Keith's astrolabes: description and use of the prayer lines displayed with my Java applet
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Prayer Lines

Prayer lines can be shown on the traditional astrolabe plate. They cannot be shown on the equinoctial, universal or spherical astrolabe displays.
In medieval times, the curves known as Prayer Lines were used by Moslems to find two of the five times of prayers during the day.

The five prayer times were nominally at sunset, nightfall (evening twilight), daybreak (morning twilight), after midday and the middle of the afternoon. During medieval times, the prayer lines on the traditional astrolabe indicated the latter two times of prayer.

By repeatedly pressing the '3' on the keyboard, you can display these two curves below the horizon, above and below the horizon, or you can omit them. You can also select these options using the menu:

Menu: Astrolabe /Front - Prayer Lines
To use the Prayer Lines, you must first find the position of the Sun on the ecliptic circle and rotate the rete to the position relating to the current date and time. When the Sun's position is over a prayer line drawn above the horizon arc, it indicates the time for prayer. If the prayer lines are only shown below the horizon arc, the point on the ecliptic circle is used which is diametrically opposite the point where the Sun is located.

The time of the first prayer of the day is indicated by the point at which the setting Sun is on the horizon. The times of the other two prayers were probably indicated by the 18 degree twilight line or, where this was not shown, by the 18 degree almucantar in conjunction with the point diametrically opposite the position of the Sun on the ecliptic circle.

Further details can be found in sections I and V of:

King, D.A, (1993). Astronomy in the Service of Islam.
  - Published in Aldershot (UK) by Variorum.

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Copyright Keith Powell 1999-2002