crescent becomes thicker. Due to the elliptical orbit of the Moon, the first visibility starts from different locations on the Earth every month. Sometimes, it may start from the Southern hemisphere and sometimes from the Northern hemisphere. It may also start from any location from the east to the west.

The location of the first visibility of the Moon is not repeatable every year (like sunrise/sunset times) because the length of the lunar year (354.4 days) is shorter than the solar year (365.25 days). Hence, it takes approximately 33.5 years for the location of the first Crescent Moon visibility to repeat itself! The Moon can be seen at different positions in the sky, depending on where one observes from – in some locations it will appear higher above the horizon than others. And the path that it takes for moonrise (to go above the horizon) and moonset (to go below the horizon) are different depending on one’s location on Earth. In some locations it will seem like a slanting path while in others it will be more vertical.  

The distance of sun and moon from earth varies depending upon their positions in orbit. The sun is at an average distance of about 8.4 light minutes from earth. The moon is at an average distance of 1.38 light seconds (or 0.023 light minutes) from earth.

What is the New Moon?

When the moon is in line with the sun as shown in the picture above, it is in ‘Conjunction’, which is known as the birth of the new moon or the astronomical new moon. At conjunction, the moon is 0 degrees away from the sun. The Islamic month does not start at astronomical new moon. 

As early as Babylonian times, it was possible to calculate date and time of conjunction. Today, with modern astronomical calculations, conjunction can be calculated very precisely – to the second!

So the question is, why the uncertainty in the start of Ramadan and when Eid falls?

Determining the Start of Ramadan

The moon is used to determine the start of each lunar month. The Holy Prophet (sa) was aware of the neighbouring Jewish tribes, who also kept a lunar calendar. They were able to calculate with a good degree of accuracy, the birth of the new moon. 

Yet, the Holy Prophet Muhammad (sa) instructed the Muslims:

‘We are ummiyah (unlettered) people, we neither write nor calculate. The month is this way and that, sometimes 29 days and sometimes 30.’

And again, he said:

‘When you see the new moon, observe fast, and when you see it (again) then break it, and if the sky is cloudy for you, then complete thirty days for the month of Shaban’. (Bukhari and Muslim)              

It is upon these guiding principles enunciated by the Holy Prophet (sa) of seeing the crescent moon with the naked eye that lays the foundation for determining the start of each lunar month.

While conjunction or astronomical new moon can be calculated accurately, visibility of the new moon depends on a number of variable conditions and it can take from two to three days from the birth of the astronomical new moon to satisfy those conditions.

Early Crescent Visibility Criteria

Inspired by the guiding principles given by the Holy Prophet (sa), Arab Muslim astronomers embarked on the study of the heavens and began to postulate various theories to predict when the moon could be seen with the naked eye and thus determine the start of the next lunar month.

Several theories were presented by various scholars, amongst the eminent scientists were Al-Biruni (973-1048), Al-Qarafi (1228-1285), Ibn Taymiyyah (1263-1328), Al-Subki (1284-1355) to name a few. Whereas they could all predict accurately when the astronomical new moon was going to be born but predicting when it would be visible to the naked eye was an entirely different matter altogether. 

Crescent visibility by the naked eye is dependent on a number of factors resulting in a complex series of computations of the moon in relation to the sun, together with effects of varying and unpredictable atmospheric conditions.

While the Arab astronomers made impressive progress without the aid of modern technological instruments, it was later in the 19^th and 20^th centuries that scientists of western nations began to get involved.

One important discovery was made by a French astronomer by the name of André-Louis Danjon (6 April 1890 – 21 April 1967) who with extensive study using modern instruments available at the time, came to the conclusion that the moon would be impossible to see even with a telescope if the angle between the sun and the moon was less then 7.5 degrees. This angular separation of the sun and the moon is known as the elongation, and the limiting factor is now known as the Danjon limit. 

