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unusually large telescope.  These catalogs were assembled because if
you study enough of them, it is possible to determine information about
the size and age of the universe.  The Zwicky catalog lists 9,134
clusters in the northern sky. The Abell catalog lists over 5,000
clusters in all parts of the sky. Don't confuse the Abell catalog of
clusters of galaxies with the Abell catalog of planetary nebulae (p. 12).

   One can also find a galaxy by its Hickson designation. The Hickson
catalog lists 100 compact clusters of galaxies, similar to Copeland's
Septet and other close groupings.  The Hickson designation consists
of a number from 1 to 100,  followed by a letter;  for example,
Hickson 42E would be the fifth galaxy found in cluster #42.
                                                                 
   The Arp catalog contains "peculiar" galaxies and groups of galaxies
listed by Halton Arp.  Many of these objects make for interesting
observing with small telescopes. Their numbers run from 1 to 338.

5c:  Finding nebulae          

   When you click on the "Nebula" option in the "Go to" menu, you will
get the following menu:

Sharpless
Lynd's Bright Neb
PK (Strasbourg)
Van den Bergh
Barnard Dark Neb
Common Name
Abell Planetary
                                                                
   To find an object by its Sharpless,  Lynd's Bright Nebula, Abell,
van den Bergh,  or Barnard number,  click on the option and type in
the catalog number;  Guide will recenter on that object.

   By the way,  don't confuse the Abell catalog of planetary nebulae
with the Abell catalog of clusters of galaxies (p. 11).
                                                                       
   The PK (Perek-Kohoutek),  or Strasbourg catalog of nebulae,
requires a pair of numbers.  (These numbers actually form a coordinate
for the object.)  For this option,  you enter both numbers,  as in
"249-5.1" or "215+11.1".  The numbers will be separated by either a
plus or minus sign.

   Most nebulae are known by their common names,  such as the Eskimo
nebula or the Trifid nebula.  The "Common Name" menu provides a list
of these names from which to choose.

5d:  Entering coordinates          

   Guide has provisions for entering coordinates in five different
systems:  equatorial (RA/dec),  ecliptic,  galactic,  supergalactic,

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