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[As documented in the United States Naval Observatory NOVAS-C 3.0 software package]
2) The user's HTTP client application (browser) must support JavaScript Version 1.2 or later - and have JavaScript enabled.
3) The user's System Clock must be properly set for correct date, time, and time zone - even if the user enters correct values under "Settings". Because AstroClock is a JavaScript application, all calculations are made using the user's System Clock, so it must be set correctly and accurately.
The user may wish to consider running an SNTP ("Simple Network Time Protocol") client application on his or her system to ensure accurate time. If one is not already installed, AboutTime, by Paul Lutus, is an excellent one which I have used for many years and recommend highly. It is freeware (the author calls it "CareWare").
4) "Equation of the Equinoxes", "System Civil Time", "Equation of Time", all left column clock times, and all Julian / Modified Julian Day values are affected by System Clock settings only. AstroClock user Settings have no effect on these values.
5) AstroClock user Settings (as well as System Clock settings) do affect all right column clock times (but not the Julian / Modified Julian Day values).
6) AstroClock user Settings allow the user to specify values for any location, time zone, and/or Daylight Saving Time setting on Earth - including those in which the user's computer is not located.
7) "Longitude" can be entered in any one of the three standard formats: ddd.dddddd (decimal degrees), ddd:mm.mmmmmm (degrees and decimal minutes), ddd:mm:ss.ssssss (degrees, minutes, and decimal seconds). Negative signs are ignored - direction east or west of the prime meridian - which passes through Greenwich, England, UK - is specified using the "E/W" drop-down menu selection control to the right of the "Longitude" text type-in field.
8) The "DST" checkbox indicates whether or not "Daylight Saving Time" (also known as "Summer Time" or "Advanced Time") is in effect. Note that the significance of this checkbox being checked is that Daylight Saving Time is actually in effect - not merely that the location specified observes Daylight Saving Time. It is independent of the System Clock settings.
9) "TZ" is the time zone offset in decimal hours. A negative sign is ignored - direction east or west of the prime meridian (time zone "Zero" or "Z") is specified using the "E/W" drop-down menu selection control to the right of the "TZ" text type-in field. Do not include the effect of Daylight Saving Time in this value as it is specified separately. (For example, New York City should be specified as "5" "W" all year round.) It is independent of the System Clock settings.
10) The user Settings are preloaded for the author's home, located on Little Sebago Lake in Gray, Maine, USA.
2) Astronomical Algorithms, Second Edition, by Jean Meeus
3) The Astronomical Almanac, jointly published by the United States Nautical Almanac Office of the United States Naval Observatory and Her Majesty's Nautical Almanac Office of the United Kingdom Hydrographic Office
4) Explanatory Supplement to the Astronomical Almanac, edited by P. Kenneth Seidelmann
5) The IAU's "Standards of Fundamental Astronomy (SOFA) initiative"
6) A special "thank you" to Dr. Dennis D. McCarthy of the United States Naval Observatory