The DATE_
  constants are defined and they offer standard
  date representations, which can be used along with the date format functions
  (like date()).
 
Following constants specify a format returned by functions date_sunrise() and date_sunset().
SUNFUNCS_RET_TIMESTAMP
     (int)
   SUNFUNCS_RET_STRING
     (int)
   SUNFUNCS_RET_DOUBLE
     (int)