What does a Fajr angle describe?
The angle is the sun's depression below the horizon. Before sunrise, the sun reaches 18° below the horizon before it reaches 15°. The angle is not a number of minutes before sunrise, and three degrees cannot be converted into one universal time offset.
Astronomical twilight uses an 18° boundary in astronomical terminology. That definition alone does not establish which religious convention a community should follow. Dawn visibility and the adoption of a prayer timetable are separate questions from calculating when a geometric angle is reached.
15° and 18° Fajr across four cities
For these 16 samples, the 18° calculation is 12–27 minutes earlier. This is the range in this table, not a worldwide minimum or maximum.
| City / time zone | Date | Fajr 15° (ISNA) | Fajr 18° (Karachi) | 18° earlier by |
|---|---|---|---|---|
| Karachi Asia/Karachi | 21 March 2027 | 5:33 AM | 5:20 AM | 13 min |
| Karachi Asia/Karachi | 21 June 2027 | 4:30 AM | 4:14 AM | 16 min |
| Karachi Asia/Karachi | 21 September 2027 | 5:17 AM | 5:04 AM | 13 min |
| Karachi Asia/Karachi | 21 December 2027 | 6:04 AM | 5:50 AM | 14 min |
| New York America/New_York | 21 March 2027 | 5:43 AM | 5:26 AM | 17 min |
| New York America/New_York | 21 June 2027 | 3:45 AM | 3:18 AM | 27 min |
| New York America/New_York | 21 September 2027 | 5:27 AM | 5:10 AM | 17 min |
| New York America/New_York | 21 December 2027 | 5:54 AM | 5:38 AM | 16 min |
| Singapore Asia/Singapore | 21 March 2027 | 6:12 AM | 6:00 AM | 12 min |
| Singapore Asia/Singapore | 21 June 2027 | 5:58 AM | 5:45 AM | 13 min |
| Singapore Asia/Singapore | 21 September 2027 | 5:58 AM | 5:46 AM | 12 min |
| Singapore Asia/Singapore | 21 December 2027 | 5:59 AM | 5:46 AM | 13 min |
| Sydney Australia/Sydney | 21 March 2027 | 5:50 AM | 5:35 AM | 15 min |
| Sydney Australia/Sydney | 21 June 2027 | 5:46 AM | 5:30 AM | 16 min |
| Sydney Australia/Sydney | 21 September 2027 | 4:39 AM | 4:24 AM | 15 min |
| Sydney Australia/Sydney | 21 December 2027 | 4:16 AM | 3:56 AM | 20 min |
What was held constant?
Each pair uses the same city-centre coordinates, local date, time zone and library rounding. We run SalahTable's existing ISNA and Karachi presets: their Fajr angles are 15° and 18°, with no added Fajr minutes. The presets also use different Isha angles, but that parameter does not enter the Fajr calculation.
Both runs use the same recommended high-latitude rule. The sample cities are below 45° absolute latitude, and these sample dates do not require that rule to limit the calculated Fajr. The table therefore illustrates the angle difference without mixing it with a high-latitude fallback.
Why latitude and season matter
New York, Karachi and Singapore do not traverse the same dawn angles at the same rate. Sydney adds a southern-hemisphere comparison: June is its winter, while December is its summer. Even when two cities share a date, their minute differences need not match.
The city links above open today's timetable, not the historical or future example row. Use the date shown in the table when reproducing the comparison.
When this comparison stops being sufficient
In northern summer, some locations never reach 18° below the horizon overnight. An app may then apply a night-fraction rule, a seasonal rule or another local convention. A method labelled “18°” does not imply that every displayed summer Fajr is a direct 18° crossing. Our high-latitude guide covers that situation.
Which setting should I use?
Check the convention published by your mosque or local authority. This comparison explains the numerical consequences of two settings; it does not validate one against observed dawn. SalahTable's methodology page lists its country defaults, and each city page offers a method selector.