pray-calc-ml/.github/wiki/Research-Notes.md

# Research Notes

Summaries of the academic papers and observation programs that contributed records to this dataset.

For full citation details, see [Data Sources](Data-Sources).

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## Key Finding

The data consistently shows three main patterns:

1. **Equatorial sites produce higher depression angles than mid-latitude sites.** Near the equator,
   the sun rises at a steep angle through the horizon, compressing the twilight interval. At 3°-7°
   latitude, mean Fajr angles are 16°-17°. At 52°N (Birmingham), the mean is ~13°.

2. **Season matters at every latitude.** Fajr angles are consistently higher in winter and lower
   in summer at northern hemisphere sites. Birmingham's 10-year dataset shows a ~3° peak-to-trough
   sinusoidal seasonal pattern.

3. **Elevation shifts the angle upward.** Sites above 500m (Kottamia 477m, Hail 1020m, Tehran 1191m,
   Amman 1000m, Ankara 890m, Tehran 1191m) consistently produce angles at the high end of their
   latitude band. The effect is smaller than latitude or season but real.

---

## Papers by Region

### Egypt — NRIAG Series

The National Research Institute of Astronomy and Geophysics (NRIAG) in Egypt has published the
longest series of peer-reviewed Fajr and Isha observation studies.

**Hassan et al. 2014** — *NRIAG Journal of Astronomy and Geophysics*, 3: 23-26.

Photoelectric and naked-eye observations at two contrasting Egyptian sites:
- Kottamia Observatory (477m, desert): mean Fajr 14.0°, Isha (Shafaq Abyad) 13.8°
- Aswan (92m, very clear desert near Tropic): mean Fajr 13.2°

The Kottamia results are the most reliable pre-SQM era Egyptian data. Photoelectric twilight
sensors provide an objective measure of sky brightness at the moment of civil twilight.

**Hassan et al. 2016** — *NRIAG Journal of Astronomy and Geophysics*, 5: 9-15.

Extended the Egyptian dataset to two additional sites:
- North Sinai (30m, open desert): mean Fajr 13.5° across four seasons
- Assiut (55m, Nile valley): mean Fajr 13.2° (slightly lower, attributed to agricultural aerosols)

The consistent result across Egyptian desert sites (13°-14.5°) is notable given that the MUIS/ISNA
and most calculators use 18° or 15°.

**Semeida & Hassan 2018** — *Beni-Suef University Journal of Basic and Applied Sciences*, 7: 286-290.

38 observation nights at Wadi Al Natron (pure desert, no light pollution):
- Fajr: 13.5°-14.8° across seasons
- Isha (Shafaq Abyad): 13.0°-15.2° across seasons

This paper provides the most complete Egyptian Isha dataset.

**Rashed et al. 2022** — *International Journal of Mechanical Engineering and Technology*, 13(10).

SQM + naked eye at Fayum (29.28°N, near the Fayum depression):
- Seasonal means: winter 14.5°, summer 13.1°

**Rashed et al. 2025** — *NRIAG Journal of Astronomy and Geophysics*.

Most recent NRIAG journal paper. Alexandria (Mediterranean coast, 31.2°N):
- Three seasons: winter 14.1°, summer 12.9°, autumn 13.8°

**Rashed & Hassan 2025** — *In: Islamic Calendar and Prayer Times*, Springer, ISBN 978-981-96-3276-3, chapter 14.

The most comprehensive modern Egypt study. CCD photometry + SQM-L + naked eye across six sites
in Egypt, 1300+ observation nights from August 2015 to December 2019. Mean D0 values reported
per site per season.

| Site | Lat | Elev | D0 mean | Notes |
| --- | --- | --- | --- | --- |
| Kottamia Observatory | 29.929°N | 477m | 14.66° ±0.20° | Primary site, highest data density |
| Alexandria (coast) | 31.2°N | 32m | 13.4° | Mediterranean boundary layer effects |
| Matrouh | 31.35°N | 27m | 13.8° | Northwestern desert, low humidity |
| Marsa Alam | 25.07°N | 20m | 13.5° | Southern Red Sea coast |
| Sohag | 26.56°N | 62m | 13.9° | Upper Nile agricultural valley |
| Dahab (Sinai) | 28.5°N | 5m | 14.2° | Mountain-backed coastal site |

Consistent result across all Egyptian sites (13.4°-14.7°) from modern instrumental methods.
The inter-site variation is real: lower angles at Alexandria are consistent with boundary-layer
aerosols scattering light and elevating sky brightness before true dawn.

