Why prayer times move every day
the solar geometry behind the timetable

Open a prayer timetable on two neighboring days and every entry may move by a minute or more. Change the city and the differences can become much larger. Travel far north or south, and the spacing between Fajr, sunrise, Maghrib, and Isha may look completely different. This is expected because the timetable follows the apparent motion of the Sun, not a universal set of clock hours.

Earth rotates once per day, but it also moves around the Sun with a tilted axis. The Sun's declination therefore changes through the year, shifting the length of daylight and the path the Sun appears to take across the local sky. Latitude determines how steeply that path crosses the horizon. Longitude determines when local solar events occur relative to a time-zone clock.

The five prayer times do not all use the same astronomical trigger. Fajr and Isha are tied to twilight conventions. Dhuhr follows solar transit. Asr follows a shadow-length rule. Maghrib follows sunset. This is why one simple offset cannot generate an accurate full timetable.

Before sunrise, the Sun is still below the horizon, yet sunlight scattered by the atmosphere gradually brightens the sky. This interval is twilight. A calculation represents the beginning of Fajr by finding when the geometric center of the Sun reaches a selected depression angle below the horizon. For example, a method using 18 degrees searches for the morning instant at which solar altitude reaches -18 degrees.

There is no single angle used by every published timetable. The Muslim World League commonly uses 18 degrees for Fajr, while the Kemenag option in Jewawud uses 20 degrees. Other regional methods use their own parameters. A larger depression angle is reached earlier before sunrise, so changing the method can noticeably change Fajr even when the location and date remain identical.

The angle is a calculation convention, not a claim that the visible sky behaves identically everywhere. Atmospheric clarity, terrain, haze, light pollution, and the observer's horizon affect what is visually perceived. For practical worship, users should select the method used by their trusted local authority rather than choosing an angle only because its result looks convenient.

Sunrise and sunset sound simpler, but a precise calculator still needs a convention. The atmosphere bends light near the horizon, making the Sun appear slightly higher than its geometric position. The Sun also has a visible disk rather than being a mathematical point. A widely used standard models sunrise and sunset when the Sun's center is about 0.833 degrees below an ideal horizon.

In that model, sunrise is the morning crossing and sunset is the evening crossing. Maghrib begins at sunset in the timetable. The actual view from a balcony or valley can differ because buildings, mountains, elevation, and local refraction change the visible horizon. A mathematical result therefore represents a standardized astronomical horizon, not a guarantee that every observer sees the first or last sliver at exactly that second.

Fasting duration in the Jewawud Prayer & Fasting app is calculated from Fajr to Maghrib. Both ends can move from day to day, so seasonal fasting duration changes even if a person stays in the same city.

Solar noon, also called solar transit, is the moment the Sun crosses the local meridian and reaches its greatest altitude for that day. Dhuhr begins after this transit. Civil noon is simply 12:00 on the time-zone clock, so the two need not coincide.

Two effects create the difference. First, a time zone covers a range of longitudes, while local solar noon shifts by roughly four minutes for each degree of longitude away from the zone's reference meridian. Second, the equation of time describes a seasonal difference between apparent solar time and uniform clock time caused by Earth's orbital eccentricity and axial tilt.

That is why Dhuhr can occur before or after 12:00 and drift through the year. Daylight-saving rules, where used, shift the displayed clock time again without changing the physical position of the Sun. A robust calculator finds solar transit first, applies a small safety offset if configured, and only then converts the result into local civil time.

Asr differs from the other entries because its trigger is expressed through shadow length. Even at solar noon, a vertical object usually has a nonzero shadow unless the Sun is directly overhead. Call that minimum daily shadow s₀ and the object's height h.

Under the standard convention, Asr begins when the total shadow reaches s₀ + h. Under the Hanafi convention, it begins when the total shadow reaches s₀ + 2h. The calculator uses solar altitude and geometry to find the afternoon instant that satisfies the selected rule. The second condition occurs later because the Sun must descend farther before the shadow becomes longer.

This definition explains why Asr cannot be represented by one fixed number of minutes after Dhuhr. The Sun's noon altitude and afternoon descent change with latitude and season, altering how quickly the required shadow length is reached.

After sunset, the Sun continues downward below the western horizon and twilight fades. Many calculation methods define Isha with another solar depression angle. A method may use 17 degrees, 18 degrees, or another regional value. Umm al-Qura instead commonly specifies an interval after Maghrib, with a different Ramadan interval in some implementations.

