Quote Originally Posted by datscope View Post
HI Bob
I do get pointing issues in different parts of the sky. Some areas are great no issues, others have problems. Maybe it isthe catalouge?
Hi Dave,

Well, yes and no, it is the catalog and isn't. The catalog reflects the distribution and numbers of stars per square degree in the sky. The distribution of stars at a given magnitude across the sky is not uniform. You'll see many more stars in the directions along the Milky Way, and fewer stars in directions perpendicular to the galactic plane (away from the plane of the Milky Way). So the catalog mimics the way the stars are actually distributed in the sky. This will, therefore, create problems for guiding or for plate solving, all depending on where you're looking, as in the sparser areas of the sky.

The GSC goes down, maybe, to 12th magnitude. The USNO A2.0 catalog goes down to 19th, which is why it's a significantly larger catalog file than the GSC.

If you open the ACP Reference Guide (http://solo.dc3.com/ar/ACPRefGuide.html) and click on "Star Catalog Information," at the bottom of that screen is a link called: "Where can I get a copy of the <...> catalog?" and therein is a paragraph and link to the UNSO A2.0 catalog page. Here's the URL directly: ftp://ftp.nofs.navy.mil/usnoa/

This is a huge catalog (6,000 megabytes) but you can download it via ftp in bits and pieces at night if needed. Not recommended for dialup lines! Copy the readxxx.xxx files and the zonexxxx.acc and zonexxxx.cat files in this directory to a directory/folder on your system. All A2.0 files must be accessible and in one folder. In ACP, set your catalog type to USNO A2.0. Set your catalog path to the directory into which you copied the files from USNO. They will all be in one folder.

The USNO B1.0 is an even more huge catalog, only really accessible online. ACP can use it, but it means there will be a wait for an Interent connection, query, and data return online for each and every plate solve that's done. If that's infrequently in your case, it may be a good alternative. The USNO A2.0 is still an active and useful catalog to have on your computer.