Entered in dataset as seasonal proxy records (4 seasons per site = 24 Fajr records).

---

### Saudi Arabia — Khalifa 2018

**Khalifa 2018** — *NRIAG Journal of Astronomy and Geophysics*, 7: 22-28.

80 observation nights at Hail (27.52°N, 1020m elevation, Najd plateau), with 32 nights selected
for excellent atmospheric transparency (no clouds, no dust).

Results:
- Mean Fajr: 14.4° (range 12.8°-16.1°)
- Mean Isha (Shafaq Abyad): 14.8° (range 13.2°-16.4°)
- Higher in winter, lower in summer

At 1020m, Hail shows a clearly elevated angle vs sea-level desert sites in Egypt. This is
the primary evidence for the elevation effect.

---

### Malaysia and Indonesia — Equatorial Studies

**Kassim Bahali et al. 2018** — *Sains Malaysia*, 47(11): 2797-2805.

The strongest low-latitude Fajr study. 64 observation days using DSLR astrophotography combined
with Sky Quality Meter measurements across Malaysia and nearby Indonesia (2°N to 7°S).

Key results:
- Mean Fajr depression: **16.67°** (range 13.9°-19.8°)
- Standard deviation: 1.32°
- No correlation with season at these low latitudes

The DSLR + SQM combination is methodologically more rigorous than naked eye alone. The SQM
provides an objective sky brightness threshold independent of observer judgment.

**Saksono 2020** — *NRIAG Journal of Astronomy and Geophysics*, 9(1): 238-244.

SQM-only study at Depok, West Java (6.4°S, 65m), 26 nights in June-July 2015:
- Mean Fajr depression: ~16°
- High consistency with Kassim Bahali despite different instruments

**Hamidi 2008** — Academia.edu working paper.

Shafaq al-Abyad (Isha) observations at two Malaysian sites:
- Kuala Lipis (4.183°N): ~17° across seasons
- Port Klang (3.004°N): ~16°-17° across seasons

The ~17° Isha result at low latitudes mirrors the ~17° Fajr result — both twilight phenomena
are compressed by the steep solar arc at equatorial sites.

**OIF UMSU 2017-2020** — University of Muhammadiyah North Sumatra.

Hundreds of SQM observation nights at Medan (3.595°N):
- Proposed national Indonesian standard: 16.48° for Fajr
- Isha: consistent with ~17°

---

### United Kingdom

**Hizbul Ulama UK 1987-1989**

21 successful Fajr observations over three years from a rural Lancashire site (53.748°N, 120m).
One of the earliest systematic UK observation programs. Per-season seasonal results published
at http://www.hizbululama.org.uk/files/salat_timing.html.

Fajr results: consistent 12°-14° range across seasons. Isha observations also recorded.

**Asim Yusuf 2017** — *Shedding Light on the Dawn*, ISBN 978-0-9934979-1-9.

The highest-quality UK observation study. Multi-observer consensus across three to eight
observers on each selected night. Site: Exmoor National Park (51.15°N, 430m), one of the
darkest skies in southern England (International Dark Sky Reserve).

Per-season results from 2013-2016:
- Winter: Fajr ~13.8°, Isha (Shafaq Abyad) ~14.2°
- Summer: Fajr ~12.1°, Isha ~12.8°

The multi-observer consensus methodology makes these the most reliable UK data points.

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### Moonsighting.com / Khalid Shaukat

A multi-decade global observation network. Shaukat coordinated observers across Chicago,
Buffalo, Toronto, Karachi, Cape Town, Auckland, and Trinidad from the 1990s through the 2010s.

Documented times represent per-date naked-eye observations with explicit sunrise verification.
The "90-111 minutes before sunrise" figure for Chicago is consistent with a 13°-14° depression
at 41.9°N across seasons.

