The C2A help system is finally available in English! This has been made possible thanks to John Beavis who has been brave enough to translate the almost 100,000 words of the help system, checking step by step the alignment of the help text with the program interface. Words cannot express C2A author's gratitude to John for this enormous task. It took John less than 5 months to patiently, meticulously, complete the task and the quality of the translation is truly impressive. John's professional background is in Archaeological Sciences, but there is no doubt he also has high skills in astronomy and... French!

What is C2A ?

C2A is a planetarium software which allows you to access the SAO star catalogue, the Guide Star catalogue, the Hipparcos and Tycho-2 catalogues, the GCVS, WDS and Gliese catalogues as well as the UCAC1, UCAC2, UCAC3, UCAC4, NOMAD, PPMXL, CMC15 and URAT1 catalogues. C2A also integrates 6600 objects (contained in 4649 images) from the Buil-Thouvenot Atlas (BT-Atlas). Thanks to C2A you may display all the images in the BT-Atlas in their full dynamic range (images are 16bit, 65536 grey levels). C2A incorporates the Revised New General Catalogue and Index Catalogue (with their associated historical attributes) and a deep sky catalogue (RNGC and NGC2000), both complementary catalogues of the BT-Atlas. C2A is released with the Saguaro Astronomy Club deep sky object catalogue. The Catalog of Principal Galaxies (PGC 2003) is also provided in the standard distribution of C2A (this catalogue is more than 38 MB once decompressed). C2A permits you to access images from the Digitized Sky Survey of ESO or STScI and display these either in a separate window or in the background of the current field. C2A natively integrates the Loneos catalogue (UBVRI photometry of faint field stars). C2A allows you to define your own object catalogues using a well specified textual syntax, and it is also able automatically and at regular intervals to download the Be star catalogue ArasBeAM, Meteor Shower and the Exoplanet transit database from the Internet. Finally, C2A includes an Asterism catalogue derived from several catalogues available on the Internet.

Beyond its capacity to visualize numerous star and deep sky object catalogs, C2A integrates several useful tools in order to prepare and execute observation sessions: an observation logbook, an observation planner tool, an observation scheduler tool, a tool to plot mount tracking drifts, a polar clock utility, a module to control telescopes, a powerful image processing tool with specific capabilities around image acquisition, polar alignment with the King method and astrometric analysis, a module to analyze image quality, a tool to plot asteroid and comet positions, a module to plot solar system object positions, an ephemeris production tool, a table of the Moon phases, a tool to display the sunrise, sunset and twilight times, a module to display planet position and visibility, a tool to get a global view of the ecliptic and a tool to display object visibility.

The Help System

The help system provides information about how to use C2A. The most common actions are described as well as explanations on each of the main application dialog boxes. Alternatively, you can obtain information about the elements of dialog boxes through a system of help bubbles: when you are in a dialog box, leave the immobile mouse over an element during a second and a small help bubble will appear near the cursor.

Anytime, you can press the F1 key to get help about the current window or dialog box.

How do you use C2A ?

All software interactions occur through 4 zones of the main screen (menu, toolbars, display area of the field and dialog box). Typical tasks using C2A are as follows:

Use the Help Contents button from the Help window to access the different sections of the help system. This help system also has a summary of keyboard shortcuts to facilitate your use of C2A.

Characteristics of C2A


C2A was designed to meet the following objectives:


-        It must be easy to use, and it should not be necessary to read a manual to master it.

-        It must take into account major catalogues which are currently available (Guide Star, USNO-SA1.0, USNO-A2.0, USNO-B1.0, UCAC1, UCAC2, UCAC3, UCAC4, NOMAD, PPMXL, CMC15, URAT1, Hipparcos, Tycho-2, GCVS, WDS, Gliese) as well as additional information on the brightest stars (SAO). For the catalogues Tycho-2, Hipparcos, WDS, UCAC1, UCAC2, UCAC3, UCAC4 and URAT1, proper motions are taken into account in calculating coordinates of objects based on the date of observation, thus with the objective to perform astrometry and photometry.

-        It must be able to display images from the BT-Atlas with their full dynamic range (64000 colours). This function could be used to search for supernovae in galaxies.

-        It must permit access to images from different “surveys” in the Digitized Sky Survey.

-        It must include a utility that uses orbital elements to compute trajectories of asteroids and comets (with direct access to the internet). This tool is very useful in undertaking research into asteroids.

-        It must provide high accuracy for the calculation of planetary positions in astrometric coordinates (and not apparent coordinates), which is necessary to compare the position of the objects in the solar system with the background of stars. This ability is useful when observing occultations.

-        It must include a complete ephemeris generator including known asteroids and comets from their orbital elements.

Updates and support

C2A software updates can be downloaded from the website :

This site also contains information about using C2A as well as updates for comets and asteroids orbital element files.

Support and additional information may also be obtained by sending an e-mail to the following address:

Help system version:

C2A Help System - Version 4.4 release 1, October 16, 2016.

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