Configuration of the almanac module is simple - the installer enters the name of the location, selects the location timezone, enters the decimal longitude and latitude, and the desired time output format. Eastern hemisphere longitude and southern hemisphere latitude must be preceded by the minus (-) sign.

The path for the full page output is /almanac. The block can be configured via the normal block configurations page.

Moon rise and set times are calculated using an algorithm outlined in Astronomy On The Personal Computer by Montenbruck and Pfleger. There are several different algorithms that have been published and are available on the web to deal with the complexities of calculating moon rise and set times, and the times calculated by the almanac module may deviate by several minutes from times published in other sources.

What do the various categories of twilight mean? Twilight - the time between dawn and sunrise and also between sunset and dusk, consists of three periods - civil twilight, nautical twilight, and astronomical twilight. Each is defined by the elevation angle of the sun relative to the horizon at the observer's location. Twilight begins or ends when the center of the sun is 6 degrees below the horizon at the observer's location.

If you're interested in the precise definitions you can use any of the many excellent web-based resources that discuss the exact meaning of each period. For those more casually interested:

• Civil Twilight is the brightest phase. People can perform normal outdoor activities, but detailed tasks such as reading usually require some artificial light. The brightest stars and planets can be visible during this period.
• Nautical Twilight marks the period where normal outdoor activities require artificial light, and the general outlines of non-illuminated objects may be barely visible, In the evening, nautical twilight ends when the horizon at sea can no longer be used for navigation; in the morning it starts when the horizon can be used for navigation purposes.
• Astronomical Twilight is the period between nautical twilight and a totally dark sky.

The times in the Rise column on the table above correspond to the beginning times of each phase, from astronomical dawn to sunrise, while in the Set column they correspond to ending times, till astronomical dusk. The row labeled "actual" is the time of sunrise and sunset.