FIND ECLIPSE

Syntax

   FIND @name (0:1){ UMBRAL
                   | PENUMBRAL } ECLIPSE
 
                (3:3){ OF   @body
                     | BY   @body
                     | FROM @body }
 
                (0:1){ WITHIN @name }
 
                STEP SIZE @number(0:)

Description

This command locates intervals during which the eclipse OF a target body BY a second body is visible FROM an observing body.

The left endpoint of each interval represents the beginning of a particular eclipse; the right endpoint represents the end of the same eclipse. (Of course, if the search interval begins or ends during an eclipse, the first or last interval will not contain a complete event.)

Each of the eclipsed and eclipsing bodies is represented by a sphere whose radius is equal to the longest equatorial radius of the tri-axial ellipsoid used to model it.

An eclipse is defined to begin when the observer would see the limb of the eclipsed sphere enter the umbra or penumbra of the eclipsing sphere. The eclipse ends when the last part of the limb of the eclipsed body would be observed to leave the umbra or penumbra of the eclipsing sphere.

Both penumbral and umbral eclipses may be specified. If no preference is specified, the program looks for umbral eclipses.

Examples

Example 1

In the following example, the FIND ECLIPSE command is used to locate intervals when Io is eclipsed by Jupiter as seen from Earth. The search interval is restricted to intervals (determined previously) when Jupiter is more than 50 degrees from the Sun.

   IMPORT  JUPITER_50_DEGREES.WIN AS JUP_CLEAR;
 
   FIND IO_ECL ECLIPSE OF IO
                       BY JUPITER
                       FROM EARTH
                       WITHIN JUP_CLEAR
                       STEP SIZE 30 MINUTES;

Because neither UMBRAL nor PENUMBRAL is specified, the program searches for umbral eclipses.

Example 2

In the following example, the FIND ECLIPSE command is used to detect intervals when the shadow of Io is visible on Jupiter---that is, when Jupiter is `eclipsed' by Io.