2026-10-14T21:53:29Zhttps://gaia.aip.de/oai/oai:gaia.aip.de:schemas/gaiadr12019-10-01schemas10.17876/gaia/dr.1Gaia DR1European Space Agency (ESA)DPAC ConsortiumAstronomyLeibniz Institute for Astrophysics Potsdam (AIP)<h3>Update</h3>
<p>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>.</p>
<h4>Content of DR1</h4>
<ul>
<li>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").</li>
<li>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).</li>
<li>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.</li>
<li>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.</li>
</ul>
Gaia DR1 is based on observations collected between 25 July 2014 and 16 September 2015.
<img style="width: 100%;" src="https://gaia.aip.de/cms/wp-content/uploads/2017/02/gdr1_density_map.png" alt="Density map for gaiadr1.gaia_source (number of sources per square degree). Healpix based (nside 512, 3.14Mpixels) " />
<i>Density map for gaiadr1.gaia_source (number of sources per square degree). Healpix based (nside 512, 3.14Mpixels)</i>
<h4>Source numbers</h4>
<table class="table table-bordered">
<tbody>
<tr>
<td>Total number of sources</td>
<td>1,142,679,769</td>
</tr>
<tr>
<td>Number of TGAS* sources</td>
<td>2,057,050</td>
</tr>
<tr>
<td>- Hipparcos</td>
<td>93,635</td>
</tr>
<tr>
<td>- Tycho-2</td>
<td>1,963,415</td>
</tr>
<tr>
<td>Number of secondary sources**</td>
<td>1,140,622,719</td>
</tr>
<tr>
<td>Number of light curves for Cepheids</td>
<td>599</td>
</tr>
<tr>
<td>Number of light curves for RR Lyrae</td>
<td>2595</td>
</tr>
</tbody>
</table>
<h4>Magnitude distribution percentiles (G)</h4>
<table class="table table-bordered">
<tbody>
<tr>
<td>0.135%</td>
<td>11.2</td>
</tr>
<tr>
<td>2.275%</td>
<td>14.5</td>
</tr>
<tr>
<td>15.866%</td>
<td>17.1</td>
</tr>
<tr>
<td>50%</td>
<td>19.0</td>
</tr>
<tr>
<td>84.134%</td>
<td>20.1</td>
</tr>
<tr>
<td>97.725%</td>
<td>20.7</td>
</tr>
<tr>
<td>99.865%</td>
<td>21.0</td>
</tr>
</tbody>
</table>
<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: <a href="http://www.cosmos.esa.int/web/gaia/dr1">http://www.cosmos.esa.int/web/gaia/dr1</a>2016-09-14BY_NC_IGDataset