Crescent Sighting 
Frequently Asked Questions

1. Are there some locations on the globe inherently better than others for sighting the new crescent?
2. Could you please clarify a notion that astronomy is forbidden in Islam?
3. Is it possible to see the moon near the sun in the morning and during sunset in the same day? And when does that happen
4. The Prophet (Peace be upon him) went to Arafat on Friday the 9th Dhu al Hijjah of 10 AH which was on March 6, 632 CE. Is it correct according to calculation? Give detailed answer with exact time?
5. If we go to higher altitudes like on top of a mountain or in an airplane, does it help for moonsighting?
6. Was astronomy relied upon thousands of years ago, especially when cloudy weather obstructed visual observation?
7. Is the calculation of solar movement more exact than the calculation of the lunar movement?
8. Is it possible to have several consecutive months of 29 days and to have several consecutive months of 30 days and what is the highest possible number?
9. What is The Astronomical New Moon? 
10. What is the relevance of Elongation in crescent sighting? 
11. What is the relevance of Sunset in crescent sighting?
12. What is the relevance of Moonset time in crescent sighting? 
13. Is there an accepted criterion for crescent sighting?
14. When has the earliest crescent of a new moon been seen after the moon was born? 
15. What is the process one must use to correctly sight the moon?
    
    
    

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1. Are there some locations on the globe inherently better than others for sighting the new crescent?
   
   YES. These are locations that have factors that are better for optics
   than other locations.
   
   Locations looking out over the ocean are better than those looking in the direction of a populated city.
   
   Poor air transparency due to molecules and dust suspended in the air is also bad for visibility. The air transparency is better for higher elevations like mountain tops.
   
   Urban and industrial areas are at a disadvantage compared with rural and more arid areas.
   
   The average cloud cover is significantly higher at high latitudes and near equator than in the subtropics and lower temperate zones.
   
   The haze effect also known as light extinction, dims the crescent by a large factor. At the low altitude where the most marginal crescents would be seen, only about 5% of the light from the crescent can penetrate the air, and 95 percent is lost because it is scattered away in other directions, even in the cleanest air.
   
   In a humid or polluted environment, much less than 1 percent of the light of a thin crescent comes to the earth.
   
   If the background light from the rest of the sky is brighter than the thin crescent, it would render the crescent invisible.
   
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2. Could you please clarify a notion that astronomy is forbidden in Islam?
   
   The notion that astronomy is prohibited in Islam is a misconception that emerged some 1200 years ago when Astrology and Astronomy were not considered separate science. Then Ilm-un-Nojoom was encompassing both astronomy and astrology. At that time Muslim Ulamaa said something like this that it is prohibited in Islam.
    
   Now it is clearly understood that Astrology is prohibited but Astronomy (Ilm-ul-falakyat) is not. Astronomy is the knowledge of movement and position of cosmos (heavenly bodies), while Astrology is the effect of position of those heavenly bodies on human beings' future. Future is not known to anyone except Allah subhaana wa Taala, so Astrology is considered "Haraam" in Islam.
   
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3. Is it possible to see the moon near the sun in the morning and during sunset in the same day? And when does that happen?
   
   No. But it is possible to see the Moon on one morning before sunrise in the East, and then on the next day's evening (i.e. after about 36 hours) it can be seen after sunset in the West. This happens very seldom for a specific location. Usually the Moon remains hidden for two days, a day before new moon, and a day after new moon.
   
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4. The Prophet (Peace be upon him) went to Arafat on Friday the 9th Dhu al Hijjah of 10 AH which was on March 6, 632 CE. Is it correct according to calculation? Give detailed answer with exact time?
   
   Very correct. The calculation confirms that new moon occurred at 21:07 GMT on February 25, 632 CE(Tuesday). On the following day, February 26, 632 CE in Medinah, the calculations for the moon show the following results:
   Sunset at 6:25 pm, moonset at 7:04 pm. At sunset, the elongation is 10.1, Age of moon 18.3 hours, and Altitude above horizon 7.6°.
   
   This crescent would have been visible on February 26, 632 CE(Wednesday), and the 1st of Dhu al Hijjah would have been on February 27, 632 CE(Thursday). Therefore the day of Arafat, 9th Dhu al Hijjah would have been on March 6, 632 CE(Friday).
   
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5. If we go to higher altitudes like on top of a mountain or in an airplane, does it help for moonsighting?
   
   Going to a higher elevation really does not change the situation except for a small time delay added to the setting times for sun and moon. This delay by itself helps very little. However, going to higher elevation helps the visibility, because the higher the elevation, the better is the air transparency, and the lower is the light extinction. But this does not mean that a moon of 10 hours old can be seen from high monutains or even from airplanes.
   
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6. Was astronomy relied upon thousands of years ago, especially when cloudy weather obstructed visual observation?
   
   Thousands of years ago, astronomy was not as accurate as it is today. 
   But then there were not many man-made objects in the sky either. Now a days people can see many man-made objects and think they saw the moon. We are trying to educate the people, so they understand the basic known facts about the moon, and when it is impossible to see. This way, when a Muslim or a group of Muslims see something and believe it to be the new crescent, we all can differentiate that it was not the crescent.
   
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7. Is the calculation of solar movement more exact than the calculation of the lunar movement?
   
