Time Specification

There are three types of time specification:

as a calendar date and optionally time
as a Julian day number
as a numerical expression representing a Julian day number.

Specification as calendar date

The time is expressed as a Julian / Gregorian calendar date followed by an optional time statement. Dates are in the Julian Calendar through 4 October 1582, and then in the Gregorian Calendar, which begins on 15 October 1582. Astronomical dating is used for years before AD 1, so for 1 BC enter 0, for 2 BC –1, for 100 BC -99, etc. Dates between -2999 and +3000 are accepted. If no time statement is given 0:00:00 is assumed. Within a time statement the seconds are optional.

Examples:

Start time and end time are specified as calendar dates with time statements. Ephemeris calculations are performed in intervals of 15 minutes. The start time is specified as a calendar date (January 1, 246 B.C.). As no time statement is given, 0:00 is assumed. 101 ephemeris calculations will be performed in intervals of 1 day, starting -245-01-01. Start time and end time are specified as calendar dates with time statements. 101 ephemeris calculations are performed in intervals of 1/100 of the covered time span. For the meaning of JD1 (end time) and JD0 (start time) see time control script reference)

Specification as Julian day number

The time is expressed as a Julian day number. Julian day numbers between 625673.5 and 2816787.5 are accepted.

Examples:

The start time is specified as a Julian day number. 100 ephemeris calculations are performed in intervals of 2 days. The start time is specified as a Julian day number. The end time is specified as the start time plus 100 days. Ephemeris calculations are performed over a time span of 100 days in intervals of 1 day. For the meaning of JD0 (start time) see time control script reference )

Specification as numerical expression

The expression is representing a Julian day number. Values between 625673.5 and 2816787.5 are accepted. Within the expression all variables, constants, and functions of the time control scripting language may be used (see time control script reference)

Examples:

The start time represents the current time (Now). Ephemeris calculations are performed in intervals of 10 minutes, starting one day (144*10 minutes) before and ending one day after the current time. The start time represents the begin (0:00) of the current day (Today); the end time represents next midnight (Tomorrow). Ephemeris calculations are performed in intervals of 10 minutes. Thus 145 ephemeris data will be calculated (1440/10+1). The start time represents the begin of the current lunar synodic period (last new moon); the end time represents the start of the next synodic period (one synodic period after start time). Ephemeris calculations are performed in intervals of 1 hour. For the meaning of the variables, constants and functions see time control script reference )

Alcyone Ephemeris Documentation
(C) 2007 Alcyone Software