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Space astrometry
Perryman, Michael
Astrometry, the measurement of accurate star positions and motions, was first carried out from space by the European Space Agency's Hipparcos mission in the 1990s. Today, it is undergoing a particularly dramatic advance with ESA's ongoing Gaia mission, launched in 2013. I explain why star positions are of such importance in astronomy, and outline …
Interstellar objects
Moro-Martín, Amaya; Seligman, Darryl Z.
Since 2017, two macroscopic interstellar objects have been discovered in the inner Solar System, both of which are distinct in nature. The first interstellar object, 1I/`Oumuamua, passed within $\sim63$ lunar distances of the Earth, appeared asteroidal lacking detectable levels of gas or dust loss, yet exhibited a nongravitational acceleration. 1I…
Gaia: 3-dimensional census of the Milky Way Galaxy
Gilmore, Gerard
Astrometry from space has unique advantages over ground-based observations: the all-sky coverage, relatively stable, and temperature and gravity invariant, operating environment delivers precision, accuracy and sample volume several orders of magnitude greater than ground-based results. Even more importantly, absolute astrometry is possible. The E…