We conducted the astrometry of H _ { 2 } O masers in the Galactic star-forming region Onsala 1 ( ON1 ) with VLBI Exploration of Radio Astrometry ( VERA ) .
We measured a trigonometric parallax of 0.404 \pm 0.017 mas , corresponding to a distance of 2.47 \pm 0.11 kpc .
ON1 is appeared to be located near the tangent point at the Galactic longitude of \timeform 69.54D .
We estimate the angular velocity of the Galactic rotation at Sun , the ratio of the distance from Sun to the Galactic center and the Galactic rotation velocity at Sun , to be \Omega _ { 0 } = \Theta _ { 0 } / R _ { 0 } = 28.7 \pm 1.3 km s ^ { -1 } kpc ^ { -1 } using the measured distance and proper motion of ON1 .
This value is larger than the IAU recommended value of 220 km s ^ { -1 } /8.5 kpc = 25.9 km s ^ { -1 } kpc ^ { -1 } , but consistent with other results recently obtained with the VLBI technique .