C2A lets you define your own catalogues of objects as text files. The command User catalogues ... in the File menu allows you to load catalogues and to display them in the field map. Note that C2A also allows you to compile your own catalogues of objects (see the section: How to compile user catalogues of objects).
Users can define their own objects to be displayed in the same way as those in databases supplied with the program.
User objects defined in textual databases are represented by the same symbols as deep sky objects or solar system objects (asteroids, comets, etc…). Have a look at the object symbols section to see the symbols associated with different kinds of objects.
User objects which have an apparent size on the celestial sphere are displayed with circles or ellipses which reflect this size.
You can put a string of characters (maximum 32) at the beginning of the user file to succinctly describe its content. This optional string must be on the first line of the file and begin with the “$” character. When you load this database file, C2A will use this description to identify it (in addition to the file name).
Example: $ Uppsala General Catalogue
For a file to be automatically recognised as a user text file, it must have the extension “c2a”. Without this convention, user files will not be automatically recognised in the database directory specified through the User catalogues… command in the File menu.
For stars, the declarations must have the following form:
star, <right ascension>, <declination>, <magnitude>, <spectral type>, [<name>], [<comment>];
For galaxies, declarations must have the following form (see the following table for an understanding of the detailed syntax in each field):
galaxy, <right ascension>, <declination>, <magnitude>, [<ellipse>], [<name>], [<comment>];
For all extended objects which can have two different dimensions (and can therefore be represented by an ellipse), which is to say, open clusters, diffuse nebulae, dark nebulae, planetary nebulae, galaxy clusters and un-classified user objects, declarations must have the following form:
<type1>, <right ascension>, <declination>, [<magnitude>], [<ellipse>], [<name>], [<comment>];
For all extended objects having only one dimension (and can therefore be represented by a circle), i.e. globular clusters, supernovae, pulsars and quasars, the declarations must have the following form:
<type2>, <right ascension>, <declination>, [<magnitude>], [<size>], [<name>], [<comment>];
Finally, declarations for other dimensionless objects, that is, simple stars, double stars, multiple stars, asteroids, comets and satellites, have the following syntax:
<type3>, <right ascension>, <declination>, [<magnitude>], [<name>], [<comment>];
Note: The characters [ and ] denote an optional field. Note also that if an optional field is included in the declaration of an object, all the optional fields of preceding this one must also be included (for obvious reasons of interpretation).
The syntax of different fields is described below:
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<type1> |
This is the type of declared object (with two possible dimensions) and the keyword should be one of the following:
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<type2> |
This is the type of declared object (with one possible dimension) and the keyword should be one of the following:
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<type3> |
This is the type of declared object (without dimensions) and the keyword should be one of the following:
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<right ascension> |
Right ascension of the object for the equinox 2000. This declaration must have the form AhBmCs where A and B are integers and C a real number. The characters h, m and s are optional and may be replaced by spaces. You can also use the form AhBm if you do not want to specify seconds of time. |
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<declination> |
Declination of the object for the equinox 2000. This declaration must have the form A°B'C'' where A and B are integers and C a real number. The characters °, ' and '' are optional and may be replaced by spaces. You can also use the form A°B' if you do not want to specify arc seconds. |
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<magnitude> |
Magnitude of the object (as a real number). |
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<spectral type> |
Spectral type of the star. This must be a letter from the list: O, B, A, F, G, K, M, C. |
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<ellipse> |
The field allows you to define the major and minor axes and the inclination of a galaxy (or another two-dimensional object) which can be represented by an ellipse. It comprises three real numbers separated by spaces: <major axis> <minor axis> <inclination> The major and minor axes must be expressed in arc minutes and the inclination is calculated from the North towards the East in degrees (which must be between 0 and 360°). If the major and minor axes have a value of 0, the object will be represented by a symbol and not an ellipse or a circle. If the minor axis is 0, the object will be represented by a circle. Additionally, if the inclination is -1, C2A will assume the latter is unknown and will display an ellipse of zero inclination and a specific colour (which tells the user that the inclination is unknown). An example of a declaration is given later in this section. |
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<size> |
This field lets you define the size in arc minutes of an extended object represented by a circle. This is therefor used for objects of the type: globular clusters, supernovae, pulsars ans quasars. If you do not want to specify a size (because, for example, you don’t know it) just use the value 0. User objects which have a declared size will be displayed with a dotted cicle (above a certain level of zoom) whose radius corresponds to the declared size. |
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<name> |
Optional name of the object. This must be a character string within quotation marks and may include spaces. Example: “delta Orion”. When launching a Search by name…, C2A uses this field, if it is present, to search objects in user catalogues. |
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<comment> |
Optional comment attached to an object. As with the field <name>, the comment must be a string of characters between quotation marks and may include spaces. Example: “The most beautiful nebula in the heavens”. At this stage, C2A does not use this field. |
A declaration must be contained in a single line (even if it has more than 80 characters).
The character ‘#’ indicates the presence of a comment at the end of as line (the comment will be ignored by the program).
It is possible to associate a block of several lines of comment with an object (not to be confused with the field <comment> placed at the end of the declaration). To do this, just place before the declaration of the object a block of text enclosed by “%” at the beginning of a line. There is no limit to the number of lines in a comment block. The following example illustrates the use of a comment block.
Example:
%
Example of a
comment block associated with the following object. In this example, the galaxy
will be represented by a 6.5’ par 2.7’ellipse with an inclination of 135° with
respect to North
%
galaxy, 0 3 15, 16 8 42, 12.0, 6.5 2.7 135, "UGC 8"
Note that to find a user object, just type its name in the rapid search area of the find object box and OK it with the ENTER key. The object can only be found if the user catalogue is active in the dialogue box which lets you manage user catalogues.