Islamic prayer times are not arbitrary — they are calculated from the precise position of the Sun relative to the horizon at your location. The five daily prayers each correspond to a distinct astronomical event, which is why the times shift by a few minutes every day and vary considerably between cities. This guide explains the astronomy behind each prayer and the method used on this site.
The astronomical event behind each prayer
Fajr — true dawn
Fajr begins at true dawn (astronomical dawn), when the first light of the Sun appears as a horizontal band stretching across the eastern horizon. This is defined as the moment when the Sun's centre is 18° below the horizon (solar depression angle of 18°). At this point the sky begins to lighten, even though the Sun is still well below the horizon.
Dhuhr — solar noon
Dhuhr begins shortly after solar noon — the exact moment when the Sun reaches its highest point in the sky (the zenith transit). The prayer time is set a few minutes after this transit to ensure the Sun has begun its descent. Dhuhr is therefore the most stable of all prayer times and shows the least seasonal variation.
Asr — afternoon shadow
Asr is calculated from the length of an object's shadow relative to its height. According to the majority of scholars (Shafi'i, Maliki, Hanbali), Asr begins when the shadow of a vertical object equals its own height (plus the length of its shadow at solar noon). The Hanafi school calculates Asr when the shadow is twice the object's height — making Hanafi Asr noticeably later, especially in summer.
Maghrib — sunset
Maghrib is the simplest to calculate: it begins immediately after sunset, defined as the moment the upper limb of the Sun disappears below the western horizon. Maghrib is the most precise of the five prayers — it varies with the calendar just like sunrise and sunset in any almanac.
Isha — nightfall
Isha begins at the disappearance of the red twilight glow from the western sky — defined as the Sun being 17° below the horizon. This is called astronomical dusk or the end of evening twilight. At Isha, the sky is fully dark and the night has properly begun.
The calculation method used on this site
This site uses Method 3 — the Muslim World League (MWL) standard, which is the most widely adopted method in the UK and Europe:
- Fajr: Sun at 18° below the horizon (true astronomical dawn)
- Isha: Sun at 17° below the horizon (true astronomical dusk)
- Asr: Shafi'i/standard school (shadow equals object height)
- Dhuhr: Solar noon + 1–3 minutes
- Maghrib: Immediate after sunset
Why do prayer times change every day?
The Earth orbits the Sun on a tilted axis (23.5°). As the Earth moves through the year, the Sun appears at different heights above the horizon and rises and sets at different times. In summer, the Sun reaches a high altitude and stays up longer; in winter, the opposite. This is why Fajr in London can be as early as 02:40 in late June and as late as 06:20 in December. Dhuhr barely changes, while Fajr and Isha show the most variation.
What about high-latitude challenges?
At high latitudes like Scotland, the Sun in summer never descends far enough below the horizon for true astronomical twilight to end. This means the MWL criterion for Isha (Sun at 17°) is never met on long summer nights. Scholars have agreed on approximation methods for these situations — the most common being to use the time from a reference latitude (45°N) or to use a fixed proportion of the night. UK mosques handle this through their local ijazah (scholarly permission).
Frequently asked questions
Why are prayer times different in different cities?
Because prayer times depend on the Sun's position at your specific location. London and Edinburgh are at different latitudes (51.5°N vs 55.9°N) and different longitudes, so the Sun rises, sets, and reaches its zenith at different times. Even cities at the same latitude but different longitudes will have slightly different prayer times.
Are the times the same as iqamah times?
No. The adhan (call to prayer) time marks when the prayer becomes due. Iqamah (congregation start) is typically 10–20 minutes later, allowing time for wudu and gathering. Mosque iqamah times vary and should be confirmed directly with your local mosque.
Which calculation method do UK mosques use?
The majority of UK mosques use Method 3 (Muslim World League) or ISNA. The Wifaqul Ulama UK timetable (widely used by deobandi mosques) uses fixed local times based on confirmed sunrise/sunset calculations. Most published UK prayer timetables are based on MWL angles (Fajr 18°, Isha 17°) as used on this site.