The most powerful tool for measuring distances within our Galaxy is the
annual parallax. We carried out phase-referencing VLBI observations of H2​O
masers in the star forming region W3(OH) with respect to the extragalactic
continuum source ICRF 0244+624 to measure their absolute proper motions. The
measured annual parallax is 0.484 ± 0.004 milli-arcseconds which
corresponds to a distance of 2.07^{+0.01}_{-0.02}$ kpc from the sun. This
distance is consistent with photometric and kinematic distances from previous
observations.Comment: Proceedings of the 7th European VLBI Network Symposium (October 12-15
2004, Toledo, Spain), eds. Bachiller, R., Colomer, F., Desmurs, J. F., & de
Vicente, P., 4 pages, 4 figures, needs evn2004.cl