Reid, M. J.M. J.ReidBrunthaler, A.A.BrunthalerMenten, K. M.K. M.MentenYe, XuXuYeXing-Wu, ZhengZhengXing-WuMOSCADELLI, LucaLucaMOSCADELLI2022-12-272022-12-272007978-0521-87464-91743-9213http://hdl.handle.net/20.500.12386/32802Astrometric observations with the VLBA with accuracies approaching ~ 10 μas are being conducted in order to better understand the Galaxy. The location of Sgr A* on infrared images can be determined with an accuracy of a few mas, using stars with SiO maser emission as a calibration grid for infrared images. The apparent proper motion of Sgr A*, which is dominated by the effects of the orbit of the Sun around the Galactic center, has been measured with high accuracy. This measurement strongly constrains Θ<SUB>0</SUB>R<SUB>0</SUB> and offers a dynamical definition of the Galactic plane with Sgr A* at its origin. The intrinsic motion of Sgr A* is very small and comparable to that expected for a supermassive black hole. When combined with infrared results, this provides overwhelming evidence that Sgr A* is a supermassive black hole. Finally, we are engaged in a large project to map the spiral structure and kinematics of the Galaxy. Preliminary trigonometric parallaxes, obtained with the VLBA, to eight massive star forming regions are presented.ELETTRONICOenConference paper10.1017/S17439213070133612-s2.0-38849204211https://www.cambridge.org/core/journals/proceedings-of-the-international-astronomical-union/article/masers-and-galactic-structure-microarcsecond-astrometry-with-the-vlba/9AD7F6C06EBEC5055553D487E2482D40https://api.elsevier.com/content/abstract/scopus_id/388492042112007IAUS..242..348RFIS/05 - ASTRONOMIA E ASTROFISICA