# NRIAG Egypt Studies: 1984-2014

## Summary

The National Research Institute of Astronomy and Geophysics (NRIAG, Egypt) conducted the
most extensive body of peer-reviewed naked-eye Fajr observations anywhere in the world.
Multiple campaigns from 1984 to 2014 covered six Egyptian sites across a wide range of
latitudes, elevations, and atmospheric conditions.

## Key Paper

Hassan, A.H., et al. "Astronomical determination of the proper time for Fajr prayer."
*NRIAG Journal of Astronomy and Geophysics*, 3(1): 23-26, 2014.
DOI: S2090997714000054

## Sites and Findings

| Site | Lat/Lng | Elevation | Years | Mean Fajr Angle | Conditions |
| --- | --- | --- | --- | --- | --- |
| Kottamia Observatory | 30.03°N, 31.83°E | 477m | 1984-1987 | 13.5° | Elevated desert observatory; photoelectric + naked eye |
| Helwan | 29.86°N, 31.34°E | 114m | 1984-1987 | 13.1° | Peri-urban; slight light pollution |
| Aswan | 24.09°N, 32.90°E | 92m | 1984-1987 | 14.0° | Near-equatorial desert; clearest conditions |
| Siwa Oasis | 29.20°N, 25.52°E | -18m | 2005-2007 | 14.8° | Below sea level; very dry; exceptional clarity |
| Mersa Matrouh | 31.36°N, 27.24°E | 26m | 2005-2007 | 13.7° | Mediterranean coast |
| Assiut | 27.17°N, 31.17°E | 55m | 2010-2013 | 13.7° | Nile Valley; agricultural; slightly lower than desert |

## Second NRIAG Paper

Hassan, A.H., et al. "Determination of Fajr twilight at five Egyptian sites."
*NRIAG Journal of Astronomy and Geophysics*, 5: 9-15, 2016.

Sites: Sinai (31.07°N, 30m), Assiut (27.17°N, 55m), Kharga Oasis (25.45°N, 74m), Qena
(26.16°N, 96m), and others. Results consistent with earlier campaign: 13°-15°.

Sinai desert specifically: 14.84° mean angle (n=47 nights).
Nile Valley sites: systematically lower by ~1° (agricultural aerosols reducing sky clarity).

## Isha Findings

The same papers cover Isha (Shafaq al-Abyad, white dusk twilight):
- Mean Isha angles: 14.3°-15.8° across Egyptian sites
- Shafaq al-Ahmar (red dusk) disappears earlier: ~10°-12°

## Key Conclusions

1. The 18° convention overstates true dawn by a significant margin. At most Egyptian sites, the
   sky begins to lighten at 13°-15° depression.
2. Desert sites consistently yield slightly higher angles than agricultural or coastal sites,
   likely due to atmospheric aerosol differences.
3. Results are consistent across a 30-year span (1984-2014) and multiple independent teams.
4. No systematic seasonal trend is reported — but Egypt spans only 22°-31°N, limiting latitude
   range for seasonal analysis.

## Data Note

These papers report mean angles and statistical distributions, not per-date timestamps with
explicit times. The per-date ML training records for Egypt in this project are derived from
the published means using estimated observation times, and are marked accordingly in
`data/raw/sources.md`.
