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Originally published in Science Express on 8 December 2005
Science 6 January 2006:
Vol. 311. no. 5757, pp. 54 - 57
DOI: 10.1126/science.1120914
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Reports

The Distance to the Perseus Spiral Arm in the Milky Way

Y. Xu,1,2,3 M. J. Reid,2 X. W. Zheng,1,2 K. M. Menten4

We have measured the distance to the massive star–forming region W3OH in the Perseus spiral arm of the Milky Way to be 1.95 ± 0.04 kiloparsecs (5.86 x1016 km). This distance was determined by triangulation, with Earth's orbit as one segment of a triangle, using the Very Long Baseline Array. This resolves the long-standing problem that there is a discrepancy of a factor of 2 between different techniques used to determine distances. The reason for the discrepancy is that this portion of the Perseus arm has anomalous motions. The orientation of the anomalous motion agrees with spiral density-wave theory, but the magnitude of the motion is somewhat larger than most models predict.

1 Department of Astronomy, Nanjing University, Nanjing 210093, China.
2 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA.
3 Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 20030, China.
4 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany.

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
The Spiral Structure of the Outer Milky Way in Hydrogen.
E. S. Levine, L. Blitz, and C. Heiles (2006)
Science 312, 1773-1777
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