Abstract
This contribution focuses on the importance of astrometry and on its future developments. Over the centuries astrometry has greatly contributed to the advance of the knowledge of the Universe. Nowadays a major breakthrough is on the way due to astrometric sky surveys from space. ESA space missions Hipparcos first and then Gaia point out the outstanding contribution that space astrometry can provide to our knowledge in many fields of astrophysics, going from the Milky Way formation and evolution, to stellar astrophysics, extra-galactic astrophysics, and fundamental physics. We briefly outline the properties of Gaia first and second data release, and the accuracies expected end-of-mission. The next big advance in space astrometry would be either to improve the astrometric accuracy of one order of magnitude, or to move to a different wavelength domain. While both options have the potential to bring us in a new era of discovery, they have to face enormous issues. We summarize the future directions in space astrometry that are proposed or under investigation by the scientific community, their main challenges and the expected outcome.
Highlights
Astrometry is concerned with the measurements of the positions and motions of celestial objects, going from planets and other Solar system objects, through stars within our Galaxy, to, at least in principle, to galaxies and clusters of galaxies within the Universe
A recent comparison with modern measurements from the Hipparcos satellite shows that both catalogs had an accuracy of the order of 22–30 arcmin (Verbunt and van Gent, 2012)
One of the main outcome of the Hipparcos mission was the definition of a precise celestial reference frame in the optical, i.e., a set of reference stars with precise positions and known proper motions across the celestial sphere, linking together observations done at different locations and different times
Summary
Astrometry is concerned with the measurements of the positions and motions of celestial objects, going from planets and other Solar system objects, through stars within our Galaxy, to, at least in principle, to galaxies and clusters of galaxies within the Universe. One of the main outcome of the Hipparcos mission was the definition of a precise celestial reference frame in the optical, i.e., a set of reference stars with precise positions and known proper motions across the celestial sphere, linking together observations done at different locations and different times. This reference frame is the optical counterpart of the radio reference frame. It lead to a more precise definition of the evolution of the stars (Pietrinferni et al, 2004; Valenti and Fischer, 2005) and of the properties of stellar aggregates in general (Perryman et al, 1998; Kharchenko et al, 2005) and was used to characterize stars orbited by planetary mass companions (Santos et al, 2004)
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