Gaia DR1

Update

In order to be consistent with the naming of the ESAC Archive the name of the schema (database) holding the data of Gaia data release 1 has been modified on the 3rd of December 2020 from <code>gdr1</code> to <code>gaiadr1</code>.

Content of DR1

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.

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

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

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

<em>** 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).</em>

Source: http://www.cosmos.esa.int/web/gaia/dr1