Today, the Danjon limit still exists, and plays a crucial part in any Crescent Visibility Criteria. The Danjon limit, with further ongoing study by other scientists, has been refined and the general acceptable Danjon limit today is 6.4 degrees. It is important to understand that the Danjon limit is just one of several criteria that forms part of any Crescent Visibility Criteria.

Present Crescent Moon Visibility Criteria

In 1998, Dr Bernard Yallop in his capacity as a lead for HM Nautical Alamanac Office at the Royal Greenwich Observatory, published a criterion based on around 300 sightings and non-sightings of the moon. His algorithm gave a quantitative value ‘q’ which was an indication of the probability of sighting the crescent moon. Using this value of ‘q’ he created the following 6 bands of visibility:

Using the Yallop’s Cresent Visibility Criteria, we can sum up broadly what is required for a positive visibility.

Crescent Visibility Requirements

1. Moon Age > 22 hours. The illumination of the moon by a single degree. Each degree corresponds to 2 hours of age
2. Elongation > 15 degrees. Elongation also depends on various factors – elongation at new moon, the speed of the moon, the distance of the moon from the earth, and the location of observer. 
3. Moon altitude > 4 degrees. 
4. Lag time > 12 minutes. Since the moon is moving eastward in its orbit around the Earth, the moon moves about 12 degrees in the sky each day and rises later each day – lagging behind the sun until eventually (at full moon) it rises at sunset and sets at sunrise.  
5. Moon set before sunset
6. Clear atmospheric conditions
7. The minimum elongation crescent seen by optical aid is 6.4 degrees 
8. For naked eye observations this minimum elongation is 7.7 degrees

FAQ

1. What does the term New Moon mean?

   New moon occurs when the moon completes its orbit around the earth and is in a position where it is in line with sun. This is known as ‘conjunction’ in astronomical terms. In this position no light of the sun is reflected back to us and the moon is completely hidden from view.

2. Why is Ramadan 29 days and sometimes 30 days?

   The Islamic calendar uses the lunar orbit to determine its months. The moon takes 29.53 days (approximate 29 days and 13 hours) to complete one full orbit of the Earth. The lunar year is 354.4 days (6 months are 29 days and 6 months are 30 days) and is 10 days shorter than the solar year. So, some months of the lunar year will be 30 days, and some months will be 29 days. Unlike the solar calendar, which has alternative 30 and 31 days (except for February), the lunar months are not fixed and do not necessarily follow a pre-determined pattern of 30 days and 29 days. Thus, Ramadan is 30 days long in some years, and 29 days long in other years
    

3. Once the new moon can be determined using astronomical calculations, why does its visibility vary each month?

   The visibility of the crescent moon is not a fixed period after new moon. There are several factors involved that determines when the new crescent can be seen or not and each month is different. Sometimes, the moon sets before the sun and cannot be seen. Sometimes the moon is on the horizon only briefly before disappearing below the horizon. Sometimes the moon is below the Danjon limit.

4. What is the Danjon Limit?

   The ‘Danjon Limit’ is the minimum angular separation between the Sun and Moon at which a lunar crescent can be seen by the naked eye, typically estimated to be around 7.5 degrees. When the angular separation, also known as the elongation, is below the Dajon limit, the moon is impossible to see even with a telescope. Typically elongation needs to be greater than 15 degrees for naked eye visibility, but this to is subject to other conditions also being favourable.

5. The new moon can be calculated accurately using astronomical calculations. Why don’t we start the lunar month with the new moon?

   Indeed, the new moon can be calculated accurately. According to the sunnah and hadith, Muslims will determine the start of a month when the crescent moon become visible. Hadhrat Umar (ra) reported that the Prophet صلى الله عليه وسلم said: ‘We are ummiyah (unlettered) people, we neither write nor calculate. The month is this way and that, sometimes 29 days and sometimes 30.’

6. Instead of using calculations, why don’t we use local sighting as per the Sunnah (practice of the Holy Prophet (sa)) and Hadith (sayings of the Holy Prophet (sa))?

