The most powerful tool for measuring distances within our Galaxy is the annual parallax .
We carried out phase-referencing VLBI observations of H _ { 2 } 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 \pm 0.004 milli-arcseconds which corresponds to a distance of 2.07 \mbox { } ^ { +0.01 } _ { -0.02 } kpc from the sun .
This distance is consistent with photometric and kinematic distances from previous observations .