Comments on The Iranian Observation
Dr. Monzur Ahmed the author of the program Moon Calculator (V 5.2) sent us his comments on the Iranian observation of Shawwal Crescent on 07 January. Kindly find his comments below.
Assalamu alikum,
Mr. AliReza Mehrani sent in a report of a crescent sighting from Esfahan, Iran on the evening of 7th Jan 2000. I attach the report at the end of this email for reference. He asks for help with calculating the elongation of this sighting. I present here a detailed analysis.
According to Yallop's criterion of crescent visibility, it was theoretically possible to see the crescent from Iran with optical aid only (ie criterion "D: visible with optical aid only" Technical Note No 69, B.D. Yallop, 1998, HMNAO).
Mr. Mehrani gives two sets of latitudes and longitudes. Let us consider the first location from where the sighting was actually made:
Latitude: 32 42' N
Longitude: 52 20' E
Elevation: 1500 m
Time Zone: 3.5 h
The following tables were produced with MoonCalc 5.2:
Topocentric Data at Time of First Sighting (17:25)
_____________________________________________________________________________ _ ESFAHAN A 32:42N 52:20E TZ:+3.5 Ht:1500m JD:2451550.5 Topo Refrac ON _ _ Mag Dec: 3.001 3d 00m 02s approx Date: Fri 7 Jan 2000 _ _ Delta T (TD-UT): 0h 01m 06s approx Time: 17h 25m 00s LT _ _ Apparent Sunrise: 6h 57m 05s LT Apparent Sunset: 17h 16m 19s LT _ _------------------------------------1 of 4-----------------------------------_ _ Moon Alt: 3.869 3d 52m 09s Moon Azi: 242.286 242d 17m 09s _ _ Moon Dec: -20.847 -20d 50m 51s Moon RA: 19.771 19h 46m 16s _ _ Sun Alt: -3.493 -3d 29m 35s Sun Azi: 245.664 245d 39m 49s _ _ Sun Dec: -22.412 -22d 24m 43s Sun RA: 19.197 19h 11m 51s _ _ Rel Alt: 7.362 7d 21m 44s Rel Azi: -3.378 -3d 22m 40s _ _ Elongation: 8.149 8d 08m 56s Moon Age: 19.69h 0D 19H 41M _ _ Phase:0.0062 Mag: -4.86 Width:0.15m Semi-Diam:0.247 Distance:403316.10km _ _-----------------------------------------------------------------------------_ _ Moon Rise: 7h 14m 18s LT Azimuth: 114d 00m 50s _ _ Moon Set: 17h 56m 21s LT Azimuth: 246d 29m 10s _ _ Sunrise-Moonrise: 0h 17m 13s Sunset-Moonset: 0h 40m 02s _ _-----------------------------------------------------------------------------_ _ New Moon: 6 Jan 2000 JDE: 2451550.2602 18h 14m 45s TD _ _ Full Moon: 21 Jan 2000 JDE: 2451564.6955 4h 41m 27s TD _ _ Perigee: 19 Jan 2000 JDE: 2451563.4494 22h 47m 11s TD _ _ Apogee: 1 Feb 2000 JDE: 2451575.5562 1h 20m 52s TD _ _-----------------------------------------------------------------------------_
Topocentric Data at Sunset
