FIND ORBITAL LONGITUDE

Syntax

   FIND @name ORBITAL LONGITUDE
 
        (2:2){ OF   @body
             | FROM @body  }
 
        BETWEEN @number AND @number
 
        (0:1){ WITHIN @name }
 
        STEP SIZE @number(0:)

Description

This command locates intervals during which the orbital longitude OF a target satellite as seen FROM an observing body lies BETWEEN a pair of specified values.

The definition of orbital longitude for a satellite, is different from the definition used for a planet, asteroid or comet. The definitions below are provided by Dr. Harold Weaver of STScI:

Orbital Longitude of a Satellite

Orbital Longitude for Planets, Asteroids and Comets

Take the vector that points from the apparent center of the sun to the center of the observing body. Project that vector onto the instantaneous orbital plane of the planet(asteroid, comet). This projected vector is the reference axis for the orbital longitude definition.

Note that orbital longitudes of satellites (as seen from Earth) increase with time. Orbital longitudes of inferior planets also increase with time. However, orbital longitude of superior planets (as seen from Earth) decrease with time. The same will be true of most asteroids. For objects that cross the earths orbit their orbital longitudes may increase at some points in their orbits and decrease at other points.

Examples

In the following example, the FIND ORBITAL LONGITUDE command is used to locate intervals during which the orbital longitude of Io is near 90 or 270 degrees (near its maximum angular separation from the planet).

   FIND EAST ORBITAL LONGITUDE OF IO
        FROM EARTH is BETWEEN 80 DEGREES AND 100 DEGREES
        STEP SIZE 0.8 HOURS;
 
   FIND WEST ORBITAL LONGITUDE OF IO
        FROM EARTH  BETWEEN 260 DEGREES AND 280 DEGREES
        STEP SIZE 0.8 HOURS;

Notes

The order of the values following the keyword BETWEEN is significant. For example,

   BETWEEN 10 DEGREES AND 50 DEGREES

refers to an arc of 40 degrees, while

   BETWEEN 50 DEGREES AND 10 DEGREES

refers to an arc of 320 degrees.