About
C2A (Computer Aided Astronomy) is a free, feature-rich stellar cartography and planetarium software exclusively for Microsoft Windows. Designed for amateur astronomers, researchers, and educators, it enables the preparation of detailed observations of small celestial fields and supports astrometric and photometric work. The software integrates an extensive range of star catalogs, including SAO, GCVS, WDS, Gliese, Hipparcos, Tycho-2, USNO-A/B series, UCAC1–4, NOMAD, PPMXL, CMC15, URAT1, and GAIA. For deep-sky objects, it bundles the Revised NGC/IC, PGC 2003, SAC 8.1, and BT-Atlas (6,600 objects with 4,649 images). Photometry is natively supported via the Loneos UBVRI catalog. C2A connects to the internet to access live catalogs such as ArasBeAM (Be-star spectroscopy), the Exoplanet Transit Database, and the UAI Meteor Showers list. It can retrieve digitized sky survey images from ESO DSS and STScI DSS servers, display asteroid and comet trajectories, compute planetary ephemerides, and show artificial satellite positions via TLE orbital elements. Additional highlights include telescope control integration, an asterism catalog, support for custom user-defined object catalogs (text or compiled), and BT-Atlas image overlays. C2A is entirely free for non-commercial use, certified clean by Softpedia, and is widely recognized as one of the best free planetarium applications available.
Key Features
- Comprehensive Star Catalog Support: Integrates over 15 major star catalogs including Hipparcos, Tycho-2, USNO series, UCAC1–4, NOMAD, and GAIA for highly detailed stellar field views.
- Deep-Sky Object Libraries: Bundles NGC/IC, PGC 2003, SAC 8.1, and the BT-Atlas with 6,600 deep-sky objects and 4,649 associated images for rich observing sessions.
- Astrometry & Photometry Tools: Supports astrometric measurements and photometric analysis with native integration of the Loneos UBVRI catalog for faint field stars.
- Telescope Control & Tracking: Controls telescopes directly from the software, and can display asteroid/comet trajectories, satellite positions via TLE elements, and compute ephemerides.
- Live Internet Catalog Access & DSS Imagery: Fetches real-time data from ArasBeAM, the Exoplanet Transit Database, and UAI Meteor Showers, plus digitized sky survey images from ESO DSS and STScI.
Use Cases
- Planning and preparing detailed observations of small stellar fields before a night session.
- Performing astrometric measurements and photometric analysis of variable stars or field stars.
- Tracking exoplanet transits using integrated Exoplanet Transit Database access.
- Monitoring and displaying artificial satellite positions using TLE orbital element data.
- Exploring deep-sky objects with bundled NGC/IC and BT-Atlas image overlays for visual or imaging sessions.
Pros
- Completely Free: C2A is freeware for non-commercial use, certified clean by Softpedia, with no subscription or hidden costs.
- Extensive Catalog Coverage: Access to more than 15 major star and deep-sky catalogs—bundled or downloadable—gives serious observers unmatched data depth.
- All-in-One Astronomy Suite: Combines planetarium viewing, astrometry, photometry, telescope control, satellite tracking, and ephemeris calculation in a single application.
Cons
- Windows Only: C2A is exclusively available for Microsoft Windows, with no support for macOS, Linux, or mobile platforms.
- Development Pace Dependent on Author's Free Time: As a solo passion project, new features and bug fixes are not guaranteed on any schedule, which may limit timely updates.
- French-Centric Documentation: Primary documentation and the website are in French, which can be a barrier for non-French-speaking users.
Frequently Asked Questions
Is C2A free to use?
Yes, C2A is entirely free for non-commercial use. Donations are welcomed to support the developer but are not required.
What operating systems does C2A support?
C2A is available exclusively for Microsoft Windows (all versions). There is no Mac, Linux, or mobile version.
Which star catalogs come bundled with C2A?
The installation includes SAO, GCVS, WDS, Gliese, and Hipparcos catalogs. Additional large catalogs like Tycho-2, USNO, UCAC, and GAIA can be downloaded separately.
Can C2A control my telescope?
Yes, C2A includes telescope control functionality, allowing you to point and operate compatible telescopes directly from the software.
Does C2A require an internet connection?
Not for core functionality. However, an internet connection is needed to access live catalogs (ArasBeAM, Exoplanet Transit Database, meteor showers) and to retrieve DSS sky survey images.
