function: time_ephemeris(t) Purpose: conversion between unix time and ephemeris time Usage: et = time_ephemeris(ut) ; Converts from UT (unix/posix time) to ephemeris time Or: ut = time_ephemeris(et,/et2ut) ; Converts from ephemeris time to UT double precision (UNIX time) Does NOT require the ICY DLM to be loaded Author: Davin Larson