MJD
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Contents: Description, Arguments, Usage, Examples, Sub-Functions, Related Functions, Source Supported Under Version: > 1.14
Description Converts input date and time to UTC Modified Julian Date
Arguments and Return Values Parameters: Numeric arrays specifying the year, month, day, hour, minute, second, time zone offset, and calendar mode. The calendar mode must be passed by reference, with the name cal. Return Value: A double-format numeric array with the same organization as the inputs
Usage Syntax: MJD(year, month, day, hour, minute, second, time zone offset, cal=n) or MJD(clock(1), cal=n) The Modified Julian Date is a continuous count of days since midnight UTC at the beginning of November 17, 1858 (in the Gregorian calendar). The inputs specifying year, month, day, hour, minute, second, and time zone offset must be in that order. They can be scalar, or they can be (multi-element) arrays. Scalars and arrays can be mixed, but any arrays used must have the same dimensions. Time zone offset is (local time in hours) - (UTC time in hours). Most time zone offsets are integers. Eastern Standard Time is -5, and Mountain Standard Time is -7. The time zone offset is assumed to be zero (UTC) if not specified. The only required input is the year. Any omitted parts of the date are set to one, and the time, if omitted, defaults to midnight (UTC) at the beginning of the input date. Thus MJD(2009) returns the Modified Julian Date of midnight UTC on January 1, 2009. If the hour is given but minutes and seconds are omitted, minutes and seconds default to zero. If the hour and minute are given but seconds are omitted, seconds default to zero. For years before 1, use astronomical numbering, e.g. 4713 BCE = -4712. (There was no year 0.) This function also accepts date and time arrays in the format returned by the clock function. To quickly get the current Modified Julian Date, enter MJD(clock(1)). If the calendar mode is specified, it must be passed by reference, with the name cal and a value of 0 or 1. All other inputs should be passed by value. (See the examples.) If the calender mode is omitted, the function will guess, based on the latest input date. For (latest) input dates between October 15, 1582 and December 31, 1919 (when both calendar systems were in use), the function will print a warning about guessing the calendar mode. (Latest) dates before October 15, 1582 use the Julian calendar. (Latest) dates after that use the Gregorian (modern) calendar. This reflects the first changeover date. However, different countries changed at different times. See http://www.tondering.dk/claus/cal/node3.html The function cannot switch modes midway - it will compute using one calendar system OR the other for ALL members of an input array. If you want to find some MJD's for some dates in the Julian calendar and some in the Gregorian calendar, you must enter them separately (that is, first enter the dates from the Julian calendar, then enter the dates from the Gregorian calendar, specifying modes). The formulae used here are from http://en.wikipedia.org/wiki/Julian_day and have been checked extensively against USNO calculator at http://aa.usno.navy.mil/data/docs/JulianDate.php The returned value is an integer if only the date (no time) is input. It is a double if any part of the time is input. When MJD() is entered without any arguments, it prints its description, as shown below.
Examples dv> MJD() Convert input date and time to UTC Modified Julian Date MJD(year, month, day, hour, minute, second, time zone offset, cal=n) or MJD(clock(1), cal=n) returns the Modified Julian Date (number of days since midnight UTC at the beginning of November 17, 1858). The dates/times must be entered in the given order. For BCE, use astronomical year numbering, e.g. 4713 BCE = -4712 Works for array inputs cal (sets calendar mode) must be passed by reference cal=0 for Julian calendar; cal=1 for Gregorian (modern) calendar If cal is omitted, the function will guess, based on the date. (Latest) dates before October 15, 1582 use Julian calendar (Latest) dates after that use Gregorian calendar This reflects the first changeover date. However, different countries changed at different times. See http://www.tondering.dk/claus/cal/node3.html The function cannot switch modes midway - it will compute using one calendar system OR the other for ALL members of an input array. If you want to find some MJD's for some dates in the Julian calendar and some in the Gregorian calendar, you must enter them separately (e.g. first enter the dates from Julian calendar, then enter the dates from the Gregorian calendar, specifying modes). Returns double-precision Modified Julian Date if given date and time, integer Modified Julian Day Number if only given date Uses function JD for integer JDN calculation, then subtracts This function therefore returns more precise values than JD for modern dates, although the difference is unimportant for most applications. S.Marshall 04-10-2009 0 dv> MJD(2009) 54832 dv> MJD(2009, 1) 54832 dv> MJD(2009, 1, 1) 54832 dv> MJD(2009, 1, 1, 12) 54832.5000000000 dv> MJD(2009, 1, 1, 12, 0, 0, -7) 54832.7916666667 dv> clock(1) 7x1x1 array of double, bsq format [56 bytes] 2009.00000000000 12.0000000000000 15.0000000000000 12.0000000000000 49.0000000000000 38.7224850000000 -7.0000000000000 dv> MJD(clock(1)) 55180.8261556510 dv> a = create(12, start=1) 12x1x1 array of int, bsq format [48 bytes] 1 2 3 4 5 6 7 8 9 10 11 12 dv> MJD(2009, a, 1, 12) 12x1x1 array of double, bsq format [96 bytes] 54832.5000000000 54863.5000000000 54891.5000000000 54922.5000000000 54952.5000000000 54983.5000000000 55013.5000000000 55044.5000000000 55075.5000000000 55105.5000000000 55136.5000000000 55166.5000000000 dv> MJD(2009, a, 15, 12) 12x1x1 array of double, bsq format [96 bytes] 54846.5000000000 54877.5000000000 54905.5000000000 54936.5000000000 54966.5000000000 54997.5000000000 55027.5000000000 55058.5000000000 55089.5000000000 55119.5000000000 55150.5000000000 55180.5000000000 dv> MJD(1918, 11, 11) Assuming Gregorian calendar 21908 |
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Recent Library Changes Created On: 11-18-2009 |
