Q. From Awny Al-Omari, Wisconsin, USA, 25 January 1996:
If the Ahmadiyyas maintain that a solar eclipse can sometimes occur on the 27th of a lunar month, then presumably a lunar one should be feasible on the 12th? However, they regard the 13th as the earliest possible day.
A. It is actually difficult to see how a solar eclipse could be witnessed as early as the 27th (see separate file). A sighting at dusk next day would terminate the month incorrectly after just 28 days. Of course they could postulate hazy conditions at the beginning and end of the Islamic month - thereby delaying the identification of the crescent (at a location specifically selected for their purpose).
Indeed, atmospheric visibility is one of the parameters they are prepared to vary, when it suits them. In particular, they need to assume that the Ramadan crescent was not seen from Qadian (near Lahore) on 8th March 1894. Only by postponing the start of the Holy Month, were they able to regard the date of the lunar eclipse as 13th Ramadan. However, it is likely that the New Moon would have been spotted on 8th March from places at higher altitude to the north or east, where the air was thinner, cleaner and drier.
Naturally, the Ahmadiyyas do need to be consistent with their criteria. And with the right combination of cir*****stances, there will then be situations which result in lunar eclipses occurring even earlier - on the 12th of an Islamic month.
This will happen at locations (i) where thick haze delays the beginning of the month by an extra day or two, (ii) where the inclination of the ecliptic is unfavourable for moonsighting, and (iii) whenever the interval between New and Full Moon is less than 14 days; (this is not at all uncommon: see the histogram in question 2 above).
For example, poor atmospheric visibility would also have obscured the Ramadan crescent on 8th March 1894 at latitude 40 South, longitude 120 West. If based on observations made just at that point, the new month would then have had to wait till the evening of the 9th. And the subsequent lunar eclipse on 21st March would have been in the early hours of the morning - which at that particular place was still the 12th of Ramadan.
So as you suggest, the 12th (not the 13th) is the first date when lunar eclipses can be witnessed (using criteria which the Qadianis themselves have adopted - but which can cause problems - see question 16). Thus, their March 1894 lunar eclipse did not occur on the earliest day possible. [See item 18 in this file].
Also refer to the article at http://www.dlmcn.com/qadfl.html
CALCULATIONS & REFERENCES
At dusk on 8th March 1894 at 40º South, 120º West, the base of the crescent was only 7.2º above the centre of the sun (ignoring refraction but allowing for parallax). Azimuth difference was 16.3º.
There are well-do*****ented cases where the moon was not visible under similar cir*****stances:
"Visibility of the lunar crescent" by B.E. Schaefer (1988). Q.J.R. Astron. Soc., 29, 511-523. (See observations 16, 22, 28, 99 and 100 in his Table I).
"Lunar crescent visibility" by B.E. Schaefer (1996). Q.J.R. Astron. Soc., 37, 759-768. (See his Figure 3).
"Limiting altitude separation in the New Moon's first visibility criterion" by M. Ilyas (1988). Astron. Astropys. 206, 133-135. (See his Figures 1, 2, 3 and 5).
However, if someone feels that the New Moon would probably have been visible on 8th March 1894 at 40º South, 120º West (even in hazy conditions), then we could recalculate for an observation point slightly further poleward - say at 45º South, 120º West - where it will be much harder to spot the crescent.
In addition, lunar latitude on 8th March 1894 was only -0.3º, so it could easily have been more unfavourable. For instance, on 8th February 2008, lunar latitude will be almost +1.0º, and at the beginning of nautical twilight (at 42º South, 50º East, say) the crescent will be extremely close to the horizon - impossible to see even in moderate haze. A locally determined new month at that particular place will have to wait till the evening of 9th February. Thus, the subsequent lunar eclipse on 21st February 2008 will be observed there (before dawn) on the 12th of the month.
October 1986 provides a similar illustration, this time from the northern hemisphere.
Dr. David McNaughton