Fajr Time,
Determined by Light Itself
Physics-based prayer time calculation using Monte Carlo radiative transfer through Earth's real atmosphere
وَكُلُوا وَاشْرَبُوا حَتَّىٰ يَتَبَيَّنَ لَكُمُ الْخَيْطُ الْأَبْيَضُ مِنَ الْخَيْطِ الْأَسْوَدِ مِنَ الْفَجْرِ
“…and eat and drink until the white thread of dawn becomes distinct to you from the black thread of night…”
Surah Al-Baqarah 2:187Traditional Methods Fall Short
The Quran defines Fajr as when dawn light becomes visible. A physics question, not a geometry one
Traditional Method
- × Fixed 18° angle for everyone on Earth
- × Same time regardless of weather conditions
- × Ignores clouds, pollution, and atmosphere
- × Mathematical abstraction, not what you see
Physics Method
- ✓ Simulates actual photon propagation
- ✓ Real-time weather and atmosphere data
- ✓ Models clouds, aerosols, and terrain
- ✓ Calculates what your eyes would observe
On a heavily overcast day, thick clouds block scattered twilight light, making the "white thread" visible later. A physics-based simulation accounts for this by calculating what you would actually observe.
From Atmosphere to Prayer Time
Four steps to compute physically accurate Fajr time for your location
Fetch Atmosphere
Real-time clouds, aerosols, and temperature from NASA, ECMWF, and NOAA satellites
Build the Sky
49 sun angles, 41 wavelengths, layered atmosphere model up to 23km altitude
Simulate Light
40 billion+ photons reverse-traced from observer to sun through scattering, absorption, and reflection paths
Find Fajr
Determine the exact moment when dawn light crosses the human visibility threshold
Photon scattering simulation through atmospheric layers
Physics-Accurate Fajr Time
A sample calculation showing how weather conditions affect the result
Flensburg, Germany · December 31, 2025
Rayleigh & Mie Scattering
Light interacts with air molecules and cloud droplets at every atmospheric layer
Human Vision Model
Weighted by mesopic (twilight) eye sensitivity centered at 530nm
GPU Accelerated
40 billion+ photon paths reverse-traced in minutes using SMART-G engine
Terrain & Surface
Elevation, snow cover, and ground albedo affect reflected twilight light
Why Accuracy Matters
If Fajr is Too Early
You stop eating before necessary. Inconvenient and makes the fast harder, but the fast remains valid.
If Fajr is Too Late
You might eat after true dawn has begun. This could potentially invalidate the fast, a serious concern during Ramadan.
During Ramadan, the Fajr time determines when fasting begins. Even a few minutes of error can mean eating after true dawn or unnecessarily starting too early.
The Quran defines Fajr by what you can see: the white thread becoming distinct from the black thread. This is a question about light propagating through the atmosphere to reach human eyes.