   According to Hadith: ‘When you see the new moon, observe fast, and when you see it (again) then break it, and if the sky is cloudy for you, then complete thirty days for the month of Shaban’. (Bukhari and Muslim)’. In this country and generally in the western and northern countries, t he conditions are often cloudy and the moon will remain hidden behind the clouds. What can easily happen in is that we will end up with a series of 30-day months. Then, when at the beginning of a month on a clear day, we may see the moon on the 27^th night, making it a 28-day month! We cannot have a 28- or 31-day lunar month. To avoid this, we must use tools available to help us determine the start of a new lunar month. It is similar to determining the Iftari time or Maghrib time. We don’t go out to watch the sun set for Iftari, but rely on Salat Calendars which have been prepared using astronomical calculations.

7. Why do Muslims around the world have different start of Ramadan and Eid days?

   It is possible for a country west of us to see the crescent moon before us. For example, this year in 2025, North and South America and most of West Africa will be able to view the crescent moon on the 28^th February. Here in the UK, on 28^th February, the moon will only visible by using a telescope. 

8. Why do Muslims even in the same country have different days for start of Ramadan and Eid?

   The Ahmadiyya Muslim Community, by the Grace of Allah, is united by Khilafat (Caliphate) and his blessed guidance. We follow the crescent moon visibility local to our horizon. The Ahmadiyya Muslim Community in the UK obtains data from HM Royal Observatory Greenwich each year to determine Crescent Visibility for each month of the lunar year. The Yallop criteria was in fact developed by Yallop while working for the Royal Observatory and that data is still maintained by them.  Other Muslims will follow the crescent visibility horizon of the nearest Muslim country, in this case Morocco. It appears that in Morocco the crescent moon was seen with the unaided eye on 1^st March and therefore will start Ramadan on 2^nd March, which is the same for us in UK. There are other Muslims in the UK who follow the decisions made by Saudi Arabia who have announced the start of Ramadan to be a day earlier on 1^st March. Even though it is not possible to see the moon in Saudi Arabia with the unaided eye, it may be possible to see it using telescopes with some difficulty.

9. The moon on the evening of 1^st March in Islamabad, Tilford, UK looks like its more than 2 days old, how is this possible?

   This is because on the 28^th Feb at sunset, the moon was about 17 hours old and the elongation (separation from the sun) was 10 degrees. This makes it impossible to see the crescent with unaided eye. The following sunset, the moon is now 41 hours old and not only easily seen by the unaided eye, but also appears to be big. Sometimes, it is possible that a moon may set before the sun, and again sometimes, the moon is on the horizon only briefly before disappearing below the horizon

10. We can calculate the actual position of the moon, but when taking into account the different conditions required for crescent visibility, how do we calculate when the moon is going to be visible?

    This is a good question, and has been the subject of study for hundreds of years both by Muslim and non-Muslim astronomers. Over the centuries, several visibility criteria have been proposed. Among the Muslims the following are to name a few: Al-Biruni (973-1048), Al-Qarafi (1228-1285), Ibn Taymiyyah (1263-1328), Al-Subki (1284-1355) to name a few. As technology advanced, better criteria were proposed, and today a number of reliable criteria exist, like Odeh, Yallop, etc. The Ahmadiyya Muslim Community uses the Yallop criteria. 

11. What is the Yallop criteria?

    In essence, the Yallop criteria is ‘The translation of astronomical data to sighting possibly curves (commonly known as curves A,B,C,D, E & F) is based on probabilities and it is not absolute. It is an extremely good guide and as more date is collected and amalgamated into the scientific model, the (probability) based sighting curves will become even better.’ This means that Yallop used empirical data of past sightings and non sightings and plotted a graph which was used to predict the probability of sighting the crescent visibility with the unaided eye and with telescopes.

12. What happens if the Yallop criteria says the moon is not visible, but we later see the moon with the unaided eye?

    This is unlikely to happen, as astronomical technology has advanced. However, in the unlikely that it does happen, then local eye sighting will take precedence over calculations, and this is always the case.