The Holy Month of Ramadan 1311 (March/April 1894) contained both a lunar and a solar eclipse. The Ahmadiyya community attaches great importance to them, believing that they conferred unusual and special status on their leader, Mirza Ghulam Ahmed1.
Fundamental to their thesis is a claim that the lunar eclipse occurred
on the earliest possible date in an Islamic month - which they argue is
the 13th. For them, it was also significant that (according to their reckoning)
the subsequent solar eclipse took place on 28th Ramadan, supposedly occupying
the 'middle' of the permissible range of dates2.
Question-marks against eclipses on the 27th
The Ahmadiyyas maintain that a solar eclipse may be witnessed either during the 27th, or on the 28th, or on the 29th of a lunar month. At first glance the 27th does seem questionable, because a crescent sighting on the following date would terminate the month incorrectly after just 28 days. Remembering that a New Moon is born during a solar eclipse, its age just after sunset next day would exceed 24 hours - almost certainly rendering it visible somewhere in the world.
Admittedly, if people are following an Islamic calendar based on observations made just at one point, then even a 30-hour crescent will sometimes be missed, particularly if the sun-moon azimuth difference is quite great. (Under these circumstances, incidentally, reports from the opposite hemisphere3 are usually positive).
However, by referring back to the beginning of the month, we notice a larger obstacle confronting eclipses on the 27th.
For the illustration in Figure 1, a lunation of 29.4 days was adopted4 - less than the mean value of 29.53 days. Figure 1 uses a solar eclipse time near the end of the 27th day - with conjunction occurring 26.9 days after the commencement of the Islamic month. Subtracting that from 29.4 yields a 2½-day interval between the previous New Moon's birth and the onset of the month concerned (which is at sunset, as is customary). To make that possible, the crescent would have had to be invisible 24 hours earlier, i.e. approximately 1½ days after its conjunction (see Figure 1).
This could happen at a time and place with a comparatively shallow angle
between the ecliptic and the horizon5, although it will probably
need the additional handicap of poor atmospheric visibility.
Postponements due to haze - and the associated 28-day problem
Local haze is indeed a factor sometimes invoked by the Ahmadiyyas when determining Islamic dates. The prime example of that, involved postponing the start of Ramadan 1311 to the evening of March 9th, because the crescent was not visible from Qadian (near Lahore) on the 8th. This meant that the date of the subsequent Full Moon and lunar eclipse (21st March) became 13th Ramadan rather than the 14th, in accordance with the Ahmadi requirement.
At Qadian on 8th March 1894, vertical separation between the centre of the sun and the base of the crescent at dusk measured 10 degrees (allowing for parallax but without refraction). This placed the moon in the grey area between a positive sighting and a failure. However, the crescent would probably have been observed from high-altitude stations to the north or east of Qadian - where the air tends to be thinner, less dusty, and drier.
At Qadian, it would have been sounder to commence Ramadan 1311 on 8th March. Whenever haze prevents identification of a New Moon, as a general rule it is advisable to inquire whether it was detected elsewhere, and if so, to begin the new month immediately. This is because the sky could become quite clean at the end of the same month, revealing the crescent perhaps only 16 to 20 hours after conjunction. And if the first day of that month had been 'lost', it might then have to finish incorrectly after just 28 days. Two (or even three) successive 29-day months can occur naturally: in those circumstances the 28-day anomaly is possible with the later one - if its start is postponed due to local bad weather.
Dhu al-Hijjah 1411 (13th June to 12th July 1991) at 25º South,
65º East - provides a specific example of that problem, as discussed
in URL http://www.dlmcn.com/questions9q.html#q16
Lunar eclipses on the 12th of a month
Rules for determining Islamic calendars vary according to community and nationality; one cannot be dogmatic as to whether any particular system is "right" or "wrong". However, it is essential to be consistent - always retaining exactly the same criteria through the entire year (otherwise 28-day and 31-day months will occasionally be experienced).
If the Ahmadiyyas wish to base their decisions on observations made just at a specified point (like Qadian, where haze may hide a young moon), then lunar eclipses will sometimes be witnessed on the 12th of an Islamic month. This is because crescent identification is occasionally impossible even after 1½ days (as in Figure 1), and also because the interval between New and Full Moon can be less than 14 days.
The distribution of possible values of that interval6 is depicted in Figure 2. Short intervals occur when lunar perigee falls close to the moon's First Quarter; long intervals straddle the apogee. Fluctuation between the two extremes follows a 412-day cycle7 - which is about 14 lunar months. (That is the average time taken for the perigee point to complete a full circuit, i.e. migrating from New to Full Moon, and back to New Moon).
