Question: Which Dawn and Dusk times should we follow when reckoning the parameters of day - Astronomical, Nautical, or Civil? What does the Calendar App use?
Answer: Scripture is abundantly clear that a day begins at dawn and ends at dusk. The WLC Calendar Application reckons the parameters of a day by astronomical twilight (dawn/dusk). This is because there is absolutely no trace of sunlight before or after this period. In order to carefully keep the Sabbath day holy, all who love the Sabbath and the Creator will be vigilant to guard these times of transition from dark to light and light to dark that begin and end each day.
According to Scripture, the night is ruled by the moon and stars. Therefore, day begins when the stars disappear, before the actual sunrise, and ends when they appear after sunset.
The moon and stars to rule by night: for His mercy endureth for ever. Psalm 136:9
Thus saith Yahuwah, which giveth the sun for a light by day, and the ordinances of the moon and of the stars for a light by night, which divideth the sea when the waves thereof roar; The Eloah of hosts is his name. Jeremiah 31:35
In some extreme northern/southern locations, astronomical twilight is not always available. When astronomical twilight is not available to determine New Moon Day, the app will default to 4 AM as the twilight time, and a warning symbol will be displayed in all of the subsequent feast days for that lunation. When your mouse is held over this symbol, a message will appear explaining the issue. See image below:
Bear in mind always that while every possible precaution has been taken to ensure the greatest possible accuracy, we must stress that this Luni-Solar Calendar Application is a GUIDE. It is not intended to be a substitute for prayerful study and careful observation.
Note: This particular point may be considered a 'grey area' where we believe some flexibility can be applied. Therefore, where technology is unavailable or personal observation is preferred, the following may be used:
For More on the Biblical Parameters of a Day:
You can learn more about the civil, nautical, and astronomical twilight here: http://aa.usno.navy.mil/faq/docs/RST_defs.php