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6e0f4a679c
Replaces the original JS calibration library with a pure Python pipeline for collecting and back-calculating solar depression angles from human-verified Fajr and Isha prayer sightings. What this does: - src/pipeline.py: master pipeline; fetches iCal + manual records, back-calculates angles via PyEphem, applies quality filters, exports two clean CSVs - src/collect/openfajr.py: parses the OpenFajr Birmingham iCal feed (~4,018 records) - src/collect/verified_sightings.py: manually compiled records from peer-reviewed studies (Egypt, Saudi Arabia, Malaysia, Indonesia, UK, USA, Canada, and more) - src/angle_calc.py: PyEphem back-calculation with atmospheric refraction - src/elevation.py: Open-Elevation API batch lookup Datasets generated: - data/processed/fajr_angles.csv: 4,105 confirmed Fajr records, 35 locations, latitude range -37.8 to 53.7 degrees, date range 1985-2026 - data/processed/isha_angles.csv: 43 confirmed Isha records, 20+ locations Also includes: - notebooks/01_exploratory_analysis.ipynb: latitude, TOY, elevation pattern analysis - research/: academic paper summaries (not training data) - data/raw/sources.md: full citation table for all data sources
56 lines
2.6 KiB
Markdown
56 lines
2.6 KiB
Markdown
# OpenFajr Project (Birmingham, UK)
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## Overview
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OpenFajr is an ongoing community astrophotography project in Birmingham, UK, where a panel
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of scholars and community members review daily sky photographs and vote on the moment of
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true dawn. This is the largest dataset of per-date human-verified Fajr sightings in the world,
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with over 4,000 records spanning 2016 to the present.
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**URL:** https://openfajr.org
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**Data format:** Google Calendar iCal feed (UTC)
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**Location:** Birmingham (52.4862°N, 1.8904°W, 141m)
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## Method
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Each morning, a wide-field camera captures a continuous series of sky photographs from the
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eastern horizon. After each session, an independent panel reviews and votes on the photographs
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to identify the moment when the horizon first becomes distinguishable (true dawn / Subh Sadiq).
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The voted time is published to the iCal feed.
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## Findings
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Birmingham is at 52°N, which produces interesting seasonal variation. The dataset covers over
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10 years and shows:
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- **Mean depression angle:** approximately 12.5°-13.5° (computed in this project via back-calculation)
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- **Seasonal variation:** lower angles in summer (shorter, shallower twilight arc), higher in winter
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- **Winter range:** typically 13.5°-15.0°
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- **Summer range:** typically 11.5°-13.5° (sun moves at a shallower angle through the horizon zone)
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- **Inter-year consistency:** very stable year-to-year
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## Why Birmingham
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Birmingham's latitude (52°N) is notable because it experiences significant seasonal variation in
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both the angle and duration of twilight. At this latitude in summer, nights are very short and
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twilight begins to overlap with morning civil dawn — the solar arc through the horizon zone is
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much shallower, meaning false dawn and true dawn phenomena behave differently than at tropical
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latitudes.
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This makes Birmingham a particularly useful calibration anchor because:
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1. It covers an extreme of the northern temperate zone
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2. 10+ years of consistent data provides excellent statistical confidence
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3. The scholarly review process provides strong validity guarantees
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## DST Artifacts
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The iCal feed contains a small number of records around British Summer Time transition dates
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(last Sunday of March, last Sunday of October) with anomalous UTC timestamps. These appear to
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result from timezone confusion in calendar software and produce depression angles of 3°-7°,
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which are physically impossible for genuine Fajr sightings. The pipeline filters these out.
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## Use in This Project
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OpenFajr provides ~98% of the Fajr training data. The raw iCal is fetched at runtime by
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`src/collect/openfajr.py`. No local caching is performed; run the pipeline with network access
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to get the latest feed.
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