Introduction

I first presented software to find the best times for observing thin lunar cresents at the 7th NACAA in 1976  (Ref 1), but have never taken this further other than to attempt continuous observation of morning events due to a very favourable easterly outlook from my observatory.

A search of the internet for information on the best times to find and observe thin lunar crescents yielded a surprising result - software for the determination of Accurate Times and ephemerides for all TLCs (Ref 2).

This software meets the Moslem faith requirements in that the true date for the beginning of each calendar month is known as indicated by the first observable thin lunar crescent, or TLC. At this instant accurate times for prayer and the true location of Mecca can be deduced to meet Islamic rules.

Observation

Observation of a TLC at 6:15 am, summer time on the morning of 16 February 2007 some two days before new moon, revealed an easily observable crescent . The age of the TLC was estimated as -45 hours old.

Software results

The Accurate Times software was downloaded and run to compare with the above observation .
The results were extremely encouraging  giving a TLC geocentric age of -44h59m18s, almost exacltly equal to that observed.

The software results were as follows:

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                         By the Name of Allah
                   Jordanian Astronomical Society (JAS)
                   Accurate Times 5.1, By Mohammad Odeh

* Settings:-
- Calculations for Muharram 1428 AH Waning Crescent (Old, Morning).
- Crescent Visibility on: Friday  16/02/2007 CE
- Calculations are Done at User Time at:  05:15:00 LT
- Calculations are Geocentric.
- AUSTRALIA ACT Theodore, Long: 149:07:01.0, Lat: -35:27:05.0, Ele:704.0, Zone:10.00
- Summer time is: Off
- Height above mean sea-level affects rise and set events.
- Refraction Settings: Temperature: 10 °C   Pressure: 1010 mb
- Delta T: 65.02 Second(s)
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- G. Conjunction Time: 18/02/2007 CE, 02:14:18 LT
- Julian Date at Time of Calculations: 2454147.30208

- Moorise: 03:18:49 LT                    G. Moon Age:   -44H 59M 18S
- Sunrise: 05:31:57 LT                    Moon Lag Time: +02H 13M 08S

- G. Moon Right Ascension: +20H 18M 49S   G. Moon Declination: -23°:24':57"
- G. Sun Right Ascension:  +21H 55M 47S   G. Sun Declination:  -12°:36':28"

- G. Moon Longitude: +301°:34':17"        G. Moon Latitude: -03°:41':55"
- G. Sun Longitude:  +326°:43':21"        G. Sun Latitude:  -00°:00':00"

- G. Moon Altitude: +19°:59':47"          G. Moon Azimuth: +105°:04':21"
- G. Sun Altitude:  -05°:03':04"          G. Sun Azimuth:  +109°:23':09"

- G. Relative Altitude: +25°:02':51"      G. Elongation:  +25°:24':14"
- G. Relative Azimuth:  -04°:18':48"      G. Phase Angle: +154°:32':03"

- G. Crescent Width: +00°:01':34"         G. Moon Semi-Diameter:  +00°:16':05"
- G. Illumination:   04.86 %              G. Horizontal Parallax: +00°:59':02"

- G. Magnitude: -06.43                    G. Distance: 371470.78 Km

- According to Odeh Criteria, using the following values at Best Time:
  * Moon-Sun Topocentric Relative Altitude =+24°:11':51" (24.2°)
  * Topocentric Crescent width = +00°:01':30" (1.50')
  * q = 25.22

  * The Crescent Visibility is: Easily Visible By Naked Eye.

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* Remarks:-

- Date format: dd/mm/yyyy.
- The Prefix 'G.' means Geocentric, and 'T.' means Topocentric.
- For New Crescent: Moon Lag Time = Moonset - Sunset.
- For Old Crescent: Moon Lag Time = Sunrise - Moonrise.
- For New Crescent: Best Time = Sunset + 4/9 (Moon Lag Time).
- For Old Crescent: Best Time = Sunrise - 4/9 (Moon Lag Time).

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Conclusion

This  software meets all of my requirements (Ref 3) for finding favourable TLCs without further ado, especially as it includes early morning events as described above. As my westerly horizon is full of Tuggeranong Hill, so to see evening TLCs requires a short trip in the car to achieve a clear westerly horizon.

References

1.    Astronomical Society of  New South Wales, Proceedings of the 7th NACAA, session 7A  "Thin Lunar Crescents", Byron W Soulsby CAS.

2.   "Accurate Times" from  http://www.icoproject.org/accut.html

3.    TLC Ages for 2007 at Theodore

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Produced by the Theodore Lunar Observatory, Australia - 2007 February 19

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