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A new observational catalog from USNO is available

URAT is a follow-up project to the successful UCAC project using the same astrograph but with a much larger focal plane array.

Longer integration times and more sensitive, backside CCDs allowed for a substantial increase in limiting magnitude, resulting in about 4-fold increase in the average number of stars per square degree as compared to UCAC.

Additional observations with an objective grating largely extend the dynamic range to include observations of stars as bright as about 3rd magnitude. Multiple sky overlaps per year result in a significant improvement in positional precision as compared to UCAC.

M13 with URAT1 catalog

  • Observational catalog, i.e. mean positions of stars at mean epoch of URAT observing (between 2012.3 and 2014.6), on the International Celestial Reference System (ICRS).
  • Covering the about R = 3 to 18.5 magnitude range with positional precisions of 5 to 40 mas depending on observing history and brightness of stars.
  • Covering most of the northern hemisphere and in some areas as far south as -24.8 deg Dec (Pluto field).
  • Observed in a single bandpass (680 to 750 nm = between R and I).
  • Constructed from 2 years of operations of the astrograph at the Naval Observatory Flagstaff Station (NOFS), with multiple sky overlaps per year of regular exposures (240 sec and 60 sec) and objective grating exposures (30,20,10 sec)
  • Small systematic errors due to higher quality of the CCDs as compared to UCAC (expected error floor is about 5 to 10 mas)
  • URAT1 is supplemented by preliminary proper motions derived exclusively from 2-epoch URAT1 and Two Micron All Sky Survey (2MASS) data (at around epoch 2000) resulting in proper motion errors of typically 5 to 8 mas/yr.
  • Contains 228 million objects (mostly stars) of which 188 million are common to 2MASS
  • Photometry from 2MASS and American Association of Variable Star Observers Photometry All-Sky Survey (APASS) is added for stars in common

Read more details at

Access the catalog online from Vizier

You can show the URAT1 catalog data for a specific area in Skychart without downloading the full catalog by using the Virtual Observatory interface.

Start by zooming to a small sky area of the northern hemisphere, about 30 arcmin width, use preferably Equatorial coordinates.
Be sure the button “Show Virtual Observatory data” is checked.
Open the menu Setup → Catalog → VO Catalog, click the Add button.

Type URAT in the search field and click “By name” button, then “Select catalog”

Select “f.mag” for the magnitude, change Default magnitude to 19, click “Download catalog”

Be sure the new URAT line is green and click OK.

The chart now show the URAT1 stars for the selected area.
Save the program options to keep your VO catalog definition for a next time.

To show the stars for another area, open the menu Setup → Catalog → VO Catalog (or right click the “Show Virtual Observatory data” button).
Then click the reload arrow on the right column. When the download is finished click the OK button.

Build a local catalog for Skychart

Before to start check you have enough disk space available. There is about 17 GB of file to download, then it require 50 GB for the extracted data, and finally 5.8 GB for the Skychart catalog with only a minimal set of data without index.

Download the data, software and documentation from , for example:

mkdir URAT1
cd URAT1
wget --mirror
mv* .
cd ..

In the “access” directory compile the v1dump program. You need a Fortran compiler, for example gfortran, available in every Linux distribution or on Windows with Cygwin or Mingw.

cd URAT1/access
gfortran -o v1dump v1dump.f v1sub.f
cd ../..

For convenience for Windows users you can also download a precompiled v1dump.exe

Run v1dump to extract the data from the binary files to a new “asc” directory. Response to prompt are in bold.

cd URAT1
mkdir asc
cd access
dump URAT binary data to ASCII
hit "enter" to accept defaults or enter new values
path input = /d01/urat/v12/ 


binary data are stored in LINUX-style sequence
some computers (PC-style) need a byteflip
byte flip (Y/N) ?  N  


path output= ./                                      


first, last zone (326..900) to handle now =  326 327  

326 900

enter column separator character (default = blank) 
begin read file = ../v12/z326                                  
... output to   = ../asc/z326.asc   
... output to   = ../asc/z900.asc 

cd ..

Download the example project file for Skychart Catgen from

Then use Catgen to convert the text files to a binary catalog optimized for chart display.

cd URAT1
mkdir cat
ulimit -S -n 20000
Menu : Setup / Catalog / Catalog - Catgen, Load Project -> urat1.prj

If you use Linux or Mac OS, be sure to read the specific notes in the Catgen documentation page.

en/news/urat1_catalog.txt · Last modified: 2015/11/06 20:43 (external edit)