Tracking Gaia with ESO's VLT Survey Telescope (VST)
This image combines ten observations performed on 14 April 2019, using the OMEGACAM instrument with the SDSS-r filter on the VST. Gaia is visible as a line of ten faint dots just below the image centre.
The stars in the image appear as slightly elongated, since the telescope is following Gaia rather than the stars. The observations have been stacked using the stars as reference to show the movement of Gaia across the sky.
Each individual observation was obtained with an exposure time of 60 seconds, and the whole sequence covers about 17 minutes. Astrometric determination of Gaia's position is conducted on each frame, using as reference the coordinates of the background stars as provided in the second Gaia data release (Gaia DR2). The results are then averaged and the resulting value for the position of Gaia has a precision of 20 milliarcseconds or better (one arcsecond is equivalent to the size of a Euro coin seen from a distance of about four kilometres).
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