C2A Add-in

C2a (Computer Aided Astronomy) is a wonderful free planetarium program developed by Philippe Deverchère in France. It has many great features and supports a whole lot of star catalogues including SAO, Guide Star, Hipparcos, Tycho-2 , USNO-SA1.0, USNO-A2.0, USNO-B1.0, UCAC1, UCAC2 and NOMAD (including NOMAD-Short).

I highly recommend this great piece of software to anyone that is interested in astronomy. I also totally recommend it for occultation observers because now C2A can draw occultations maps within a single click from OccultWatcher!

  1. --> Installing C2A

  2. --> How to use C2A to create occultation maps from within OccultWatcher

  3. --> How to get C2A to work with Hipparcos, Tycho2, UCAC2 and NOMAD

Installing C2A

Well to use this feature of OccultWatcher you will have to download and install the latest version of C2A from http://www.astrosurf.com/c2a/english/index.htm. It is about 12Mb in size. Then you will need some star catalogues and some of them are in C2As own format to speed up search. See below for more information.

How to use C2A to create occultation maps from within OccultWatcher

Before you can use the Add-in you will need to configure it. After you have installed C2A, go Add-ins -> Configure Add-ins -> C2A Add-in from the menu to open up the configuration screen

Then enter your desired field size and other options if desired. Press "Close" when done.

Now you are ready to go. There are two ways of creating the occultation map. First you can select the event and then go Add-ins -> Create C2A Occultation Map from the main menu or alternatively you can select the event and then use Create C2A Occultation Map from the context menu:

How easy was that! C2A will fire up and draw the occultation map. The target star will be in the center of the field. If you have configured any field markers such as CDD field rectangles they will be also shown.

Then when you print the star chart it will have information about the event such as asteroid, star, event time, star magnitude, magnitude drop, maximum duration and star altitude automatically included. You can add more to this or change it if you want from the Print Dialog in C2A

How to get C2A to work with Hipparcos, Tycho2, UCAC2 and NOMAD

These are the four catalogues used by Occult for asteroidal predictions and therefore predictions involving stars from any of them can be shown in OccultWatcher. Because of that you will probably want to have these four catalogues setup in C2A and the following information could help you with that.

Hipparcos is a small catalogue and you can download Hipparcos.zip from C2A's web site. The zip file is 6.5Mb and the catalogue is in it's own format so you will need to download it even if you already have another distribution of this catalogue.

Tycho-2 is not small at all but I would recommend you to download Tycho-2.zip from C2A's web site (~150Mb). Again C2A requires the catalogue to be in its own format so if you have another distribution of Tycho-2 already it will not work.

You should store the Hipparcos and Tycho-2 catalogs in a separate folder (e.g. C:\Catalogues) and configure the paths in C2A later on (see below).

UCAC2 is again a different story. The catalogue is about 2Gb and the best way to get it is from your local astronomy club or a fellow astronomer. Alternatively if you have a very fast internet connection and a big quota you can download the 1.6Gb files from http://badc.lamost.org/archives/UCAC2/bindat/ or from http://vizier.hia.nrc.ca/viz-bin/ftp-index?/ftp/cats/bincats/UCAC2/bindat/. You will then have to reconstruct the catalog using the makeucac.zip utility. Full details about reconstructing UCAC2 can be found here. When done you should have files z001 to z288. If you have files z001.bin to z288.bin then you'll need to reconstruct the catalog before going further.

The UCAC2 catalogue that you have downloaded needs to be compiled in a format which is specific to C2A in order to accelerate the display of the maps. Once you have all the "z" files from z001 to z288 you will also need to download the supplementary files s01 to s36 (BSS.zip ~14Mb) from C2A's web site. Then place all the files in the same folder and download the UCAC2 Compiler and extract UCAC2.EXE in the same location. Make sure you have at least 6Gb free disk space on the same drive.

You will have to run UCAC2.EXE to "compile" UCAC2 in C2A's format. To do this run a command prompt by going Start -> Run, type "cmd" and press enter. Then make sure you are in the correct folder (you may have to use "cd" to change the directory e.g. (1) C:\>d: and then (2) D:\cd Catalogs\UCAC2). Finally type "ucac2 ." and press enter.

The operation may continue 60 minutes or more depending on your computer speed and configuration. On Pentium III on 1GHz it takes 2 hours 30 min so be patient. In the end you will get files (UCAC2_00.DAT to UCAC2_23.DAT) created in the same location.

NOMAD is the biggest catalogue and goes down to magnitude 20. It's full version can be only distributed on a hard drive simply because storing 100Gb on DVDs will be impractical and a download of this size would be difficult. The predictions in OccultWatcher which may involve stars that are only listed in NOMAD should be brighter than magnitude 16 so you actually don't need the full version of NOMAD. A shorter version of the catalogue called NOMAD-Short was created by Dave Herald for the use with Occult and this is the version used for predictions published in OccultWatcher. NOMAD-Short fits on a single DVD and the best way to get it is to ask your local astronomy club. You can also ask for a copy in IOTAOccultations or RASNZOccultations mailing list if you live in US, Australia or New Zealand. People in Europe should ask in the PLANOCCULT mailing group. For the other parts of the world you should ask in IOTAOccultations.

The good news about NOMAD is that C2A can use NOMAD (and NOMAD-Short) without the need to compile them (as it does with UCAC2).

Finally you need to configure the paths to the catalogues in C2A so they can be used. To do this you should go Tools -> Options or press F7, then switch to the "Paths" tab and configure the paths for the Hipparcos, Tycho-2, UCAC2 and NOMAD catalogues."

For any additional information you can check the C2A Web Site or you can post your questions in the Occult Watcher Yahoo Group