Source designations for objects in 2MASS Catalogs conform to the recommendations outlined in International Astronomical Union's Specifications concerning designations for astronomical radiation sources outside the solar system. Source designations should be given as:
2MASxy Jhhmmss[.]s±ddmmss
The brackets and period are not explicitly in the name, and are shown
above only to illustrate that the last digit before the declination
sign is tenths of RA seconds. The tenths digit is truncated rather
than rounded, per the IAU recommendation.
The x and y in the acronym correspond to characters that
specify the catalog and data release from which the
object was taken, respectively. The acronyms are as follows:
| Acronym | Catalog/Release |
| 2MASSs | For objects in the 2MASS Sampler Point Source Catalog |
| 2MASXs | For objects in the 2MASS Sampler Extended Source Catalog |
| 2MASSI | For objects in the Incremental Release Point Source Catalogs (this release) |
| 2MASXI | For objects in the Incremental Release Extended Source Catalogs (this release) |
| 2MASSW | For objects in the Working Point Source Databases (pre-release) |
| 2MASXW | For objects in the Working Extended Source Databases (pre-release) |
The coordinate sequence is the sexigesimal J2000-equinox RA and declination, hence the "J" designator.
The acronym designation is not carried explicitly for entries in the Catalogs to minimize duplication. The proper designation for objects in the this and all following Incremental Data Releases is 2MASSI and 2MASXI. The coordinate sequence is tabulated for each source and is included in the source record entry in the Catalogs.
A small fraction of sources in the 2MASS First Release Point and Extended Source Catalogs (~0.08%) suffered from a rounding/truncation error in the coordinate name generation algorithm that resulted in time decisecond values of "600" or arcsecond values of "60." The erroneous values exist only in the source designation; the J2000 right ascension and declination supplied for the sources are correct.
The following tables provide the J2000 positions of source in the 2MASS First Release Point and Extended Source Catalogs that have incorrect name designations. For each source, the incorrect designation is given, followed by the corrected name.
Corrected Point Source Catalog Designations
Corrected Extended Source Catalog Designations
[Last Update: 1999 October 5, by R. Cutri]