The 3rd Release of the Sloan Digital Sky Survey Moving Object Catalog


The 3rd Release of the Sloan Digital Sky Survey Moving Object Catalog lists astrometric and photometric data for 204,305 moving objects observed prior to June 2004. Of those, 67,637 are linked to 43,424 unique objects from ASTORB file, and their orbital elements are also listed. This is a cumulative release, and it supersedes the first and the second releases.


The purpose of this catalog (the Sloan Digital Sky Survey Moving Object Catalog, hereafter SDSSMOC) is to promptly distribute data for moving objects detected by SDSS. While some of these data have already been released as a part of regular SDSS Data Releases , it may be more convenient for many users to have the relevant data in a simple text file. In addition, the proposed selection cuts have been tested in practice, and corresponding estimates of the sample completeness and contamination are available (see below). Of course, you can design your own selection criteria and start from scratch.

The first release of SDSSMOC included all data obtained up to Dec 15, 2001. The catalog includes data for 58,117 moving objects from 87 observing runs that roughly cover the area included in the SDSS Data Release 1 (January 1, 2003).

The second release of SDSSMOC includes 134,335 moving objects from 194 observing runs obtained up to March 11, 2003. Objects from the first release are included in the second release because the photometric pipeline and flatfield vectors changed a bit between the two releases.

This third release of SDSSMOC includes 204,305 moving objects from 301 observing runs obtained up to June 2004. Objects from the first two releases are included because the photometric pipeline and flatfield vectors (again) changed. Due to changes in photometric pipeline, for the same runs that are included in both the first and the third release, ~7% of objects from the first release are NOT included in the third release, while there are ~15% more objects in the third release. As a result of these changes, the sample completeness and contamination in the third release are estimated to be ~95% and ~6%, respectively (estimated with an accuracy of 1-2%). These values are somewhat different than ~90% and ~3%, respectively, that were reported by Ivezic et al. (2001): the sample completeness slightly increased, with a corresponding increase of sample contamination.

SDSSMOC will be updated about once for every major SDSS Data Release. We plan several additional releases before the end of the survey.

The catalogs includes various identification parameters, SDSS astrometric measurements (position and velocity, with errors), SDSS photometric measurements (five SDSS magnitudes and their errors), and orbital information for previously cataloged asteroids.

Data Selection

For methods of accessing SDSS data products, and detailed product description, please see SDSS EDR paper (Stoughton et al. 2002, Astronomical Journal, 123, 485). The moving object catalog contains all the objects from included runs that satisfy the following query:
   (objc_type == 6) 
   (psfCounts[2] > 14.5) && (psfCounts[2] < 21.5) 
   (rowv*rowv + colv*colv > 0.0025)
   (rowv*rowv + colv*colv < 0.25)
The first line excludes all saturated and "bright" objects (the latter are always duplicates of physical objects produced by processing software), and the second line requires that the object was recognized as a moving object by SDSS photometric pipeline (Lupton et al. 2005, in prep; see also a paper about SDSS moving objects by Ivezic et al. 2001, hereafter Paper I). The third and fourth lines require that the object is unresolved and brighter than r=21.5, and the last two conditions require that the magnitude of the object's velocity vector is larger than 0.05 deg/day and smaller than 0.5 deg/day. Note that some of these entries are multiple observations of the same objects (see Section 3.3. in Paper I).

The completeness (number of moving objects detected by the software that are included in the catalog, divided by the total number of moving objects recorded in the images, for details see Juric et al. 2001, hereafter Paper II) of the third release catalog is about 95%, and its contamination rate is about 6% (the number of entries that are not moving objects, but rather instrumental artifacts, for details see Paper I). That is, in the third release catalog (ADR3.dat, see below) about 10,000 observed moving objects were missed by the processing software, and about 12,000 catalog entries are instrumental and software artifacts.

Post Processing

We matched 204,305 moving objects from ADR3.dat to known objects listed in the ASTORB file (see Paper II), and found 67,637 matches (for 43,424 unique objects). The osculating orbital elements from ASTORB file for these objects are also listed in the catalog, as well as proper orbital elements computed by Milani et al. (1999, Icarus, 137, 269), when available.

Using these supplemental orbital data, the SDSS colors can be used to produce informative plots of asteroid distribution in orbital parameter space; e.g. see a "colorful" plot of asteroid distribution in the proper inclination vs. semi-major axis plane. Details about this plot can be found in Ivezic et al. 2002, Paper III (pdf).