_______________________________________________________________________________ _ ESFAHAN A 32:42N 52:20E TZ:+3.5 Ht:1500m JD:2451550.5 Topo Refrac ON _ _ Mag Dec: 3.001 3d 00m 02s approx Date: Fri 7 Jan 2000 _ _ Delta T (TD-UT): 0h 01m 06s approx Time: 17h 25m 00s LT _ _ Apparent Sunrise: 6h 57m 05s LT Apparent Sunset: 17h 16m 19s LT _ _------------------------------------2 of 4-----------------------------------_ _ AT APPARENT SUNSET> _ _ New Moon Visibility (Yallop/-5,q-0.230)D: Visible with optical aid only _ _ Moon Alt: 5.381 5d 22m 50s Moon Azi: 241.067 241d 04m 02s _ _ Sun Alt: -1.381 -1d 22m 51s Sun Azi: 244.529 244d 31m 46s _ _ Rel Alt: 6.761 6d 45m 41s Rel Azi: -3.462 -3d 27m 44s _ _ Elongation: 8.091 8d 05m 27s Moon Age: 19.54h 0D 19H 33M _ _ Phase:0.0061 Mag: -4.86 Width:0.15m Semi-Diam:0.247 Distance:403327.56km _ _-----------------------------------------------------------------------------_
Geocentric Data at Time of First Sighting (17:25)
_______________________________________________________________________________ _ ESFAHAN A 32:42N 52:20E TZ:+3.5 Ht:1500m JD:2451550.5 Geo Refrac OFF _ _ Mag Dec: 3.001 3d 00m 02s approx Date: Fri 7 Jan 2000 _ _ Delta T (TD-UT): 0h 01m 06s approx Time: 17h 25m 00s LT _ _ Apparent Sunrise: 7h 03m 40s LT Apparent Sunset: 17h 09m 44s LT _ _------------------------------------1 of 4-----------------------------------_ _ Moon Alt: 4.584 4d 35m 01s Moon Azi: 242.285 242d 17m 05s _ _ Moon Dec: -20.300 -20d 18m 02s Moon RA: 19.822 19h 49m 21s _ _ Sun Alt: -3.736 -3d 44m 08s Sun Azi: 245.664 245d 39m 49s _ _ Sun Dec: -22.411 -22d 24m 38s Sun RA: 19.198 19h 11m 51s _ _ Rel Alt: 8.319 8d 19m 09s Rel Azi: -3.379 -3d 22m 44s _ _ Elongation: 8.978 8d 58m 40s Moon Age: 19.69h 0D 19H 41M _ _ Phase:0.0062 Mag: -4.86 Width:0.18m Semi-Diam:0.247 Distance:403316.10km _ _-----------------------------------------------------------------------------_
Geocentric Data at Sunset
_______________________________________________________________________________ _ ESFAHAN A 32:42N 52:20E TZ:+3.5 Ht:1500m JD:2451550.5 Geo Refrac OFF _ _ Mag Dec: 3.001 3d 00m 02s approx Date: Fri 7 Jan 2000 _ _ Delta T (TD-UT): 0h 01m 06s approx Time: 17h 25m 00s LT _ _ Apparent Sunrise: 7h 03m 40s LT Apparent Sunset: 17h 09m 44s LT _ _------------------------------------2 of 4-----------------------------------_ _ AT APPARENT SUNSET> _ _ New Moon Visibility (Yallop/-5,q-0.230)D: Visible with optical aid only _ _ Moon Alt: 7.300 7d 18m 00s Moon Azi: 240.124 240d 07m 26s _ _ Sun Alt: -0.833 -0d 50m 00s Sun Azi: 243.655 243d 39m 17s _ _ Rel Alt: 8.133 8d 08m 00s Rel Azi: -3.531 -3d 31m 51s _ _ Elongation: 8.863 8d 51m 47s Moon Age: 19.43h 0D 19H 26M _ _ Phase:0.0060 Mag: -4.85 Width:0.18m Semi-Diam:0.247 Distance:403336.24km _ _-----------------------------------------------------------------------------_
Notes:
- Sunset was at 17:16:19 approx from this location, taking into account the
elevation of 1500m which causes a dip in the horizon and therefore a delay
in sunset.
- If the location was at sea level, then apparent sunset would have been at
about 17:09:44.
- At 17:25 when the crescent was first seen, the *topocentric* elongation
(taking into account parallax and refraction) was 8.149 degrees.
- At 17:25, the *geocentric* elongation or ARCL (ie not taking into account
parallax or refraction) was 8.978 degrees.
