PRO DAYCNV, XJD, YR, MN, DAY, HR
;+
; NAME:
;	DAYCNV
; PURPOSE:
;	Converts julian dates to gregorian calendar dates
;
; CALLING SEQUENCE:
;	DAYCNV, XJD, YR, MN, DAY, HR
;
; INPUTS:
;	XJD = Julian date, double precision scalar or vector
;
; OUTPUTS:
;	YR = Year (Integer)
;	MN = Month (Integer)
;	DAY = Day (Integer)
;	HR = Hours and fractional hours (Real).   If XJD is a vector,
;		then YR,MN,DAY and HR will be vectors of the same length.
;
; EXAMPLE:
;	IDL> DAYCNV, 2440000.D, yr, mn, day, hr    
;
;	yields yr = 1968, mn =5, day = 23, hr =12.   
;
; WARNING:
;       Be sure that the julian date is specified as double precision to
;       maintain accuracy at the fractional hour level.
;
; REVISION HISTORY:
;       Converted to IDL from Yeoman's Comet Ephemeris Generator, 
;       B. Pfarr, STX, 6/16/88
;-
 On_error,2

 if N_params() lt 2 then begin
    print,"Syntax - daycnv, xjd, yr, mn, day, hr
    print,'  Julian date, xjd, should be specified in double precision
    return
 endif

 sz = size(xjd)

; Adjustment needed because Julian day starts at noon, calender day at midnight

 jd = long(xjd)                         ;Truncate to integral day
 frac = double(xjd) - jd + 0.5          ;Fractional part of calender day
 after_noon = where(frac ge 1.0, Next)
 if Next GT 0 then begin                ;Is it really the next calender day?
      frac(after_noon) = frac(after_noon) - 1.0
      jd(after_noon) = jd(after_noon) + 1
 endif
 hr = frac*24.0
 l = jd + 68569
 n = 4*l / 146097l
 l = l - (146097*n + 3l) / 4
 yr = 4000*(l+1) / 1461001
 l = l - 1461*yr / 4 + 31        ;1461 = 365.25 * 4
 mn = 80*l / 2447
 day = l - 2447*mn / 80
 l = mn/11
 mn = mn + 2 - 12*l
 yr = 100*(n-49) + yr + l
 return
 end