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Observing Guides

The main content of CSOG is the observing guides. Hundreds of them, for thousands of objects.
The guides are intended to be used at the eyepiece of a telescope. Using the guides stargazers will know before, during and after an observation what it is they are looking for, and what it is they are observing. The guides take out the guesswork.

Objects are grouped into Constellation Editions by telescope aperture, Catalog Editions and Observing Programs.

The constellation editions are available in three categories of telescope aperture. These aperture categories are indicative. To observe all of the objects in an edition that matches the aperture of the telescope you use, truly excellent observing conditions may be required.

Constellations Editions

CSOG covers all of the 88 constellations. The constellation of Serpens is divided into separate guides for Serpens Caput and Serpens Cauda.
The Constellation editions are available in three telescope aperture classes, as a rule of thumb:

5-6" Telescopes

  5-6" 8-10" 12"
Carbon stars 217 342 865
Open Clusters 744 (563*) 1356 (910*) 3638 (1544*)
Globular Clusters 160 192 227
Nebulae 186 269 464
Dark Nebulae 103 138 138
Planetary Nebulae 102 180 443
Supernova Remnants 10 17 34
Galaxies 696 1746 7798
Asterisms 63 87 109
Other 4 22 56
Total 2285 4349 13772
* excluding the constellations of Dorado & Mensa

The limit of magnitude for DSO's is approximately mag. 11.0. Regardless of magnitude all DSO's in the following catalogues and lists are included:

  • Messier
  • Lacaille
  • Dunlop
  • Bennett

The limit of magnitude for carbon stars is mag. 9.0.

Separate index files are included for Messier, Lacaille, Dunlop, Bennett, carbon stars, globular clusters and planetary nebulae.

8-10" Telescopes

The limit of magnitude for DSO's is approximately mag. 12.5. All of the objects in the 5-6" edition are included.
Regardless of magnitude all DSO's in the following lists and books are included:

  • Herschel 400
  • Herschel II
  • Burnham's Celestial Handbook
  • Caldwell

The limit of magnitude for carbon stars is mag. 9.5.

Separate index files are included for Messier, Lacaille, Dunlop, Bennett, Caldwell, Herschel 400, Herschel II, carbon stars, globular clusters and planetary nebulae.

12" Telescopes

The complete edition. The limit of magnitude for DSO's is approximately mag. 14.0. All of the objects in the 8-10" edition are included.
Regardless of magnitude all Herschel DSO's are included.

The limit of magnitude for carbon stars is mag. 11.0.

Separate index files are included for Messier, Lacaille, Dunlop, Bennett, Caldwell, Herschel, Herschel 400, Herschel II, carbon stars, globular clusters and planetary nebulae.

* The constellations of Dorado and Mensa contain a very large number of very small, extremely faint open clusters. Many will require a telescope aperture in excess of 12 inches to be observed.

Object Categories

The object categories in CSOG:

  • Carbon Stars - CS
  • Open Clusters - OC
  • Globular Clusters - GC
  • Nebulae - Neb
  • HII Regions - HII
  • Dark Nebulae - DN
  • Planetary Nebulae - PN
  • Supernova Remnants - SNR
  • Galaxies - Gx
  • Asterisms - Ast
  • Other - star clouds, quasars, double stars

CSOG was not written by simply compiling lists of objects only from well known catalogues, such as Messier, NGC and IC. That's the beaten track. CSOG's aim is to chart all of the DSO's and carbon stars that are truly within reach of small to moderately large amateur telescopes.

Catalog Editions

There a quite a few object catalogues and object lists that stargazers like to observe by. CSOG contains the following:

  • Messier
  • Lacaille
  • Dunlop
  • Herschel 400
  • Herschel II
  • Herschel
  • Hickson Compact Galaxy Groups
  • Arp Peculiar Galaxies
  • Holmberg Galaxies
  • Dolidze Open Clusters
  • Dolidze-Dzimselejsvili Open Clusters (they're actually all asterisms)
  • Stock Open Clusters
  • Palomar Globular Clusters
  • Terzan Globular Clusters
  • Caldwell
  • Bennett

Observing Programs

Observing guides for specific programs can be created from exisiting CSOG content. The following program is currently available. More to follow?

  • Astronomical Society of Southern Africa (ASSA) Top-100

Object Information

Along with an object's name its synonyms are included. Below the object's name and synonyms is its celestial coordinate in epoch J2000.0. To the right is relevant data such as magnitude and size. All data for non-galaxy DSO's was crosschecked with SIMBAD.

Where available a brief description is given. Instead of using the abbreviated Dreyer's descriptions, the description is always in complete words. Therefor you will not find a description such as "pL vF E gbM vbN" but will instead read "Pretty large, very faint, elongated and gradually brighter in the middle with a very bright nucleus".

