The Second Release of the Sloan Digital Sky Survey Moving Object Catalog


The Sloan Digital Sky Survey Moving Object Catalog lists astrometric and photometric data for 134,335 moving objects observed prior to March 11, 2003. The catalog also includes orbital elements for 26,847 previously known objects.


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. Some of these data have already been released as a part of the SDSS Early Data Release (EDR). While EDR, and all future releases, will be accessible from the SDSS Archive, it is probably 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 includes 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 upcoming 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.

SDSSMOC will be updated about once a month (i.e. once per every dark run), with a time delay of about 1-3 weeks between the observations and public release. This time delay is mandated by the minimum time needed for data processing and quality assurance procedures.

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. 2002, 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 this catalog is about 90%, and its contamination rate is about 3% (the number of entries that are not moving objects, but rather instrumental artifacts, for details see Paper I). That is, in the first catalog (ADR1.dat, see below) about 6,000 observed moving objects were missed by the processing software, and about 2,000 catalog entries are instrumental and software artifacts.

Post Processing

We matched 58,117 moving objects from ADR1.dat to known objects listed in the ASTORB file (see Paper II), and found 12,602 matches (for 10,592 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. For ADR2.dat, 37,141 observations are matched to objects from ASTORB file, and correspond to 26,847 unique objects. The proper orbital elements are available for 19,963 objects.

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 (30 MB), and a gzip compressed file (6.5 MB), with one record (line) per object observation. 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
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')

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) 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.

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).

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).

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.

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 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, astro-ph/0208099. We would greatly appreciate if you add the following text as an 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, 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, 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 (1,2,3)
   Robert Lupton (1)
   Serge Tabachnik (1)
   Tom Quinn (4)
   and  the SDSS Collaboration

(1) Princeton University 
(2) Zagreb University
(3) Visnjan Observatory
(4) The University of Washington

SDSSMOC data files

Each data file has identical format, as described above. As the new data become available, we will update the list below with additional catalogs.

Subsumed by ADR2.dat!! ADR1.dat: the first release (gzip); based on these runs.

Erratum for ADR1.dat: The 'Proper elements catalog ID' field is incorrect. It should be ASTDYS_N_20010915 and ASTDYS_U_20010915, instead of ASTDYS_N_20000601 and ASTDYS_U_20000601, respectively.

ADR2.dat: the second release (gzip); based on these runs.

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 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

Please send us your comments or suggestions.

Version 3.1 from Jan 24, 2005 ( revision history)