The plot shows the airmass of all candidate objects as a function of
hour angle and updates automatically every 15 seconds.  For reference,
the right ascension is also plotted on the top.  The plot axes are color
coded by time of day.  If the sun is above the horizon, the plot axes
are yellow.  You also see the time to sunset display in the box just below
the time.  The time of sunset should be good to a few minutes.  The axes
are light brown during civil twilight (CT).  The axes switch to light
purple during nautical twilight (NT).  Then, during astronomical twilight
the axes are a darker purple.  During the night, the axes plot as white.
If either the sun or moon are high enough in the sky, they will appear on
the plot as a large yellow and white filled circle, respectively.  The altitude
of the sun an moon are shown in the box below the time along with the phase
of the moon on its line.

In the middle of the night you will see three vertical lines on the plot.
The lines are dark cyan on the left and right with a purple line in the middle.
The purple line denotes the locate in the sky that is directly opposite of
the Sun, or the opposition point.  The rates of motion for the objects will
be highest when they are near this line.  The cyan lines marked the location
30 degrees ahead and behine the opposition point.  If you wish to combine
search observations with recovery operations, you must work between these two
lines.  The yellow arcing line on the plot shows the ecliptic.

The objects are plotted with various symbols and colors.  The objects shown
complement the information in the top right information box.  Total fields
are the total number that satisfy the selection criteria.  Any candidate object
that has not yet been observed plots as a white hollow diamond.  Some objects
are shown as hollow purple diamons.  These objects are valid to observe but the
rate of motion is slow enough that you must wait for the next night to do the
second image.  Clearly, if you have a one-night observing run these objects are
not really useful candidates.  The sum of white and purple diamonds are counted
for the "Available Fields" number.

Objects that have been done once are plotted as blue triangles.  These are
counted as "In Progress Fields".  This type of object also shows the distance
it has moved since the first frame in the box with the RA, DEC, and HA.
Once the object has moved farther than "MinSep", it plots with a small red
dot in the center.  This provides a visual clue that the object is ready
for the second pass.  Note that if you click the "Field" button, the program
will automatically select the western-most object that is ready for pass 2.
If there are no such objects to select, the selection is not changed.

Note that if you select "Pass 1", you only see those objects tagged as
"available".  If you select "Pass 2", you only see those objects that have
been observed once.  Selecting "All" lets you see both at the same time.
