Why iftar time varies by 1-3 minutes from astronomical sunset time

بِسۡمِ ٱللَّهِ ٱلرَّحۡمَٰنِ ٱلرَّحِيمِ 

Prayer timetables can differ by 1–2 minutes from the actual visible sunset for several technical reasons.

Actual sunset can be 3 minutes after theoretical sunset reported in news papers and most Apps in cell phones. This is based on 3 things:

1. Actual pressure, temperature, and humidity conditions at sunset in your exact location. This causes a refraction effect that makes disc of the sun still visible above the horizon.

2. Areas around the actual latitude and longitude

3. Any downward sloping ground towards sunset direction. 

The main ones are related to astronomical calculations and local observation conditions.

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1️⃣ Atmospheric Refraction

When sunlight passes through the Earth’s atmosphere, it bends slightly (a phenomenon called refraction).

Because of this:

• The sun appears slightly higher than it actually is.

• You can still see the sun even though it is already geometrically below the horizon.

Astronomical sunset calculations therefore include a correction of about 34 arc-minutes for atmospheric refraction and 16 arc-minutes for the sun’s radius.

This standard model is used by organizations like the National Oceanic and Atmospheric Administration and the United States Naval Observatory.

Small variations in atmospheric pressure or temperature can shift the observed sunset by about 1 minute.

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2️⃣ Elevation Above Sea Level

If you are standing higher than sea level (e.g., in a tall building or hill):

• You can see farther beyond the horizon.

• The sun will appear to set slightly later.

Even 50–100 meters elevation can change sunset by ~30–60 seconds.

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3️⃣ Geographic Coordinates Used

Prayer timetables usually calculate times for the center of a city.

But if you are:

• Several kilometers east or west of that point

• In a large city the actual sunset at your exact location may differ by 30–90 seconds.

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4️⃣ Rounding in Prayer Timetables

Many prayer schedules round times to:

• the nearest minute, or

• 1 minute earlier/later as a safety margin.

For example:

• Calculated sunset: 6:19:42 PM

• Timetable may show: 6:19 PM or 6:20 PM

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5️⃣ Safety Margin for Maghrib

Some masjids intentionally add 1–2 minutes delay before announcing Maghrib to ensure:

• the sun has fully disappeared

• there is no risk of breaking the fast early

This is based on the instruction of the Prophet ﷺ in authentic reports in Sahih al-Bukhari and Sahih Muslim that fasting ends when the sun has set.

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✅ Summary

Reason	Possible Difference
Atmospheric refraction variation	~1 minute
Elevation	~30–60 seconds
City coordinate differences	~30–90 seconds
Rounding in timetables	up to 1 minute
Safety margin by masjid	1–2 minutes

So a 1–2 minute difference is normal and expected between calculated prayer timetables and what you observe with the naked eye.