Gaia in the UK

Taking the Galactic Census

Gaia Data Release 2

Numbers of GDR2 stars in different categories.

How many stars will there be in the second Gaia data release? The image shows numbers of stars in different categories included in Gaia DR2. Additional information can be found in article How many stars to expect in Gaia's second data release on ESA website. Image credit: ESA, CC BY-SA 3.0 IGO. Download larger image (506 KB).

Gaia Data Release 2 was released on 25 April 2018. Description of the contents of Gaia DR2 is given below. For more information visit Gaia Data Release 2 page on the European Space Agency website.

Gaia DR2 data is based on data collected between 25 July 2014 (10:30 UTC) and 23 May 2016 (11:35 UTC), spanning a period of 22 months of data collection (or 668 days), as compared to Gaia DR1 which was based on observations collected in the first 14 months of Gaia's routine operational phase.

The reference epoch for Gaia DR2 is J2015.5 (with respect to the J2015.0 epoch for Gaia DR1). Positions and proper motions are referred to the ICRS, to which the optical reference frame defined by Gaia DR2 is aligned. The time coordinate for Gaia DR2 results is the barycentric coordinate time (TCB).

Contents of Gaia DR2

  • The five-parameter astrometric solution - positions on the sky (α, δ), parallaxes, and proper motions - for more than 1.3 billion (109) sources, with a limiting magnitude of G = 21 and a bright limit of G ≈ 3. Parallax uncertainties are in the range of up to 0.04 milliarcsecond for sources at G < 15, around 0.1 mas for sources with G=17 and at the faint end, the uncertainty is of the order of 0.7 mas at G = 20. The corresponding uncertainties in the respective proper motion components are up to 0.06 mas yr-1 (for G < 15 mag), 0.2 mas yr-1 (for G = 17 mag) and 1.2 mas yr-1 (for G = 20 mag). The Gaia DR2 parallaxes and proper motions are based only on Gaia data; they do no longer depend on the Tycho-2 Catalogue.
  • Mean radial velocities (i.e. the median value over the epochs) for more than 7.2 million stars with a mean G magnitude between about 4 and 13 and an effective temperature (Teff) in the range of about 3550 to 6900 K. This leads to a full six-parameter solution: positions and motions on the sky with parallaxes and radial velocities, all combined with mean G magnitudes. The overall precision of the radial velocities at the bright end is in the order of 200-300 m s-1 while at the faint end the overall precision is approximately 1.2 km s-1 for a Teff of 4750 K and about 2.5 km s-1 for a Teff of 6500 K.
  • An additional set of more than 361 million sources for which a two-parameter solution is available: the positions on the sky (α, δ) combined with the mean G magnitude. These sources have a positional uncertainty at G=20 of about 2 mas, at J2015.5.
  • G magnitudes for more than 1.69 billion sources, with precisions varying from around 1 millimagnitude at the bright (G<13) end to around 20 millimagnitudes at G=20. Please be aware that the photometric system for the G band in Gaia DR2 will be different from the photometric system as used in Gaia DR1.
  • GBP and GRP magnitudes for more than 1.38 billion sources, with precisions varying from a few millimagnitudes at the bright (G<13) end to around 200 millimagnitudes at G=20.
  • Full passband definitions for G, BP and RP. These passbands are now available for download. For a detailed description see Gaia DR2 passbands.
  • Epoch astrometry for 14,099 known solar system objects based on more than 1.5 million CCD observations. 96% of the along-scan (AL) residuals are in the range -5 to 5 mas, and 52% of the AL residuals are in the range of -1 to 1 mas. The are part of Gaia DR2 and have also been delivered to the Minor Planet Center (MPC).
  • Subject to limitations (see Gaia Data Release 2) the effective temperatures Teff for more than 161 million sources brighter than 17th magnitude with effective temperatures in the range 3000 to 10,000 K. For a subset of about 87 million sources also the line-of-sight extinction AG and reddening E(BP-RP) are given and for a part of this subset (around 76 million sources) the luminosity and radius are available as well.
  • Classifications for more than 550,000 variable sources consisting of Cepheids, RR Lyrae, Mira and Semi-Regular Candidates as well as High-Amplitude Delta Scuti and SX Phoenicis Candidates and short time scale phenomena.
  • Planned cross-matches between Gaia DR2 sources on the one hand and Hipparcos-2, Tycho-2, 2MASS PSC, SDSS DR9, Pan-STARRS1, GSC2.3, PPM-XL, AllWISE, and URAT-1 data on the other hand.

Comparison of DR1 and DR2 contents

The table below shows a comparison of the Gaia Data Release1 and Gaia Data Release 2 in numbers:

 Number of
sources in Gaia DR2 
Number of
sources in Gaia DR1
Total number of sources   1,692,919,1351,142,679,769
Number of 5-parameter sources 1,331,909,7272,057,050
Number of 2-parameter sources 361,009,4081,140,622,719
Sources with mean G magnitude1,692,919,1351,142,679,769
Sources with mean GBP-band photometry1,381,964,755-
Sources with mean GRP-band photometry 1,383,551,713-
Sources with radial velocities 7,224,631-
Variable sources 550,7373,194
Known asteroids with epoch data 14,099-
Gaia-CRF extra-galactic sources (optical reference frame)556,8692,191
Effective temperatures (Teff161,497,595-
Extinction (AG) and reddening (E(GBP-GRP)) 87,733,672-
Sources with radius and luminosity 76,956,778-

Credit: ESA and the Gaia Data Processing and Analysis Consortium.

