USNO CCD Astrograph Catalog UCAC3

[citivolus]

My copy of UCAC3 arrived on Tuesday.

http://www.usno.navy.mil/USNO/astrometry/optical-IR-prod/ucac

Now to start working on getting it to work with my favourite software.

I should be able to redistribute the data to interested parties. It arrived on a double sided DVD, and I have yet to see the total file size.

The author of Cartes du Ciel has imported the data into a format that works with his software. That catalog is available here:

http://sourceforge.net/projects/skychart/files/2-catalogs/Stars/UCAC3/ (more info on his conversion here: http://www.ap-i.net/skychart/en/news/ucac3_catalog )

His version works out to just over 2GB including indexes.

Regards,
Eric

[Dennis]

Hi Ric

Some time ago I downloaded the USNO-A2.0 Catalog, which has some 526,280,881 stars. I think the download was over 6 GB – is this the same catalogue?

Cheers

Dennis

[citivolus]

UCAC3 is supposed to be less prone to error than the USNO-A2.0 catalog. It has a lower limiting magnitude (16), so in some cases the A2 data would still be useful.

The USNO-A2.0 data is known for its high photometric error. I'm not certain how it compares in that respect to UCAC3. Also, USNO-A2.0 does not have proper motions, and USNO-B1 has significantly higher estimated error in positional measurement than UCAC3.

USNO-B1 is still the largest & deepest data set, but rather hard to get your hands on if you need the whole database :)

One of the goals of UCAC3 was to be complete to magnitude 16, which is good for most of my usage. Beyond that you can still query USNO-B1 online for the region of interest.

Regards,
Eric

[Dennis]

Hi Ric

I’ve occasionally noticed that the plotted positions of the same star, when associated with difference reference designations, varies slightly when I toggle between the two designations in The Sky 6 Pro when zoomed in.

If I activate the UCAC label, the star appears in one position at a certain magnitude but if I then switch to the USNO A2.0 label, sometimes the star “moves” and the magnitude may also change, albeit very slightly.

Cheers

Dennis

[citivolus]

That sounds correct. Positions in UCAC3 are supposed to be in the range of 20-100 mas accuracy, while USNO A2/B1 positions are around 200 mas.

Note that I mentioned photometry earlier. My understanding is that UCAC3 isn't a good photometry source, as some imaging was done under light cirrus cloud. The primary goal was positional accuracy, so this will be a good database for, say, asteroid occultation prediction.

Regards,
Eric

[citivolus]

Here is a comparison of the two catalogs on the M8 and Omega Centauri regions. It shows how the USNO A2.0 catalog goes deeper, while the UCAC3 catalog includes stars in areas of nebulosity and closer to bright stars. Also, stars with high proper motions are indicated on the UCAC3 samples.

In the samples, UCAC3 is first, followed by the USNO-A2.0 for the same region.

[troypiggo]

Interesting. I must download this and see what I can see. Does it slow the performance of CdC at all?

I've wondered a few times about catalogues etc for CdC, comets, asteroids etc. Any other recommended ones?

[citivolus]

The Tycho 2 catalog is a good one for CdC.

Performance does not take that big of a hit, as you configure a given catalog to only be active above a given zoom level. This prevents it from selecting too many stars and overwhelming your system.

I have Tycho 2, UCAC3, and USNO-A2.0 all configured for use, as well as a custom catalog which contains the RCW objects. I can switch between them as needed by toggling them on and off via the configuration menu.

Regards,
Eric