- The age of the crescent at first sighting was 19.69 hours.
- At apparent sunset, the topocentric elongation was 8.091 degrees.
- At apparent sunset, the geocentric elongation (ARCL) was 8.863 degrees.
- I attach a gif which shows the predicted crescent
appearance according to MoonCalc 5.2 from Esfahan at 17:25. See the photo below.
Now let us look at the second location, whose co-ordinates and parameters are:
Latitude: 32 40' N
Longitude: 51 40' E
Elevation: 1500 m
Time zone: 3.5 h
Local time: 17:12"
Topocentric Data at 17:12
_______________________________________________________________________________ _ ESFEHAN B 32:40N 51:40E TZ:+3.5 Ht:1500m JD:2451550.5 Topo Refrac ON _ _ Mag Dec: 3.041 3d 02m 28s approx Date: Fri 7 Jan 2000 _ _ Delta T (TD-UT): 0h 01m 06s approx Time: 17h 12m 00s LT _ _ Apparent Sunrise: 6h 59m 40s LT Apparent Sunset: 17h 19m 03s LT _ _------------------------------------1 of 4-----------------------------------_ _ Moon Alt: 6.627 6d 37m 38s Moon Azi: 240.061 240d 03m 38s _ _ Moon Dec: -20.874 -20d 52m 26s Moon RA: 19.765 19h 45m 53s _ _ Sun Alt: -0.174 -0d 10m 25s Sun Azi: 243.602 243d 36m 07s _ _ Sun Dec: -22.413 -22d 24m 47s Sun RA: 19.197 19h 11m 49s _ _ Rel Alt: 6.801 6d 48m 02s Rel Azi: -3.541 -3d 32m 28s _ _ Elongation: 8.065 8d 03m 53s Moon Age: 19.47h 0D 19H 28M _ _ Phase:0.0060 Mag: -4.85 Width:0.15m Semi-Diam:0.247 Distance:403333.25km _ _-----------------------------------------------------------------------------_ _ Moon Rise: 7h 16m 59s LT Azimuth: 114d 00m 13s _ _ Moon Set: 17h 59m 11s LT Azimuth: 246d 29m 51s _ _ Sunrise-Moonrise: 0h 17m 19s Sunset-Moonset: 0h 40m 07s _ _-----------------------------------------------------------------------------_ _ New Moon: 6 Jan 2000 JDE: 2451550.2602 18h 14m 45s TD _ _ Full Moon: 21 Jan 2000 JDE: 2451564.6955 4h 41m 27s TD _ _ Perigee: 19 Jan 2000 JDE: 2451563.4494 22h 47m 11s TD _ _ Apogee: 1 Feb 2000 JDE: 2451575.5562 1h 20m 52s TD _ _-----------------------------------------------------------------------------_
Geocentric Data at 17:12
_______________________________________________________________________________ _ ESFEHAN B 32:40N 51:40E TZ:+3.5 Ht:1500m JD:2451550.5 Geo Refrac OFF _ _ Mag Dec: 3.041 3d 02m 28s approx Date: Fri 7 Jan 2000 _ _ Delta T (TD-UT): 0h 01m 06s approx Time: 17h 12m 00s LT _ _ Apparent Sunrise: 7h 06m 15s LT Apparent Sunset: 17h 12m 28s LT _ _------------------------------------1 of 4-----------------------------------_ _ Moon Alt: 7.403 7d 24m 11s Moon Azi: 240.059 240d 03m 34s _ _ Moon Dec: -20.310 -20d 18m 38s Moon RA: 19.815 19h 48m 53s _ _ Sun Alt: -0.744 -0d 44m 38s Sun Azi: 243.602 243d 36m 07s _ _ Sun Dec: -22.412 -22d 24m 42s Sun RA: 19.197 19h 11m 49s _ _ Rel Alt: 8.147 8d 08m 49s Rel Azi: -3.542 -3d 32m 32s _ _ Elongation: 8.880 8d 52m 49s Moon Age: 19.47h 0D 19H 28M _ _ Phase:0.0060 Mag: -4.85 Width:0.18m Semi-Diam:0.247 Distance:403333.25km _ _-----------------------------------------------------------------------------_Notes:
- The apparent sunset, taking into account the elevation of 1500m is at
17:19:03 approximately.
