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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.

Object Information

NGC4725 in the constellation of Coma Berenices - an example of a galaxy in CSOG Carbon star TW Horologii, with its neigbour (in the background) galaxy PGC11984 Galaxy PGC11984 in Horologium, with its neighbour (in the foreground) the carbon star TW Horologii

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. Read more about the CSOG objects and the catalogues and lists the guides contain on the Objects page.
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 "Open Clusters (Cyg - OC-2)". The tourfiles are named accordingly.

Field descriptions

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.

An early summer observing run using Clear Skies Observing Guides.Clear Skies Observing Guides on an iPad, dimmed and red foil applied: The future of observing is here. Clear Skies Observing Guides on an iPad, dimmed and red foil applied: The future of observing is here.


For every object there is a DSS image. The majority of the images are 30 by 30 arcminutes in size (30'×30', half a degree). Larger objects have larger images, either 45, 60 or 75 arcminutes in size. 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.

CSOG Image orientation options

There are four options for image orientation to best suit your planning or observing needs:

  • True - 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.

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 for all objects.

Object sorting

Object mapThe guides 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".

Constellation Editions

North & South North only South only
Antlia Leo Andromeda Apus
Aquarius Lepus Auriga Ara
Aquila Libra Camelopardalis Carina
Aries Lupus Canes Venatici Chameleon
Boötes Microscopium Cassiopeia Circinus
Caelum Monoceros Cepheus Crux
Cancer Ophiuchus Corona Borealis Dorado
Canis Major Orion Cygnus Grus
Canis Minor Pegasus Draco Horologium
Capricornus Pisces Lacerta Hydrus
Centaurus Piscis Austrinus Leo Minor Indus
Cetus Puppis Lynx Mensa
Columba Pyxis Lyra Musca
Coma Berenices Sculptor Perseus Norma
Corona Australis Scorpius Triangulum Octans
Corvus Scutum Ursa Major Pavo
Crater Serpens Ursa Minor Phoenix
Delphinus Sextans   Pictor
Equuleus Sagitta   Reticulum
Eridanus Sagittarius   Telescopium
Fornax Taurus   Triangulum Australe
Gemini Virgo   Tucana
Hercules Vulpecula   Vela
Hydra     Volans

CSOG covers all of the 88 constellations. Along with the complete work covering all of the sky there are northern and southern hemisphere editions. Of course, there is considerable overlap between the two hemispheres.

The constellation of Serpens is divided into separate guides for Serpens Caput and Serpens Cauda. No constellations are divided into separate northern or southern hemisphere parts.

CSOG Constellation editions are available in three telescope aperture classes:

  • 5-6" telescopes
  • 8-10" telescopes
  • 12" and larger telescopes - the complete edition

The above aperture division is a rule of thumb. Every edition contains the objects that will allow you to get the most out of your equipment. That may require very good conditions: Dark skies and great transparency. That being said, (sub)urban observers using a 8" telescope will enjoy observing the objects in the 5-6" version as it contains brighter objects than the 8-10" edition does. Then again, if you have access to a truly dark sky site, you may want to hunt down all the faint fuzzies in the 12" guides.

Read more about the objects per telescope aperture on the Objects page.


Catalog & Object Editions

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

  • Messier, sequentially, by constellation or sorted for a Messier marathon
  • Lacaille, sequentially or by constellation
  • Dunlop, by constellation
  • Herschel, by constellation and object category
  • Herschel 400, by constellation
  • Herschel II, by constellation
  • Caldwell, sequentially or by constellation
  • Bennett, sequentially or by constellation
  • Palomar Globular Clusters, sequentially or by constellation
  • Terzan Globular Clusters, sequentially or by constellation
  • Hickson Compact Galaxy Groups
  • Carbon Stars, by constellation, All Sky or by hemisphere and by telescope aperture: 5-6", 8-10" or 12"
  • Globular Clusters, by constellation, All Sky or northern hemisphere and by telescope aperture: 5-6", 8-10" or 12"
  • Planetary Nebulae, by constellation, All Sky or by hemisphere and by telescope aperture: 5-6", 8-10" or 12"

More about the objects in the list and catalogues on the Objects page.

Use of...

Clear Skies Observing Guides on an iPad Clear Skies Observing Guides on an iPad with red PVC cover

CSOG guides are best used on a tablet. Use of such a 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 a tablet.
For iPad users the app Filebrowser is recommended to store and organize observing guides. A great reading app is PerfectReader Pro, as it allows documents to be dimmed much farther than is possible in other apps and fills out documents to the edge of the screen.



Basic knowledge

To use the observing guides effectively some basic knowledge of the sky is an advantage. It helps to be familiar with the celestial coordinate system (right ascension and declination) and units of measure (degrees°, minutes' and seconds"). Knowing 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 actually 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?