A guide's title is the object category along with the name of its matching tourfile, using the constellation's abbreviation. For example, the second open cluster guide for the constellation of Cygnus is named "Cyg - OC-2". The tourfiles are named accordingly.

Field description

Along with the description of the object, a field description is included. It is a very useful feature. Noteworthy objects within 30 arcminutes (one degree centered on the object) and relatively bright stars that may aid in locating an object are included, along with bearing and distance: Stars up to mag. 10, double stars up to mag. 10 with a separation of 0.7 arcseconds or greater, carbon stars up to mag. 11 and of course all other carbon stars and DSO's in CSOG. Field descriptions always follow object descriptions and use a smaller font.


For every object there is a DSS image. Unless noted images are 30 by 30 arcminutes in size (30'×30', half a degree). Quite a few objects have larger images. A few very large objects have even larger DSS mosaics.
CSOG images are uncompressed. This is intentional as the option to zoom in on images is thereby retained. It is the reason the observing guides are quite large in size.

Image orientation

There are four options for image orientation:

  • Unmirrored: North up, east to the left
  • Mirrored horizontally - MH : North up, west to the left
  • Mirrored vertically - MV : South up, east to the left
  • Mirrored horizontally & vertically - MHV : South up, west to the left

If you are in doubt whether or not your telescope mirrors, observe a fixed object in daytime and compare the naked eye view to that in your eyepiece. Take care not to confuse the rotated image in a newtonian with a mirrored one.

There are no esthetically pleasing color images in CSOG. This is intentional. The guides are written to make the most of an observing session and are intended to primarily be used at night, behind the eyepiece of a telescope. The DSS images provide a standard reference.

Object sorting

Object mapObjects are sorted by constellation and by object category: Carbon stars, open clusters, globular clusters, nebulae, dark nebulae, planetary nebulae, supernova remnants, galaxies, asterisms and other. There are no more than three objects per page and generally no more than thirty objects per observing guide.
Objects are generally sorted by right ascension, or R.A. That means starting in the west and working towards the east, but not purely in R.A. When the next object is nearest in right ascension it may not be the closest as its declination may differ significantly from the preceding object, when another object may be much closer in declination but only slightly farther in right ascension. Therefor, CSOG objects are sorted to assure the distance between objects is minimized. Also, large constellations are divided into "blocks of declination". This allow for objects to be sorted logically in small part of a constellation, thereby minimizing large jumps in declination. This makes CSOG a very effective tool for "constellation sweeping".

Use of...

Clear Skies Observing Guides on an iPad

CSOG guides are best used on a tablet. Use of such a screen without additional measures will of course have an effect on your night vision. Therefor, tablets or computer screens must be dimmed as much as possible. In addition, a red screen cover, as dark as you can get it, should be used. It is up to you to decide which application to use to read the guides on your tablet.



Basic knowledge

To use the observing guides effectively some basic knowledge of the sky is required. It helps to be familiar with the celestial coordinate system (right ascension and declination) and units of measure (degrees°, minutes' and seconds"). Basically, you need to know how to read a starchart. Understanding directions in the eyepiece of your telescope (north, south, east, west) will aid in locating objects, finding object details and will help to locate objects in the vicinity such as the many double stars mentioned in the CSOG field descriptions. Knowing the actual field of view of your telescope-eyepiece combination will help to compare an object's DSS image to what you are observing and vice versa.

No starcharts

There are no CSOG specific starcharts. That does not mean CSOG is GOTO-telescope-only: Starcharts are not included because the starchart you already own will be all you need.
For all of the objects in the observing guides the celestial coordinates are included. This allows you to easily plot an object's exact location on your starchart, even when the object is not depicted on the chart. After you make the starhop and have the telescope pointed to the area where the object is, the DSS image will aid in locating the exact position.
If you insist on having a CSOG-specific finder chart to aid in locating an object, AstroPlanner is any easy way to create them. Planfiles containing all of the objects in the guides and tours are part of the CSOG concept and AstroPlanner allows for quick and easy creation of customized charts.

The potential for discovery...

Ever observed an object and noticed a faint smudge right next to it? I did. Did you heart skip a beat? Mine did. Ever worked out observations including a mystery object days, or even months after the observation... only to discover there is no object at that location? Been there, done that. And it happened only twice. In fact, it has been a major contributing factor to the creation of CSOG.

When using CSOG there will be no doubt whether or not there is an object in the vicinity. DSS images don't lie. If you ever stumble upon a faint fuzzy that really shouldn't be there, chances are that it's a mover. A mover that just might get your name attached to it. Why risk missing it?