Because Fajr and Isha depend on conventions, two reputable timetables can agree closely on sunrise, Dhuhr, and Maghrib yet differ more at the edges of the night. That difference does not automatically indicate a programming error. The first question should be: are both timetables using the same method, Asr convention, high-latitude rule, coordinates, and minute adjustments?

Near the equator, daylight duration changes relatively little through the year. At mid-latitudes, summer days become longer and winter days shorter. Farther toward the poles, the seasonal contrast becomes extreme. These changes alter not only sunrise and sunset but also the available darkness in which the Sun can cross a selected Fajr or Isha angle.

Latitude also changes the angle at which the Sun's path crosses the horizon. A shallow crossing can stretch twilight over a long interval. A steep crossing produces a faster transition between darkness and daylight. Longitude shifts the whole pattern relative to civil time, while date and latitude reshape the pattern itself.

At high latitudes during summer, the Sun may set but never descend to the selected Fajr or Isha angle before rising again. The mathematical equation then has no real crossing for that night. Returning a fabricated angle time would be worse than acknowledging that the requested event does not occur under the chosen definition.

Prayer-time systems therefore offer high-latitude conventions. Common choices use the middle of the night, one-seventh of the night, or an angle-based fraction of the night. These are practical rules for exceptional geometry, not additional astronomical observations. Selecting a different rule can substantially change the reported Fajr or Isha.

Jewawud exposes these options instead of silently hiding the problem. Its automatic setting falls back to a night-based rule when the selected twilight crossing cannot be solved. Users in affected regions should follow the convention recommended by a trusted local authority.

The calculation begins with latitude, longitude, calendar date, and time zone. A solar model estimates declination and the equation of time for that date. From those values, the engine finds local solar transit and solves hour-angle crossings for the required apparent solar altitudes.

Sunrise and sunset use the standard apparent-horizon altitude. Fajr and Isha use the selected method's twilight angles or interval. Dhuhr follows transit. Asr uses the selected shadow factor. The engine then applies the chosen high-latitude rule and any explicit minute adjustments before formatting the result in local civil time.

This separation matters. Astronomy determines where the Sun is. A calculation method defines which astronomical condition represents a timetable event. Local settings decide how that event is presented and adjusted. Treating those three layers as one opaque formula makes disagreements difficult to diagnose.

When two sources disagree, compare inputs before comparing outputs. Confirm that both use the same coordinates rather than merely the same city name. Check the time zone and daylight-saving status. Compare the Fajr and Isha method, the Asr convention, the high-latitude rule, elevation assumptions, and any fixed minute offsets.

Then identify where the disagreement occurs. A broad shift affecting every entry often points to longitude, time zone, or daylight-saving configuration. A difference concentrated in Fajr and Isha usually points to twilight angles or high-latitude handling. A difference mainly in Asr usually indicates the shadow convention. A small sunrise or sunset difference can come from horizon, refraction, elevation, or rounding assumptions.

A digital timetable is useful because its assumptions can be inspected and changed. It remains an estimate, however. Use the app as an educational and planning tool, select the method relevant to your region, and defer to local religious guidance when an official timetable is provided.

Think of the daily timetable as six questions asked of the Sun: when does morning twilight reach the selected condition, when does the Sun appear, when does it transit, when does the afternoon shadow reach the selected ratio, when does the Sun disappear, and when does evening twilight reach the selected condition?

Location and date supply the sky geometry. The calculation method supplies the convention. The clock only labels the resulting instants. Once those layers are separated, moving prayer times stop looking arbitrary and become a readable record of Earth's rotation, orbit, axial tilt, and atmosphere.

NOAA Global Monitoring Laboratory: Solar Calculator and its solar calculation equations document solar declination, equation of time, solar noon, sunrise, and sunset calculations.

U.S. Naval Observatory: Rise, Set, and Twilight Definitions distinguishes solar transit, apparent sunrise and sunset, and twilight produced by scattered sunlight.

PrayTimes: Prayer Times Calculation describes common Fajr and Isha angle conventions, the 0.833-degree sunrise and sunset model, Asr shadow factors, and high-latitude adjustments.

Indonesia Ministry of Religious Affairs: Kemenag discussion of the -20-degree Fajr criterion provides context for the Indonesian method available in the app.