# Want even more stars ?

Making a map of any part of the sky with all the stars to magnitude 20 was only a dream for many years. Then a few solutions have emerged like USNO-A and USNO-B catalog. The old version of CdC can even get this data online for a limited area but the full USNO-B download was not available.

Now with the release of the much improved PPMXL catalog not only are the files available to everyone but the format allow you can process them immediately for use with CdC!

## PPMXL

The PPMXL catalog of positions and proper motions on the ICRS. Combining USNO-B1.0 and the two Micron All Sky Survey (2MASS).
Read more detail about this catalog: PDF.

Its advantage for mapping:

- Full sky coverage
- 900 million stars
- Complete down to magnitude 20
- Proper motions for every star
- Photometry from USNO-B and 2MASS

On the inconvenient side:

- Still some artifact near bright stars
- Many galaxies or parts of galaxy cataloged as stars

## Build a catalog for Skychart

The PPMXL files available for download at the CDS can be used without transformation by Catgen.

So the following sequence give you the catalog:

- Download the 720 files from the dat folder at ftp://cdsarc.u-strasbg.fr/pub/cats/I/317/ Beware this is about 38GB of files!
- Uncompress the .gz files (use gunzip on Linux or 7zip on Windows). The result take 148GB of disk space.
- Get the example Catgen project ppmxl.prj I use to build my version.
- Launch a recent version of Skychart and open Catgen
- Load the file ppmxl.prj , adjust all the file path and change the content option you want. Do not try to build a search index if you not have at least 24GB of RAM on your computer!
- Click the Build button and let your computer alone for some time, it take five hours on mine.
- At the end it eat 55GB more of your disk but you can now load the pxl.hdr file on the Catalog setting page and appreciate the result.

This is the only way you can get it, please don't ask me to put the files online for download! But it is easy to share with your friends on an external disk.