1 This is used for display only. This will not change the longitude and latitude required for proper zmanim calculation. Please look up proper values for the other fields before generating the calendar. 2 The year is used to ensure correct start and end of daylight savings time. It will also add February 29th on a leap year. Note: The calculation of zmanim remain almost identical from year to year (with a drop of a change for the 1/4 day difference mostly fixed by the leap year every 4th year) using the USNO algorithm, so the calendar can be used for any year. The NOAA algorithm actually adjusts the calculation based on the year and will be more accurate if you set the proper year. 3 You can use Google Maps to select the latitude and longitude for your location. To use this feature, click on the icon to display the map. Use the map controls to get to the desired location and click on it. This will set the longitude and latitude for the point on the map that you clicked. 4 Use negative numbers south of the equator.
Note: For far northern (or southern) locations such as England some zmanim during part of the year such as early calculation of alos in the spring, that by calculation do not occur since the sun never reaches that far below the horizon (and actually calculate to an invalid mathematical value, see JavaDocs of AstronomicalCalendar for more information) will have a value of N/A. 5 Use negative numbers west of the prime meridian (Greenwich). 6 Elevation in Meters above sea level. Negative numbers can not be used. This is used by some sunrise / sunset algorithms to adjust times based on elevation Only sunrise and sunset calculations are adjusted as per Yisroel Vehazmanim and Calendrical Calcuations. It is currently implemented by all algorithms in the Zmanim package using the formula zenith = zenith + Math.toDegrees(Math.acos(earthRadiusInMeters / (earthRadiusInMeters + elevationMeters))) found in Calendrical Calculations. An almost identical algorthm found in Maaglay Tzedek would be to add 0.0347 * squareRoot(elevationMeters) to the zenith. Use 0 to default to the standard algorithms.
Note: Elevation lookup courtesy of Jonathan Stott's earthtools.org elevation webservice. This Elevation data currently only covers the USA and part of Europe. Please see the About the Data section for the coverage map. 7 Locations such as Israel where the start and end of daylight savings time varies from year to year will have an inaccurate start of daylight savings time. I will hopefully soon change the page to allow entry of optional start and end of daylight savings time. 8 The amount of refraction to add to the calculations. Due to refraction the sun can actually be seen before it rises above the horizon. The common calculation is 34' (34 arch minutes of a degree or 34/60). In the Errata and Notes to Calendrical Calculations, a more accurate value of 34.478885263888294' (or 34' 29") is mentioned. The difference is less than 3 seconds. 9 Different algorithms are available for the sunrise / sunset calculations that form the basis for all zmanim calculations. USNO is the US Naval Observatory algorthm. NOAA is the National Oceanic and Atmospheric Administration algorithm. 10 Full returns a complete set of zmanim including 9 calculations for alos. The standard calendar uses the most commonly accepted zmanim.