pro month_start_end,yr,st_day,en_day,st_date,en_date

;------------------------------------------------------------------------------
; 
; Purpose:
;   Convert month,day,year into julian date,  and character date
;
; Input:
;   yr     = year (e.g., 1993 or 93)
;
; Output:
;   st_day....start day of month (i.e., day of year (1-365), arr(12)
;   en_day....last day of month
;   st_date...start date of month (i.e., yyyydoy), arr(12)
;   en_date...end date of month
;
; Source: Mark Hervig
;
;------------------------------------------------------------------------------

   dayoff = [0,31,59,90,120,151,181,212,243,273,304,334,365]

   st_day  = lonarr(12)
   en_day  = lonarr(12)
   st_date = lonarr(12)
   en_date = lonarr(12)

   yyyy = yr

;- look for 2 digit years

   if (yr le  99 and yr gt 50) then yyyy = 1900+yr
   if (yr le  50) then yyyy = 2000 + yr
   
;- adjust for leap year

   leapyr = yyyy - long(yyyy/4) * 4

   for i = 0,12 do if (leapyr eq 0 and i ge 2) then dayoff(i)=dayoff(i)+1 

;- find month start end days

   for i = 0,11 do begin
   
     d1 = dayoff(i  ) + 1  
     d2 = dayoff(i+1)
     st_day(i) = d1
     en_day(i) = d2
     st_date(i) = yyyy*1000L + d1
     en_date(i) = yyyy*1000L + d2
    
   endfor
  
  return
  end