7.4.1 Times

Functions for conversion of time values between various forms. The forms used are

Modified Julian Date (MJD)

A continuous measure in days since midnight at the start of 17 November 1858. Based on UTC.

ISO 8601

A string representation of the form yyyy-mm-ddThh:mm:ss.s, where the T is a literal character (a space character may be used instead). Based on UTC.

Julian Epoch

A continuous measure based on a Julian year of exactly 365.25 days. For approximate purposes this resembles the fractional number of years AD represented by the date. Sometimes (but not here) represented by prefixing a 'J'; J2000.0 is defined as 2000 January 1.5 in the TT timescale.

Besselian Epoch

A continuous measure based on a tropical year of about 365.2422 days. For approximate purposes this resembles the fractional number of years AD represented by the date. Sometimes (but not here) represented by prefixing a 'B'.

Therefore midday on the 25th of October 2004 is 2004-10-25T12:00:00 in ISO 8601 format, 53303.5 as an MJD value, 2004.81588 as a Julian Epoch and 2004.81726 as a Besselian Epoch.

Currently this implementation cannot be relied upon to better than a millisecond.

isoToMjd( isoDate )

Converts an ISO8601 date string to Modified Julian Date. The basic format of the isoDate argument is yyyy-mm-ddThh:mm:ss.s, though some deviations from this form are permitted:

• The 'T' which separates date from time can be replaced by a space
• The seconds, minutes and/or hours can be omitted
• The decimal part of the seconds can be any length, and is optional
• A 'Z' (which indicates UTC) may be appended to the time

Some legal examples are therefore: "1994-12-21T14:18:23.2", "1968-01-14", and "2112-05-25 16:45Z".

• isoDate (String): date in ISO 8601 format
• return value (floating point): modified Julian date corresponding to isoDate

dateToMjd( year, month, day, hour, min, sec )

Converts a calendar date and time to Modified Julian Date.

• year (integer): year AD
• month (integer): index of month; January is 1, December is 12
• day (integer): day of month (the first day is 1)
• hour (integer): hour (0-23)
• min (integer): minute (0-59)
• sec (floating point): second (0<=sec<60)
• return value (floating point): modified Julian date corresponding to arguments

dateToMjd( year, month, day )

Converts a calendar date to Modified Julian Date.

• year (integer): year AD
• month (integer): index of month; January is 1, December is 12
• day (integer): day of month (the first day is 1)
• return value (floating point): modified Julian date corresponding to 00:00:00 of the date specified by the arguments

mjdToIso( mjd )

Converts a Modified Julian Date value to an ISO 8601-format date-time string. The output format is yyyy-mm-ddThh:mm:ss.

• mjd (floating point): modified Julian date
• return value (String): ISO 8601 format date corresponding to mjd

mjdToDate( mjd )

Converts a Modified Julian Date value to an ISO 8601-format date string. The output format is yyyy-mm-dd.

• mjd (floating point): modified Julian date
• return value (String): ISO 8601 format date corresponding to mjd

mjdToTime( mjd )

Converts a Modified Julian Date value to an ISO 8601-format time-only string. The output format is hh:mm:ss.

• mjd (floating point): modified Julian date
• return value (String): ISO 8601 format time corresponding to mjd

formatMjd( mjd, format )

Converts a Modified Julian Date value to a date using a customisable date format. The format is as defined by the java.text.SimpleDateFormat class. The default output corresponds to the string "yyyy-MM-dd'T'HH:mm:ss"

• mjd (floating point): modified Julian date
• format (String): formatting patttern
• return value (String): custom formatted time corresponding to mjd

mjdToJulian( mjd )

Converts a Modified Julian Date to Julian Epoch. For approximate purposes, the result of this routine consists of an integral part which gives the year AD and a fractional part which represents the distance through that year, so that for instance 2000.5 is approximately 1 July 2000.

• mjd (floating point): modified Julian date
• return value (floating point): Julian epoch

julianToMjd( julianEpoch )

Converts a Julian Epoch to Modified Julian Date. For approximate purposes, the argument of this routine consists of an integral part which gives the year AD and a fractional part which represents the distance through that year, so that for instance 2000.5 is approximately 1 July 2000.

• julianEpoch (floating point): Julian epoch
• return value (floating point): modified Julian date

mjdToBesselian( mjd )

Converts Modified Julian Date to Besselian Epoch. For approximate purposes, the result of this routine consists of an integral part which gives the year AD and a fractional part which represents the distance through that year, so that for instance 1950.5 is approximately 1 July 1950.

• mjd (floating point): modified Julian date
• return value (floating point): Besselian epoch

besselianToMjd( besselianEpoch )

Converts Besselian Epoch to Modified Julian Date. For approximate purposes, the argument of this routine consists of an integral part which gives the year AD and a fractional part which represents the distance through that year, so that for instance 1950.5 is approximately 1 July 1950.

• besselianEpoch (floating point): Besselian epoch
• return value (floating point): modified Julian date

unixMillisToMjd( unixMillis )

Converts from milliseconds since the Unix epoch (1970-01-01T00:00:00) to a modified Julian date value

• unixMillis (long integer): milliseconds since the Unix epoch
• return value (floating point): modified Julian date

mjdToUnixMillis( mjd )

Converts from modified Julian date to milliseconds since the Unix epoch (1970-01-01T00:00:00).

• mjd (floating point): modified Julian date
• return value (long integer): milliseconds since the Unix epoch