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immediately result in the usual brief summary of data concerning Mars.

   When you click on a solar system object,  the Add A Trail and Make
Ephemeris options are not gray any more:  you can make a trail or
ephemeris for that object now.  If you click on a non-solar system
object, you can't make a trail or ephemeris,  and these two options
remain grayed out.
                                                                       
   Now click on "Add a Trail".  The dialog box provided is a short
one, and asks you to to select the step size and number of steps on
the trail. (For this hundred-day trail,  you might select,  say,
fifty steps of two days apiece.)  There are check-boxes that let you
tell Guide that "index marks" and date/time labels should be added to
this trail,  and controls to set the frequency of the marks and labels.
(In this example,  if you asked for an index mark at every step and
time labels on every fifth,  then Guide would put a little cross-mark,
perpendicular to the trail,  at two-day intervals,  and date/time
labels at ten-day intervals.)

   Also,  you can select the color of the trail;  and for convenience,
there is a "Clear Trails" button to eliminate all of them.  (However,
you can instead right-click on a particular trail and tell Guide to
delete it, or to change its color.)

   Once this setup work is done,  you can click the "Add Trail" button,
and Guide will pause briefly to compute and display the trail in question.

   Guide will automatically save your trails when you exit the
program,  and will bring them back up when you restart the program.
The trails are stored as an overlay,  which means you can control
their display in the Overlay menu.  You can add text,  lines,  and
circles to the trails,  select the fields of view where they can be
shown,  and remove unwanted objects;  see the section on user
overlays on page 35.
                                                         
   The steps for creating an ephemeris for a solar system object are
very similar to those for creating a trail.  As before,  set the
current time to match the start of the ephemeris,  and right-click
on the object for which you want an ephemeris.  Click on "Make
Ephemeris", and enter the number of steps and their size.  Click OK,
and Guide will compute the ephemeris and display it on-screen.  You
can save the ephemeris to a file or print it,  much as you could any
other help/glossary/"more info" item.
                                                 
   By default,  Guide will provide some fairly useful data in the
ephemerides,  but you may want to provide different details.  For
example,  for an artificial satellite,  the alt/az may be of greater
interest than the RA/dec;  or you may want to list the percent of an
object that is illuminated.  In such cases,  it helps to click on the
"Options..." button in the "Make Ephemeris" dialog. This leads to a
set of check-boxes for every item that can be shown in an ephemeris.

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