Here is an illustration of a late start to an Islamic month resulting in an eclipse falling on its 12th day. At the beginning of nautical twilight on 8th February 2008 at 42º South, 50º East, the crescent was quite close to the horizon - very difficult to see, (impossible in hazy conditions). A locally determined new month at this particular place (at sea level) would probably not have commenced until the evening of 9th February. In that case, the subsequent lunar eclipse on 21st February 2008 would have been observed there (before dawn) on the 12th of the Islamic month. These dates could well have prevailed even at 38º South; the haze on 8th February just needed to be slightly thicker.
Poor atmospheric visibility would also have obscured the Ahmadi Ramadan crescent on 8th March 1894 at 40º South, 120º West. If based on observations made just at this point, the new month would then have had to wait till the evening of the 9th - as at Qadian. In the southeast Pacific, however, the subsequent lunar eclipse on 21st March would have been witnessed in the early hours of the morning - which in that region was still 12th Ramadan. (Less haze would be necessary for a postponement to March 9th if we moved slightly further away from the equator, say to 45º South, 120º West).
There are well-documented instances in the past, when the lunar crescent remained hidden in haze with a sun-moon separation and configuration similar to these examples8.
Weather conditions favouring lunar eclipses on the 12th are not too different from those necessary to obtain solar eclipses on the 27th of an Islamic month (Figure 1), namely haze which is dense enough to disguise a 1½-day crescent.
Thus, the Ahmadiyyas must either accept that eclipses may occur on the
12th of a lunar month as well as on the 27th - or else they must regard
eclipses as impossible on both those Islamic dates. Whichever choice is
made, requires revision of their thesis.
REFERENCES and NOTES
1. Ruhani Khaza'in 17 by Mirza Ghulam Ahmed (1984, orig. 1902); see page 132. See also 'Lunar and solar eclipses as signs of the promised Messiah' by Saleh M. Alladin (July 1987): Review of Religions 82(7). (The Ahmadiyya movement originated in what is now northern Pakistan).
2. The original hadith predicted the return of the Mahdi when a lunar eclipse occurs at the beginning of an Islamic month, followed by a solar one in the middle; (see Dar-e-Qatni 1, page 188). The Ahmadiyyas interpret those words to mean 'the beginning (and middle) of the possible range': see references in note 1. They maintain that lunar eclipses are theoretically feasible only between the 13th and 15th inclusive, with solar ones distributed among dates 27, 28 and 29. They therefore believe that (for the prediction to be fulfilled) the lunar eclipse should take place on the 13th (which is supposedly the first day in its 'range'), with the solar one on the 28th (the middle day in its range).
3. 'A universal Islamic calendar' by David L. McNaughton (Jan. 1997): Hamdard Islamicus XX(1), pages 77-85. Figures 1 to 4 show how changes in hemisphere can affect prospects for sighting a newborn crescent. Diagram corrections appeared in July 1997 in Hamdard Islamicus XX(3), page 101.
4. To try and make a 27th-day event look more feasible, people might be tempted to choose an example when the lunar orbit-time (length of month) is particularly short. However, in one respect that will be counterproductive - because New Moon occurs near perigee during such months: see 'How long is a lunar month?' by Ala'a H. Jawad (Nov. 1993): Sky & Telescope 86(5), pages 76-77. Those circumstances accelerate the moon's migration, making it more likely to be spotted 24 to 36 hours after its birth.
5. See note 3.
6. Data supplied by Ala'a H. Jawad of the Kuwaiti Amateur Astronomy Society.
7. The graph in Internet site http://dlmcn.com/questions9q.html#lm14 depicts what is essentially the same oscillation (apart from a phase-difference of a few days).
8. 'Visibility of the lunar crescent' by
Bradley E. Schaefer (1988):
Q.J.R. Astron. Soc. 29,
pages 511-523; (see observations 16, 22, 28, 99 and 100 in his Table I);
'Lunar crescent visibility' by Bradley E. Schaefer (1996): Q.J.R. Astron. Soc. 37, pages 759-768; (see his Figure 3);
'Limiting altitude separation in the New Moon's first visibility criterion' by Mohammad Ilyas (1988): Astron. Astropys. 206, pages 133-135; (see his Figures 1, 2, 3 and 5).
Correspondence (see items 18, 15, 2 and 16)
Islamic Astronomy Page