- The apparent sunset, *not* taking into account the elevation is at 17:12:28.
- Topocentric elongation at 17:12 was 8.065 degrees
- Geocentric elongation (ARCL) at 17:12 was 8.880 degrees
- The age of the crescent at 17:12 was 19.47 hours
- It looks as if EPOCH 2000 was giving geocentric elongation whereas THE SKY was giving topocentric elongation. MoonCalc can give both :-)
Comparison with the sighting by Jim Stamm on 20 Jan 1996 from Tuscon, Arizona
This sighting was reported in Sky and Telescope in the Dec 1996 issue. Prior to publication, there was a heated debate in the Internet newsgroup sci.astro.amateur where some people doubted the validity of this sighting. Anyway, for comparison here is the MoonCalc data:
_______________________________________________________________________________ _ TUCSON 32:10N 110:53W TZ:-7.0 Ht:0m JD:2450102.5 Topo Refrac ON _ _ Mag Dec: 11.810 11d 48m 34s Date: Sat 20 Jan 1996 _ _ Delta T (TD-UT): 0h 01m 02s Time: 17h 57m 06s LT _ _ Apparent Sunrise: 7h 23m 37s LT Apparent Sunset: 17h 45m 39s LT _ _------------------------------------1 of 4-----------------------------------_ _ Moon Alt: 4.494 4d 29m 38s Moon Azi: 250.056 250d 03m 21s _ _ Moon Dec: -14.347 -14d 20m 48s Moon RA: 20.515 20h 30m 53s _ _ Sun Alt: -2.606 -2d 36m 21s Sun Azi: 248.116 248d 06m 58s _ _ Sun Dec: -20.096 -20d 05m 45s Sun RA: 20.163 20h 09m 46s _ _ Rel Alt: 7.100 7d 05m 59s Rel Azi: 1.940 1d 56m 23s _ _ Elongation: 7.646 7d 38m 44s Moon Age: 12.11h 0D 12H 7M _ _ Phase:0.0057 Mag: -4.83 Width:0.15m Semi-Diam:0.278 Distance:358416.75km _ _-----------------------------------------------------------------------------_ _ Moon Rise: 7h 13m 30s LT Azimuth: 108d 09m 55s _ _ Moon Set: 18h 23m 49s LT Azimuth: 253d 37m 21s _ _ Sunrise-Moonrise: -0h 10m 07s Sunset-Moonset: 0h 38m 11s _ _-----------------------------------------------------------------------------_ _ New Moon: 20 Jan 1996 JDE: 2450103.0357 12h 51m 28s TD _ _ Full Moon: 4 Feb 1996 JDE: 2450118.1658 15h 58m 45s TD _ _ Perigee: 19 Jan 1996 JDE: 2450102.4638 23h 07m 52s TD _ _ Apogee: 1 Feb 1996 JDE: 2450115.1561 15h 44m 51s TD _ _-----------------------------------------------------------------------------_
According to Stamms' report, the crescent was seen first at 17:57:06 with a telescope. As you can see, at this time, the topocentric elongation was 7.646 degrees (geocentric elongation 8.630) and the crescent age was 12.11 hours.
THEREFORE IN TERMS OF BOTH MOON AGE AND ELONGATION AT TIME OF FIRST SIGHTING, THE ESFAHAN SIGHTING DOES NOT BEAT THE TUCSON SIGHTING ASSUMING THAT BOTH SIGHTINGS ARE GENUINE POSITIVE SIGHTINGS.
I hope this clarifies things.
Wasalaam.