Gaia DR2 data model, passbands and auxiliary data

To help with the preparations for the second data release Gaia Data Processing and Analysis Consortium released the Gaia DR2 data model. Available for download as well are Gaia DR2 passbands. These are described in Gaia image of the week. For other auxiliary data see Auxiliary Data page on ESA's website. 

Gaia DR2 data

The Gaia DR2 data can be accessed at:

Gaia data can also be downloaded directly in CSV format from .

Help information on the use of Astronomical Data Query Language (ADQL) can be found at:

Gaia DR2 resources

Listing of Gaia DR2 resources can be found on . The link to the livestream of the press event will be provided on this page once known on 25 April.

"Gaia DR2 primer" (PDF, 1.1 MB), written by the Gaia Helpdesk with the aim of  collecting all information, tips and tricks, pitfalls, caveats, and recommendations relevant to Gaia’s second data release (Gaia DR2) in one place and to provide pointers to where more detailed information can be found.

Gaia DR2 Astronomical Data Query Language (ADQL) validator is available. The service will not allow access to DR2 data before the release on 25 April, but it can already be used to check the syntax and the schema/table/column names.

"Gaia Data Release 2: A guide for scientists" videos:

Gaia DR2 Gaia Sky videos: A series of videos made with Gaia Sky using Gaia Data Release 2 data, available from . Included are: Comparison of the Gaia DR1 TGAS catalogue with the new Gaia DR2 catalogue, Demonstration of parallaxes and proper motion in the northern sky, Demonstration of parallaxes and proper motions - 360 degrees video, Demonstration of the LMC rotation, Tour through the Gaia DR2 asteroids.

Gaia Data Release 2: In-depth stories:

Gaia DR2 papers

Several papers have been published on the data processing and validation performed by the different coordination units in the Gaia Data Processing and Analysis Consortium (DPAC), performance verification of Gaia, and providing basic demonstrations of the scientific potential of the Gaia DR2 catalogue. For more information about Gaia DR2 papers see Gaia Data Release 2 papers.

Summary papers

Description of the Gaia mission (spacecraft, instruments, survey and measurement principles)
Gaia Collaboration, Prusti, T., et al. (2016)

Gaia Data Release 2: Summary of the contents and survey properties, Gaia Collaboration, Brown, A.G.A., et al. (arXiv: 1804.09365)

Processing papers

Gaia Data Release 2: The astrometric solution, Lindegren, L., et al. (arXiv: 1804.09366)

Gaia Data Release 2: Calibration and mitigation of electronic offset effects in Gaia data, Hambly, N., et al. (arXiv: 1804.09830)

Gaia Data Release 2: Processing of the photometric data, Riello, M., et al. (arXiv: 1804.09367)

Gaia Data Release 2: The photometric content and validation, Evans, D.W., et al. (arXiv: 1804.09368)

Gaia Data Release 2: The Gaia Radial Velocity Spectrometer, Cropper, M., et al. (arXiv: 1804.09369)

Gaia Data Release 2: The catalogue of radial velocity standard stars, Soubiran, C., et al. (arXiv: 1804.09370)

Gaia Data Release 2: Processing, validation and performance of the spectroscopic data, Sartoretti, P., et al. (arXiv: 1804.09371)

Gaia Data Release 2: Properties and validation of the radial velocities, Katz, D., et al. (arXiv: 1804.09372)

Gaia Data Release 2: Summary of variability processing and analysis results, Holl, B., et al. (arXiv: 1804.09373)

Gaia Data Release 2: First stellar parameters from Apsis, Andrae, R., et al. (arXiv: 1804.09374)

Gaia Data Release 2: Catalogue validation, Arenou, F., et al. (arXiv: 1804.09375)

Gaia Data Release 2: Cross-match with external catalogues: algorithm and statistics, Marrese, P.M., et al. (arXiv: 1808.09151 )

Gaia Data Release 2: Using Gaia parallaxes (PDF, 7.3 MB), Luri, X., et al. (arXiv: 1804.09376)

Performance verification papers

Gaia Data Release 2: The celestial reference frame (Gaia-CRF2), Gaia Collaboration, Mignard, F., et al. (arXiv: 1804.09377)

Gaia Data Release 2: Observational Hertzsprung-Russell diagrams, Gaia Collaboration, Babusiaux, C., et al. (arXiv: 1804.09378)

Gaia Data Release 2: Observations of Solar System objects, Gaia Collaboration, Spoto, F., et al. (arXiv: 1804.09379)

Gaia Data Release 2: Mapping the Milky Way disk kinematics, Gaia Collaboration, Katz, D., et al. (arXiv: 1804.09380)

Gaia Data Release 2: The kinematics of globular clusters and dwarf galaxies around the Milky Way, Gaia Collaboration, Helmi, A., et al. (arXiv: 1804.09381)

Gaia Data Release 2: Variable stars in the Colour-Magnitude Diagram, Gaia Collaboration, Eyer, L., et al. (arXiv: 1804.09382)


Page last updated: 07 December 2023