FIND PHASE

Syntax

   FIND @name PHASE
 
        (2:2){ OF   @body
             | FROM @body  }
 
        (1:1){ GREATER THAN           @number
             | LESS THAN              @number
             | EQUAL TO               @number
             | BETWEEN  @number AND   @number
             | ABSOLUTE MINIMUM PLUS  @number(0:)
             | ABSOLUTE MAXIMUM MINUS @number(0:)
             | ABSOLUTE MINIMUM
             | ABSOLUTE MAXIMUM
             | LOCAL    MINIMUM
             | LOCAL    MAXIMUM  }
 
        (0:1){ WITHIN @name }
 
        STEP SIZE @number(0:)

Description

This command locates intervals during which the phase (observer-target-Sun) angle OF a target body as seen FROM an observing body satisfies a specified constraint.

Examples

Example 1

In the following example, the FIND PHASE command is used to locate intervals during which the phase of an asteroid is greater than 90 degrees.

   FIND PHASE_NEAR_90 PHASE OF ASTEROID
        FROM EARTH GREATER THAN 80 DEGREES
        STEP SIZE 3 WEEKS;

Example 2

In the following example, the FIND PHASE command is used to locate intervals when the phase of Phobos is at a local maximum. The search interval is restricted to intervals (determined previously) when Phobos is not occulted by, eclipsed by, or in transit across Mars.

   IMPORT  PHOBOS_CLEAR.WIN AS CLEAR;
 
   FIND MAX_PHASE PHASE OF PHOBOS
        FROM EARTH LOCAL MAXIMUM,
        WITHIN CLEAR
        STEP SIZE 15 MINUTES;
 
   LET NEAR_MAX_PHASE = MAX_PHASE EXPANDED
                        LEFT  30 MINUTES
                        RIGHT 30 MINUTES;

Notes

The phase of an object is always between 0 and 180 degrees. The phase of the outer planets and their satellites is generally near zero.