The Catalog Format

The catalog is distributed as uncompressed ASCII file (132 MB), and a gzip compressed file (27 MB), with one record (line) per object observation (see below for file links). Each record contains:

Field Columns
[start, end)
Field Description
-- SDSS identification --
1 1 - 7 moID Unique SDSS moving-object ID
2 8 - 13 Run SDSS object IDs, for details see SDSS EDR paper
3 14 - 15 Col
4 16 - 20 Field
5 21 - 26 Object
6 27 - 35 rowc Pixel row
7 36 - 44 colc Pixel col
-- Astrometry --
8 47 - 59 Time (MJD) Modified Julian Day for the mean observation time
9 60 - 70 R.A. J2000 right ascension of the object at the time of the (r band) SDSS observation
10 71 - 81 Dec J2000 declination of the object at the time of the (r band) SDSS observation
11 82 - 92 Lambda Ecliptic longitude at the time of observation
12 93 - 103 Beta Ecliptic latitude at the time of observation
13 104 - 115 Phi Distance from the opposition at the time of observation
14 117 - 124 vMu The velocity component parallel to the SDSS scanning direction, and its error (deg/day)
15 125 - 131 vMu Error
16 132 - 139 vNu The velocity component perpendicular to the SDSS scanning direction, and its error (deg/day)
17 140 - 146 vNu Error
18 147 - 154
The velocity component parallel to the Ecliptic (deg/day)
19 155 - 162
The velocity component perpendicular to the Ecliptic (deg/day)
-- Photometry --
20 164 - 169 u SDSS u'g'r'i'z' psf magnitudes and corresponding errors
21 170 - 174 uErr
22 175 - 180 g
23 181 - 185 gErr
24 186 - 191 r
25 192 - 196 rErr
26 197 - 202 i
27 203 - 207 iErr
28 208 - 213 z
29 214 - 218 zErr
30 219 - 224 a a* color = 0.89 (g - r) + 0.45 (r - i) - 0.57 (see Paper I)
31 225 - 229 aErr
32 231 - 236 V Johnson-V band magnitude, synthetized from SDSS magnitudes
33 237 - 242 B Johnson-B band magnitude, synthetized from SDSS magnitudes
-- Identification --
34 243 - 244 Identification flag Has this moving object been linked to a known asteroid (0/1)? See Paper II.
35 245 - 250 Numeration Numeration of the asteroid. If the asteroid is not numbered, or this moving object has not yet been linked to a known asteroid, it's 0.
36 251 - 271 Designation Asteroid designation or name. If this moving object has not yet been linked to a known asteroid, it's '-'
37 272 - 274
Detection Counter
Detection counter of this object in SDSS data
38 275 - 277 Total Detection Count Total number of SDSS observations of this asteroid
39 278 - 286 Flags Flags that encode SDSSMOC processing information (internal)
-- Matching information --
40 288 - 298 Computed R.A. Predicted position and magnitude at the time of SDSS observation for an associated known object computed using ASTORB data
41 299 - 309 Computed Dec
42 310 - 315 Computed App. Mag.
43 317 - 324 R Heliocentric distance at the time of observation
44 318 - 325 Geocentric Geocentric distance at the time of observation
45 333 - 338 Phase Phase angle at the time of observation
-- Osculating elements --
46 340 - 350 Catalog ID Identification of the catalog from which the osculating elements and (H, G) values were extracted
47 361 - 366 H Absolute magnitude and slope parameter
48 367 - 371 G
49 372 - 377 Arc Arc of observations used to derive the elements
50 378 - 391 Epoch Osculating elements
51 392 - 404 a
52 405 - 415 e
53 416 - 426 i
54 427 - 437 Lon. of asc. node
55 438 - 448 Arg. of perihelion
56 449 - 459 M
-- Proper elements --
57 461 - 481 Proper elements catalog ID Identification of the catalog from which the proper elements were extracted
58 482 - 494 a' Proper elements
59 495 - 505 e'
60 506 - 516 sin(i')
61-124 517 - 644 binary processing flags Only since the 3rd release!!

Unique SDSS moving-object ID (e.g. s0456d) is a coded representation (hash table) of an observation based on SDSS run number and equatorial position on a 1x1 arcsec grid (the limit of 6 digits is stipulated by the Minor Planet Center observation report form). Note that this ID describes SDSS observations, and not physical objects. Thus, the same object can be associated with multiple IDs; one for each SDSS observation.

MJD (TAI) of the mean time during the exposure. If using the first release of SDSS MOC, this record has a different definition.

Johnson V band magnitude is computed from SDSS photometry using

      V = r + 0.44*(g-r) - 0.02

Johnson B band magnitude is computed from SDSS photometry using

      B = V + 1.04*(g-r) + 0.19 
The accuracy of these transformations is better than 0.05 mag (Fukugita et al. 1996, Astronomical Journal, 111, 1748). Recently, an improved set of photometric transformations was made available at the SDSS data release site

Identification for ASTORB file A string of the form ASTORB_YYYYMMDD, where YYYYMMDD is the release date for ASTORB file used in matching.

Identification for file with proper orbital elements A string of the form ASTDYS_?_YYYYMMDD, where YYYYMMDD is the issue date of file used in matching, and ? can be either N (numbered objects) or U (unnumbered objects).

Processing flags set by photometric pipeline. These 64 flags are listed in binary format (0/1) and convey whether an object's detection and subsequent measurements are reliable. For details see Understanding the image processing flags document.

These flags are particularly important when selecting subsamples with peculiar colors, or other measured properties. For example, in a subsample of objects with (g-r) > 1, the MAYBE_CR flag is five times as likely to be set than in the full sample. In order to facilitate such analysis, we also list individual flag statistics for the full sample, and copy verbatim the most relevant portion of the flags document.

