How Prayer Times Are Calculated
Every prayer time is a description of where the sun sits relative to the horizon at a specific place and moment. Modern calculation replaces what used to require direct observation of the sky. A formula now predicts the sun's position precisely, for any date and any coordinates, years in advance.
Last updated
One sun, five boundaries
The five boundaries the sun defines
Each of the five daily prayers has a start time defined by a specific solar event or angle.
Fajr
Begins when the sun reaches a set angle below the horizon before sunrise, the point at which true dawn light first appears.
Dhuhr
Begins just after the sun crosses its highest point in the sky for that day, solar noon.
Asr
Begins once an object's shadow reaches a set multiple of its own length beyond its shortest midday shadow.
Maghrib
Begins at sunset, when the sun's disc fully disappears below the horizon.
Isha
Begins when the sun reaches a set angle below the horizon after sunset, when the last twilight glow fades.
Why this needs real astronomy, not a lookup table
The angles for Fajr and Isha are fixed by calculation method. Where the sun actually is at that angle changes every single day and at every point on the earth's surface. Predicting that position accurately requires modelling the earth's orbit, its axial tilt and its rotation together.
The reference implementation most prayer-time software uses is Jean Meeus's published solar-position algorithms, the same family of formulas used in general-purpose astronomy software. This site runs those formulas directly, in code, for each page's own coordinates (see the about page for more on the method).
A Sydney example
Sydney sits at roughly 33.87 degrees south. In late June, the shortest days of the southern-hemisphere winter, Fajr falls noticeably later and Maghrib noticeably earlier than in December's long summer days. That's the opposite pattern to what a northern-hemisphere calendar would show for the same months. See the Southern-Hemisphere Prayer Times guide for what that inversion changes in practice.
Real astronomy, not guesswork
Computed fresh, every time
Jean Meeus's own algorithms
The same solar-position formulas used in general-purpose astronomy software, not a simplified prayer-app shortcut.
Computed live, not looked up
Every time runs fresh against real coordinates, rather than being pulled from a static yearly table.
Never interpolated
Nothing here is borrowed from a nearby city or copied from a static yearly PDF.
Accurate in any of Sydney's 139 suburbs
The same formula runs for each suburb's own coordinates, not one CBD figure applied everywhere.
Frequently Asked Questions
Is prayer time calculation based on the actual sun or a fixed schedule? +
The actual sun. Every time is derived from the sun's real angle below or above the horizon for a specific date, latitude and longitude, recalculated fresh rather than looked up from a fixed yearly table.
Who created the formulas used to calculate prayer times? +
The underlying solar-position mathematics comes from Jean Meeus, an astronomer whose published algorithms for calculating the sun's position are the standard reference implemented by most prayer-time software.
Why isn't Dhuhr just always at 12 noon? +
Dhuhr begins when the sun passes its highest point for that specific day and location. That's solar noon, not clock noon. Solar noon drifts a few minutes either side of 12:00 through the year and differs by location within a timezone.