---

## Latitude-Angle Summary Table

This table synthesises mean Fajr angles from peer-reviewed sources across the latitude range.
It is the primary input for understanding the latitude effect in the ML model.

| Latitude | Site | Elev | Mean Fajr (°) | N | Method |
| --- | --- | --- | --- | --- | --- |
| 52.5°N | Birmingham, UK | 141m | ~13.0° | 4,018 | Community astrophotography |
| 43.7°N | Toronto, Canada | 76m | ~13.2° | 4 | Naked eye |
| 41.9°N | Chicago, USA | 182m | ~13.1° | 8 | Naked eye |
| 39.9°N | Ankara, Turkey | 890m | ~14.8° | 4 | Naked eye (high elev) |
| 36.9°S | Auckland, NZ | 20m | ~14.8° | 2 | Naked eye |
| 37.8°S | Melbourne, AU | 31m | ~14.5° | 3 | Naked eye |
| 35.7°N | Tehran, Iran | 1191m | ~15.1° | 3 | Naked eye (very high elev) |
| 34.0°N | Fez, Morocco | 408m | ~14.2° | 4 | Naked eye |
| 33.9°S | Cape Town, SA | 10m | ~15.2° | 4 | Naked eye |
| 31.9°N | Amman, Jordan | 1000m | ~14.9° | 3 | Naked eye (high elev) |
| 31.0°N | Alexandria, Egypt | 32m | ~13.6° | 3 | SQM |
| 30.5°N | Wadi Al Natron | 23m | ~14.0° | 7 | Naked eye (desert) |
| 30.0°N | Kottamia, Egypt | 477m | ~14.0° | 6 | Photoelectric (high elev) |
| 27.5°N | Hail, Saudi Arabia | 1020m | ~14.4° | 8 | Naked eye (high elev) |
| 24.9°N | Karachi, Pakistan | 8m | ~14.8° | 4 | Naked eye |
| 14.7°N | Dakar, Senegal | 24m | ~15.3° | 2 | Naked eye |
| 12.0°N | Kano, Nigeria | 476m | ~15.1° | 2 | Naked eye |
| 10.7°N | Trinidad | 12m | ~15.8° | 2 | Naked eye |
| 6.4°S | Depok, Indonesia | 65m | ~16.0° | 3 | SQM |
| 3.6°N | Medan, Indonesia | 22m | ~16.5° | 8 | SQM |
| 3.1°N | KL, Malaysia | 40m | ~16.7° | 4 | DSLR + SQM |
| 4.1°S | Mombasa, Kenya | 50m | ~16.2° | 2 | Naked eye |

The counter-intuitive result — equatorial sites have *higher* angles than mid-latitude sites —
is a consequence of the Sun's steep rise angle at low latitudes. The same depression angle
corresponds to a longer time before sunrise at higher latitudes, so "true dawn" at those
latitudes occurs at a shallower angle.

---

## Open Questions

1. **Why do southern hemisphere sites at 33°-37°S (Cape Town, Auckland, Melbourne) show higher
   angles (~15°) than northern hemisphere sites at the same latitudes (UK at 51°N, 13°)?**
   One hypothesis: the northern hemisphere has more industrial aerosols, which reduce sky
   transparency and shift the observer's perception of "true dawn" to a later, shallower angle.
   This would bias northern hemisphere data toward lower angles. The effect needs more data to confirm.

2. **Is the elevation effect physically explained or confounded?**
   The high-elevation sites (Tehran 1191m, Amman 1000m, Hail 1020m, Ankara 890m) all show
   elevated angles vs sea-level sites at similar latitudes. The physical explanation (observer above
   more of the atmosphere) is plausible but the magnitude needs testing with more elevation data
   points that control for geography, season, and atmospheric conditions.

3. **Why does Isha (Shafaq Abyad) at ~15° match Fajr at ~13°-16° for most sites?**
   The Shafaq al-Abyad criterion requires the white twilight to disappear, which is a different
   type of observation from true dawn (false dawn appearance). It is not a priori obvious they
   would produce similar depression angles. The similarity may be coincidental, or it may reflect
   a shared physical threshold in sky brightness.

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