Additional Notes:

In all string field values blanks have been replaced with underscores. For example, the designation "1998 RH41" is encoded as "1998_RH41", This allows the record to be read as a series of blank-delimited fields.

All magnitudes that were not properly measured were replaced by 99.99, and all errors that were not properly measured were replaced by 9.99.

In the first version of SDSS MOC, MJD corresponds to the time when row 0 of the r frame was read. To get true mean observation time for an object, add (3.0471e-07 * rowc) days to mjd, where rowc is listed in the catalog (field 6) for each object.

C program for reading SDSSMOC records

To ease the use of a SDSSMOC file, we provide a sample C program, sademo.c which can be used as a template when developing your own processing tools.

To this program, save it first in a file called sademo.c, then compile it as

    cc sademo.c -o sademo
and run it as
    ./sademo filename
where "filename" stands for the catalog file name. The output for file ADR1.dat should look like
> ./sademo ADR1.dat
Parsed file ADR1.dat [58118 lines]
Total moving objects : 58117
Blue                 : 22084
Red                  : 35974
Color unknown        : 59
Identified           : 12602

SM macro for reading SDSSMOC records

For SM users, we provide an SM macro for reading SDSSMOC files.


We thank Princeton University and the University of Washington for generous financial support of this research. We are grateful to E. Bowell for making his ASTORB file publicly available, and to A. Milani, Z. Knezevic and their collaborators for generating and distributing proper orbital elements.


The reference entry for this catalog is Ivezic, Z., Juric, M., Lupton, R.H., Tabachnik, S. & Quinn, T. (the SDSS Collaboration) 2002, Survey and Other Telescope Technologies and Discoveries, J.A. Tyson, S. Wolff, Editors, Proceedings of SPIE Vol. 4836 (2002). In addition, we would greatly appreciate if you add the standard SDSS acknowledgement to your paper:

Funding for the creation and distribution of the SDSS Archive has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Aeronautics and Space Administration, the National Science Foundation, the U.S. Department of Energy, the Japanese Monbukagakusho, and the Max Planck Society. The SDSS Web site is

The SDSS is managed by the Astrophysical Research Consortium (ARC) for the Participating Institutions. The Participating Institutions are The University of Chicago, Fermilab, the Institute for Advanced Study, the Japan Participation Group, The Johns Hopkins University, the Korean Scientist Group, Los Alamos National Laboratory, the Max-Planck-Institute for Astronomy (MPIA), the Max-Planck-Institute for Astrophysics (MPA), New Mexico State University, University of Pittsburgh, University of Portsmouth, Princeton University, the United States Naval Observatory, and the University of Washington.

If you write a paper based on this catalog, please let us know and we will add it to the list of other SDSS-based asteroid publications. This way we will minimize the chance for repeating someone else's work, and will also have a convenient way to access all related papers. The current list is available here.

Thank you very much,

   Zeljko Ivezic (1)
   Mario Juric (2)
   Robert Lupton (2)
   Tom Quinn (1)
   and  the SDSS Collaboration

(1) The University of Washington
(2) Princeton University   

SDSSMOC data files

Each data file has identical format, as described above (apart from the last 64 columns with binary flags, that exist only since the 3rd release). As the new data become available, we will update the list below with additional catalogs.

The latest release: ADR3.dat: the third release (gzip); based on these runs.

The third release is a cumulative release, and it supersedes

the first release and the second release.

Run Lists for Released Catalogs

The files linked below provide basic information about each SDSS observing run used in producing SDSSMOC files. The file names correspond to SDSSMOC file names, with suffix ".dat" replaced by ".runList". Each file has 8 columns that list the run number, run, the starting equatorial position of the (0,0) pixel in camera column 1 (in degrees, RA and Dec), the modified Julian Day for the beginning and the end of the run (MJDstart and MJDend), its node and inclination (in degrees, node and inclination) relative to the equatorial coordinate system (see SDSS EDR paper), and the starting great circle coordinates (so-called mu and nu coordinates, mu is measured along the scan, and nu perpendicularly to the scan) for the (0,0) pixel in camera column 1 (in degrees, mu0 and nu0). The last two quantities are redundant, and can be reproduced using RA, Dec, node, and inclination; they are added for testing coordinate transformations; for convenience, we provide relevant C functions used by SDSS software pipelines.

The sky region covered by a run can be obtained using the above information for the (0,0) pixel in camera column 1, and the layout of the SDSS imaging camera. The nu range spanned by the six camera columns, relative to the (0,0) pixel in camera column 1, is (in degrees):

column    nuMin     nuMax
  1:    0.000000  0.225269
  2:    0.419741  0.645077
  3:    0.839260  1.064554
  4:    1.258912  1.484212
  5:    1.678480  1.903806
  6:    2.098364  2.323656 

ADR1.runList: the run list for ADR1.dat

ADR2.runList: the run list for ADR2.dat

ADR3.runList: the run list for ADR3.dat

Please send us your comments or suggestions.

Version 1.7 from Jan 28, 2005 ( revision history)