The sunrise/sunset times, candle-lighting & havdalah times, moon phase information, Jewish holidays, weekly parshiot, and hebrew dates are all calculated programatically. This data is generated using (and subject to the limitations of) two well-known, freely available software packages:
The software packages have been customized for (East) Denver, CO (39°42' latitude, 104°54' longitude -- around Monaco & Alameda), and all displayed times reflect this location. Elevation is not factored into the sunrise/sunset calculations, and certain z'manim are derived (e.g., Havdalah, etc.) using "fixed minutes" calculations, as described below.
Some of the z'manim calculations are configurable. The definitions with the default calculations are as follows:
For all times that depend on a fraction of the day, the day length is calculated from sunrise to sunset. However, for the latest Shema and Tefilah, you may configure either the "Grah" (Vilna Gaon) calculation, using a day that runs from sunrise to sunset, or the "Magen Avraham" calculation, using a day that runs from Alot HaShachar to Tzet Hakochavim. A "proportional hour" is 1/12 of the day (as just described), which is not typically 60 minutes, since the period between sunrise and sunset is rarely exactly 12 hours. The times that refer to "regular" minutes use exact (not proportional) minutes in the calculations.
In addition to the day length calculations, the definitions of Havdalah and Tzet HaKochavim are configurable. (Note: In order for the settings to take effect, you must have cookies enabled in your browser.)
Note: The times are believed to be accurate to within 1-2 minutes, but as
such are to be considered only approximations. No representation or
warranty is provided as to the precision or correctness of the z'manim
calculations. If you ever have any doubts
about the times, it is always best to consult your friendly neighborhood halachic authority.
DO NOT RELY UPON THE SHABBOS Z'MANIM DOWN TO THE LAST MINUTE TO NOT BE MECHALEL SHABBOS!
All customizations and the z'manim calculations were developed by Glenn Zazulia, as was the web interface, based in part on Don Schwartz's www package included with the 'Remind' software.
If you require z'manim information for any given day or location, try www.myzmanim.com or OU.org/holidays/zmanim.