Gaia Data Release 1 (GDR1)


  • Positions (α, δ) and G magnitudes for all sources with acceptable formal standard errors on positions. Positions and individual uncertainties are computed using a generic prior and Bayes’ rule (detailed description in “Gaia astrometry for stars with too few observations. A Bayesian approach”).
  • The five-parameter astrometric solution – positions, parallaxes, and proper motions – for stars in common between the Tycho-2 Catalogue and Gaia is contained in Gaia DR1. This part of Gaia DR1 is based on the Tycho-Gaia Astrometric Solution (Image of the Week with short TGAS description; paper with a more detailed description; paper describing theory and background; paper describing quasar extension).
  • At the beginning of the routine phase, for a period of 4 weeks, a special scanning mode repeatedly covering the ecliptic poles on every spin was executed for calibration purposes. Photometric data of selected RR Lyrae and Cepheid variable stars including these high-cadence measurements are contained in Gaia DR1.
  • Positions (α, δ) and G magnitudes for 2152 ICRF quasars (F. Mignard et al., 2016).
    Cross-matches will be provided between Gaia sources on the one hand and Hipparcos-2, Tycho-2, 2MASS PSC, GSC2.3, PPM-XL, UCAC-4, SDSS DR10 / DR12, AllWISE, and URAT-1 data on the other hand.

Gaia DR1 is based on observations collected between 25 July 2014 and 16 September 2015.

Density map for gaiadr1.gaia_source (number of sources per square degree). Healpix based (nside 512, 3.14Mpixels)

**Source numbers**
Total number of sources 1,142,679,769
Number of TGAS* sources 2,057,050
– Hipparcos 93,635
– Tycho-2 1,963,415
Number of secondary sources** 1,140,622,719
Number of light curves for Cepheids 599
Number of light curves for RR Lyrae 2595

Magnitude distribution percentiles (G)

0.135% 11.2
2.275% 14.5
15.866% 17.1
50% 19.0
84.134% 20.1
97.725% 20.7
99.865% 21.0

* TGAS = Tycho-Gaia Astrometric Solution, also referred to as primary solution for primary sources.

** The astrometric solution of secondary sources (non-TGAS sources) is derived using the calibrations of the spacecraft attitude and the geometry of the instrument as `fixed’ input, as derived from the astrometric solution of primary sources (i.e., the TGAS solution).