USNO A2.0 Stellar Data

The USNO A2.0 dataset is not recommended for astrometry due to the inaccuracy of the positions of the stars. Please use the more accurate UCAC2 or USNO B1.0 (subset) distributed with TheSky6.  See below.

Please refer to The Guide to Minor Body Astrometry <---- Click here for complete details

The following is a quote from the above link,

"It is the recommendation of the Minor Planet Center that observers who are still using the GSC as their reference catalogue should migrate to the USNO-B1.0, unless their field-of-view is large enough to contain sufficient UCAC 2 stars, in which case they should use the original form of this latter catalogue."

Although the above quote does not specifically address using the USNO A 2.0 stellar data for astrometry (only GSC) one can only assume the above holds true for the dated less accurate USNO A 2.0 data as well.

This document describes how to use the USNO A 2.0 stellar data with TheSky6.  If you have version 5 of TheSky click here for details.  However, it is strongly recommend that you upgrade TheSky version 5 to TheSky6. The astrometry performed in TheSky6 will be on the order of five times more accurate.

NOTE: There is no need to use the smaller single CD-ROM version of the USNO A2.0 data (54 million stars) with TheSky version 6. The newer stellar catalogs included with TheSky6, the UCAC2 and the USNO-B subset, are more accurate and recommended.

However, if you find there are not enough stars being plotted in TheSky6 (after verifying that you have a complete installation of TheSky6 Professional Edition using the UCAC2 and USNO-B subset) then consider using the 11 CD-ROM version of the USNO A 2.0 with 526 million stars (~1/2 a billion or better yet the complete USNO-B data with 1 billion stars). Remember if you choose to use the dated USNO A 2.0 stars for astrometry the astrometric solutions will not be as accurate as those using the UCAC2 or USNO-B1 data!

Warning, you must have administrative privileges when logged onto the machine in order to change the file locations.

Data | File Locations TheSky6

Use the "Verify All button"

Note that all valid databases will have a green check mark next to the name. If the UCAC2 and/or USNO-B1.0 Subset do not have a check mark they were not installed to the hard disk or the specified folder is incorrect.

If you have the USNO-B Full 80 gigabytes of 1 billion stars or you have the USNO A2.0 11 CD's make the changes here to tell TheSky6 where these datasets are located. Once the File Locations are correct, enable them here using View | Stellar Options.

View | Stellar Options | Catalogs/Astrometry

Enable those that apply!

To see the additional stars zoom into a field of view of less than 1 degree. This is done by design in an attempt to keep the field from being cluttered with too many stars.