Name

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      GET_DATE

Purpose

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      Return the (current) UTC date in CCYY-MM-DD format for FITS headers

Explanation

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      This is the format required by the DATE and DATE-OBS keywords in a
      FITS header.

Calling Sequence

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      GET_DATE, FITS_date, [ in_date, /OLD, /TIMETAG ]

Optional Inputs

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      in_date - string (scalar or vector) containing dates in IDL
            systime() format (e.g. 'Tue Sep 25 14:56:14 2001')

Outputs

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      FITS_date = A scalar character string giving the current date. Actual
              appearance of dte depends on which keywords are supplied.
     
      No Keywords supplied - dte is a 10 character string with the format
              CCYY-MM-DD where <CCYY> represents a calendar year, the
              ordinal number of a calendar month within the calendar year,
              and <DD> the ordinal number of a day within the calendar month.
      /TIMETAG set - dte is a 19 character string with the format
              CCYY-MM-DDThh:mm:ss where <hh> represents the hour in the day,
                <mm> the minutes, the seconds, and the literal 'T' the
              ISO 8601 time designator
      /OLD set - dte is an 8 character string in DD/MM/YY format

Input Keywords

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      /TIMETAG - Specify the time to the nearest second in the DATE format
      /OLD - Return the DATE format formerly (pre-1997) recommended for FITS
              Note that this format is now deprecated because it uses only
              a 2 digit representation of the year.

Example

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      Add the current date to the DATE keyword in a FITS header,h
   
      IDL> GET_DATE,dte
      IDL> sxaddpar, h, 'DATE', dte, 'Date header was created'

Notes

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      (1) A discussion of the DATExxx syntax in FITS headers can be found in
      http://www.cv.nrao.edu/fits/documents/standards/year2000.txt
      (2) Those who wish to use need further flexibility in their date
      formats (e.g. to use TAI time) should look at Bill Thompson's time
      routines in http://sohowww.nascom.nasa.gov/solarsoft/gen/idl/time

Procedures Used

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      DAYCNV - Convert Julian date to Gregorian calendar date

Revision History

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      Written W. Landsman March 1991
      Major rewrite to write new DATExxx syntax W. Landsman August 1997
      Converted to IDL V5.0 W. Landsman September 1997
      Work after year 2000 even with /OLD keyword W. Landsman January 2000
      Don't need to worry about TIME_DIFF since V5.4 W. Landsman July 2001
      Assume since V5.4, remove LOCAL_DIFF keyword W. Landsman April 2006