Is 15 Degrees More Accurate Than 18 for Calculating Fajr and Isha?
Question
I have read an article arguing that fixed degree calculations for Fajr and Isha are unreliable and that 15 degrees is a better approximation than 18 degrees. The article claims twilight varies by season, latitude, altitude, and other factors, and therefore recommends 15° as a middle approximation between 12° and 18°. It suggests that 18° is not necessarily accurate and that 15° is a more practical solution. Is this correct? Should 15° be preferred over 18°?
Answer
Alhamdulillah, wassalatu wassalamu ala rasulillah, wa ala alihi wa sahbihi ajmain.
1. The Shari Context
Allah defines the beginning of Fajr by a visible sign:
“Eat and drink until the white thread of dawn becomes distinct to you from the black thread of night.”
Surat al Baqarah 2:187
The Prophet ﷺ clarified that true dawn (fajr sadiq) is the horizontal spreading light across the horizon, distinct from the false vertical dawn.
Sharia did not define Fajr by astronomical degrees. Degrees are modern tools used to approximate the visible sign when direct observation is difficult due to urbanization and light pollution.
The obligation is tied to the appearance of true dawn, not to any specific numerical calculation.
2. Scholarly Discussion
Classical scholars did not speak in degrees, but later Muslim astronomers correlated true dawn with approximately 18 degrees of solar depression, sometimes 17 to 19 depending on region. Over time, 18° became the dominant global reference in Muslim lands.
Major institutions worldwide adopted approximately 18°:
Muslim World League
University of Islamic Sciences, Karachi
Many European and Asian councils
The 15° standard emerged much later in North America through specific localized observational studies. It was not historically the dominant standard in Muslim astronomical tradition.
The argument that twilight varies by season, latitude, and altitude is correct. However, variability does not automatically justify lowering the degree. The question is which approximation most consistently aligns with the Sharia defined true dawn.
Choosing 15° merely because it is the midpoint between reported ranges of 12° to 18° is not a juristic or scientific proof. Sharia requires approximation of the sign itself, not an average between observations.
Furthermore, many observational studies suggesting lower degrees were conducted:
In urban environments with heavy light pollution.
With observer variability.
In high latitudes where twilight behaves unusually.
Light pollution can delay visible horizontal light, making dawn appear later than its actual astronomical occurrence.
3. Application to the Issue
The practical difference between 15° and 18° can be 15 to 25 minutes, sometimes more in higher latitudes.
If 15° is used and true dawn occurs earlier, two serious consequences follow:
Fajr prayer may be performed before its time.
Eating may continue after the actual start of fasting, invalidating the fast.
If 18° is used and true dawn occurs slightly later, the consequence is precaution. Stopping slightly early does not invalidate fasting.
This difference is significant.
In acts of worship tied to strict time boundaries, precaution is weightier than convenience.
For this reason, most masajid continue to adopt 18°:
It has broader historical continuity.
It is globally standardized.
It is safer for fasting.
It avoids risking invalid worship.
4. Relevant Usul Principle
الاحتياط في العبادات أولى
Precaution in acts of worship is preferable
When validity depends on precise timing, adopting the earlier and safer estimate protects the integrity of the act.
الحكم يدور مع علته وجودا وعدما
The ruling revolves around its effective cause
The cause for Fajr is the appearance of true dawn. If 18° more consistently captures that cause globally, it is stronger.
اليقين لا يزول بالشك
Certainty is not removed by doubt
A long standing global standard should not be replaced by localized uncertainty without decisive proof.
Final Ruling
While twilight observation varies and degree calculations are approximations, the 18° standard remains historically grounded, globally adopted, and juristically safer. The 15° method is a minority ijtihadi position and does not outweigh the precautionary and majority based strength of 18°. For the protection of prayer and fasting validity, 18° remains the stronger and more accurate standard.
And Allah knows best.