PRO JULDATE, DATE, JD, PROMPT = prompt ;+ ; NAME: ; JULDATE ; PURPOSE: ; Convert from calendar to Reduced Julian Date ; ; EXPLANATION: ; Julian Day Number is a count of days elapsed since Greenwich mean noon ; on 1 January 4713 B.C. The Julian Date is the Julian day number ; followed by the fraction of the day elapsed since the preceding noon. ; ; This procedure duplicates the functionality of the JULDAY() function in ; in the standard IDL distribution, but also allows interactive input and ; gives output as Reduced Julian date (=JD - 2400000.) ; CALLING SEQUENCE: ; JULDATE, /PROMPT ;Prompt for calendar Date, print Julian Date ; or ; JULDATE, date, jd ; ; INPUT: ; DATE - 3 to 6-element vector containing year,month (1-12),day, and ; optionally hour, minute, and second all specified as numbers ; (Universal Time). Year should be supplied with all digits. ; Years B.C should be entered as negative numbers (and note that ; Year 0 did not exist). If Hour, minute or seconds are not ; supplied, they will default to 0. ; ; OUTPUT: ; JD - Reduced Julian date, double precision scalar. To convert to ; Julian Date, add 2400000. JULDATE will print the value of ; JD at the terminal if less than 2 parameters are supplied, or ; if the /PROMPT keyword is set ; ; OPTIONAL INPUT KEYWORD: ; /PROMPT - If this keyword is set and non-zero, then JULDATE will prompt ; for the calendar date at the terminal. ; ; RESTRICTIONS: ; The procedure HELIO_JD can be used after JULDATE, if a heliocentric ; Julian date is required. ; ; EXAMPLE: ; A date of 25-DEC-2006 06:25 UT may be expressed as either ; ; IDL> juldate, [2006, 12, 25, 6, 25], jd ; IDL> juldate, [2006, 12, 25.2673611d], jd ; ; In either case, one should obtain a Reduced Julian date of ; JD = 54094.7673611 ; ; PROCEDURE USED: ; GETOPT() ; REVISION HISTORY ; Adapted from IUE RDAF (S. Parsons) 8-31-87 ; Algorithm from Sky and Telescope April 1981 ; Added /PROMPT keyword, W. Landsman September 1992 ; Converted to IDL V5.0 W. Landsman September 1997 ; Make negative years correspond to B.C. (no year 0), work for year 1582 ; Disallow 2 digit years. W. Landsman March 2000 ;- On_error,2 if ( N_params() EQ 0 ) and ( ~keyword_set( PROMPT ) ) then begin print,'Syntax - JULDATE, date, jd or JULDATE, /PROMPT' print, \$ ' date - 3-6 element vector containing [year,month,day,hour,minute,sec]' print,' jd - output reduced julian date (double precision)' return endif if ( N_elements(date) EQ 0 ) then begin opt = '' rd: read,' Enter Year,Month,Day,Hour, Minute, Seconds (All Numeric): ',opt date = getopt( opt, 'F' ) endif case N_elements(date) of 6: 5: date = [ date, 0.0d] 4: date = [ date, 0.0d,0.0d] 3: date = [ date, 0.0d, 0.0d,0.0d] else: message,'Illegal DATE Vector - must have a least 3 elements' endcase iy = floor( date[0] ) if iy lt 0 then iy++ else \$ if iy EQ 0 then message,'ERROR - There is no year 0' im = fix( date[1] ) date = double(date) day = date[2] + ( date[3] + date[4]/60.0d + date[5]/3600.0d) / 24.0d ; if ( im LT 3 ) then begin ;If month is Jan or Feb, don't include leap day iy-- & im = im+12 end a = long(iy/100) ry = float(iy) jd = floor(ry*0.25d) + 365.0d*(ry -1860.d) + fix(30.6001d*(im+1.)) + \$ day - 105.5d ;Gregorian Calendar starts on Oct. 15, 1582 (= RJD -100830.5) if jd GT -100830.5 then jd = jd + 2 - a + floor(a/4) if N_params() LT 2 || keyword_set( PROMPT) then begin yr = fix( date[0] ) print, FORM='(A,I4,A,I3,A,F9.5)',\$ ' Year ',yr,' Month', fix(date[1] ),' Day', day print, FORM='(A,F15.5)',' Reduced Julian Date:',JD endif return end ; juldate