DESIGNATE EARTH MERIDIAN

Syntax

Fixed

   DESIGNATE @int(1001:1099)
      CENTER @body
      REFERENCE EARTH MERIDIAN
      (2:3){ LATITUDE  @number
           | LONGITUDE @number
           | @options
           | RADIUS    @number }
      (0:3){ FROM  @calendar
           | TO    @calendar
           | EPOCH @calendar }

Moving

   DESIGNATE @int(1001:1099)
      CENTER @body
      REFERENCE EARTH MERIDIAN
      (2:3){ LATITUDE  (1:2)@number
           | LONGITUDE (1:2)@number
           | @options
           | RADIUS    (1:2)@number }
      EPOCH @calendar
      (0:2){ FROM @calendar
           | TO   @calendar }

Description

When creating a designated object in this system, you must specify the latitude and longitude of the object. The radius is optional, and defaults to the radius of the reference sphere.

Definition

The Earth meridian frame is a spherical coordinate system centered at the reference body. The radius of the reference sphere is the largest semi-major axis of the tri-axial ellipsoid used to model the body. The equator of the frame contains the sub-solar and sub-Earth points on the reference sphere. The reference meridian (zero degrees longitude) of the frame contains the sub-Earth point.

By definition, the portion of the limb illuminated by the sun is at 270 degrees longitude. The dark portion of the limb is at 90 degrees longitude.

Examples

The following designated object moves along the lit limb of Io.

   DEFINE LIMB_SCAN 1001;
 
   DESIGNATE LIMB_SCAN
   CENTER IO
   REFERENCE EARTH MERIDIAN
             LONGITUDE  270 DEGREES
             LATITUDE   -45 DEGREES 5 DEGREES/HOUR
             EPOCH 1 OCT 1990 12:00:00
             FROM  1 OCT 1990  3:00:00
             TO    1 OCT 1990 21:00:00 ;