Overview of UCAC project
The US Naval Observatory Twin Astrograph is used with a 4k CCD
for direct imaging of the sky with guided exposures. A single
frame covers just over 1 square degree. The astrometric catalog
is constructed using Tycho reference stars.
As part of the project, extragalactic radio reference sources
are observed with bigger telescopes and the corresponding fields
are observed simultaneously with long exposures at the astrograph.
The final UCAC catalog will have the option to tie in
directly either to the fainter half of the Hipparcos stars
or to some 500 extragalactic sources as an alternative
reference frame to the Tycho stars.
The following table gives details about the data acquisition.
------------------------------------------------------
number of exposures 2 per field
exposure times 25 & 125 seconds, guided
observing throughput 13 fields/hour
overlap pattern 2 fold
number of fields 85,158 all sky
sky coverage complete by mid 2004
sky coverage 95% complete, September 2003
southern hemisphere location: CTIO, Chile
northern hemisphere location: Flagstaff, Arizona
------------------------------------------------------
average density 1800 stars / square degree
total 35 million stars / hemisphere
catalog accuracy 20 mas R = 10 to 14 mag
30..40 mas R = 9 mag, 15 mag
70 mas R = 16 mag = limit
------------------------------------------------------
The following table gives details about the amount of data
acquired until 2003 October 22.
---------------------------------------------------------------
project time so far 5.7 years 1998 Feb - 2003 October
total number of frames 257,000 including rejects
raw data 4.1 TB compressed FITS
backup on > 1100 exabyte tapes (single copy)
> 6000 CD--ROMs (single copy)
detection output 200 bytes/object
number of stars > 60 million (with at least 2 images)
------------------------------------------------------