 example, the string

                 'Lt + s'

               is valid.

      obsrvr   is the name of the observing body. The observing body
               is an ephemeris object: it typically is a spacecraft,
               the earth, or a surface point on the earth. `obsrvr' is
               case-insensitive, and leading and trailing blanks in
               `obsrvr' are not significant. Optionally, you may
               supply a string containing the integer ID code for
               the object. Fo