   Calculation for the movement of the Moon is as accurate as that of the
   Sun. However, the Sun, being a source of light, can be seen easily, while the Moon, which does not have any light of its own, can only be seen when the Sun is in such a position that its light falling on the Moon can come to the earth.
   Many a time the Moon may be above horizon, but it cannot be seen because the Sun is in such a position that its rays coming to the Moon do not make a sufficient thickness of crescent to be seen from earth.
   
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8. Is it possible to have several consecutive months of 29 days and to have several consecutive months of 30 days and what is the highest possible number?
   
   Yes. According to calculations of moonsighting, and actually observed, up to three consecutive months of 29 days and up to four consecutive months of 30 days are possible. This is nothing unusual. This happens quite often.
   
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9. What is The Astronomical New Moon?
   
   The Astronomical New Moon, or the invisible New Moon, is the moment when the moon is almost directly between the earth and the sun. At this moment the moon's dark surface faces the earth. Therefore it is completely invisible even if it occurs in the middle of the night. The Astronomical New Moon occurs every 29 days, 12 hours, 44 minutes, and 2.8 seconds. The date and time of this invisible New Moon is commonly found in almanacs, newspapers and calendars.
   
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10. What is the relevance of Elongation in crescent sighting?
    
    Elongation is the angular distance between the moon and the sun. At The Astronomical New Moon this angle is zero and all the sunlight reflected by the moon surface is directed back towards the sun. With passage of time, the moon in its circular motion around the earth, moves away from the alignment with the earth and the sun. The angular distance between the moon and the sun increases, and some 18 to 24 hours after the Astronomical New Moon, the moon will have moved sufficiently for the sunlight reflected off its outer edge to be directed towards the earth. The new crescent moon can now become visible on earth.
    
    Elongation is a critical factor in determining the crescent's visibility, and this depends on more than just time. In the early 1930's, the French astronomer Andre' Danjon deduced (from detailed consideration of the geology of the Moon) that no illuminated portion of the crescent can be seen from the earth when the Moon is 7° or less from the Sun. No sighting can penetrate this barrier, which is set by shadows cast by the rough lunar terrain. This is the limit of our human observational power, and below this the crescent will be impossible to see, even with a telescope
    
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11. What is the relevance of Sunset in crescent sighting?
    
    In the first sixty hours or so after The Astronomical New Moon, the sunlight reflected by the moon is so weak that the crescent cannot be observed while the Sun is in the sky. Generally, for sighting the new crescent, one should start to search the sky about 15 minutes after sunset. One should look in the direction of the setting sun, just above, or upto 30 degrees to the right, or 30 degrees to the left of where the Sun set. One should keep looking until the time of moonset that can be obtained from local newspapers. Binoculars do help.
    
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12. What is the relevance of Moonset time in crescent sighting?
    
    Moonset time is the time when the upper limb of the Moon is on the horizon. If the sky is clear and the horizon is flat, crescent sighting should be possible some 15 minutes after sunset. Quite obviously there cannot be a crescent sighting if this is after the moonset time. The moonset time can be obtained from local newspapers.
    
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13. Is there an accepted criterion for crescent sighting?
    
    It is easy to design a criterion based on certain theories or confirmed sightings. But it is hard for that criterion to withstand the test of actual sighting. We have to be the judge and see if the criterion comes out true to the actual sighting month after month, and year after year. In our own community, records go back to 1932. Month after month, circulars detailing predictions have been regularly published, followed by notification of confirmed sightings. Our community has published calendars from different parts of the world, with remarkable accuracy. This includes the planner from the World Federation.
    
    With many years of experience, we have fine tuned our criteria of prediction, so that our calculations are borne out by observation time and again. Today our main criterion depends on the Moon's angular distance from the Sun at sunset (elongation) and the Moon's altitude (in degrees) above the horizon after sunset. The age of the Moon is recorded as a guideline.
    
    Elongation at sunset, the Moon / Sun angular separation, should be not less than 9.7°
    
    The Crescent must be well above the horizon when the sun has dropped 5° below the horizon.
    
    Crescent age at sunset is normally not less than 20 hours.
    
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14. When has the earliest crescent of a new moon been seen after the moon was born?
    
    Moon sighting does not depend on age. Non-Muslims have treated this question as a sport, who can see the youngest moon. In the zeal of their competition, they claim early and early sightings, which are in most cases false, as many claims have been refuted with no sighting at places thousands of miles west. The authentic sightings are at about 17.2 hours with the naked eye, and 15.5 hours by observatory telescopes. Remember, in some seasons, earliest moonsighting takes about 24 hours. So if the moon has become 17 hours old or more, one can not conclude that it is possible to see that moon.
    
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15. What is the process one must use to correctly sight the moon?
    
    If you know that the beginning of the month was based on an authentic cresent sighting, count 29 days from the start date and start looking about 15 minutes after sunset. Look in the direction where the sun set, just above, or upto 30 degrees to the right, or 30 degrees to the left. Keep looking until the time of moonset that you can obtain from local newspapers. Binoculars help. Have one or more persons with you, if possible. If you do this for a few months, you will know yourself about improving your procedure.
    You should keep in mind the distinction between occasions when the Crescent is "difficult but DEFINITELY and repeatedly seen", and occasions when the Crescent is "possibly fleetingly glimpsed but NOT DEFINITELY seen." For the former the Crescent should be continuously visible for at least five seconds in a sky location which is consistent from one minute to the next and the shape of the brightening should be consistent with the Moon-Sun angle. If in ANY doubt, accept that you haven't objectively seen the Crescent.
    
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