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and edit the file NGC.NOT in your Guide directory.

   You'll see that a few notes have been added already,  mostly telling
you what supernovae have appeared in which galaxy. This is admittedly
not very crucial data;  it's supplied mostly to give an idea as to how
the system works.  You'll also see that some notes have already been
supplied for NGC 253. Try extending that text to read something like:

~~253
   The ^supernova^ 1940E was found in this galaxy on
1940 Nov 22 at RA 00 45.1, declination -25 34 (epoch
B1950), magnitude 14.0.
   On 23 Aug 1997,  I observed this galaxy with a 10"
f/4 Newtonian and saw that...

   Of course,  you can add remarks for new objects by inserting
"tilde-number"s for them.  There are similar files for a variety of
other objects:  IC.NOT,  UGC.NOT,  ASTEROID.NOT,  and
PLANETS.NOT.  The system has to be modified in cases such as
COMET.NOT and PK.NOT;  you'll see that these files use a tilde-
plus-name system,  since tilde-plus-number would not be very helpful.

   The system can even be extended to cover datasets you have added to
Guide with the user-added dataset system; see page 68 for
details.

23: ABOUT GUIDE'S DATA           

   As has been mentioned,  Guide draws its data from a number of
sources.  It can be helpful to know something about these sources: their
limits,  purposes,  and uses.  This chapter will discuss these issues.
                                                                
   For stars brighter than about mag 11,  Guide uses the Hipparcos and
Tycho Catalogs.  These catalogs were both generated by the European
Space Agency (ESA) Hipparcos satellite,  and are often spoken of as if
they were essentially identical.  They are not, and in some cases,  the
differences can be very significant!

   The Hipparcos catalog contains 118 218 stars that were primary
targets for observation.  Most are bright stars,  but a few dimmer stars
that were of special interest were included: mostly nearby stars and
some variables.  The satellite gathered positions to a precision of
about .001 arcsecond,  and highly precise proper motions,  parallax
(distance) data,  and magnitudes in visual and "blue" systems,  for
these stars. (Some were more precise,  some less so;  the specific data
for each star is listed when you ask for "More Info" about it.)
                                                            
   The Tycho catalog contains a total of over 2.5 million stars.  (Tycho
has been released in two versions:  Tycho-1 had about 1 million stars,
but the data was reprocessed to detect fainter objects,  and the
current Tycho-2 catalog has about 2.5 million stars.)  Tycho attempts

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