Triangulating the Galaxy.

GALAXIES; GALACTIC center; INTERSTELLAR medium; ASTRONOMERS; ASTRONOMY; ARTIFICIAL satellites; ORBITS (Astronomy); EUROPEAN Space Agency; MILKY Way

The article informs that measurements of a maser in the Milky Way allow precise determination of astronomical distances and should improve estimates of the fraction of dark matter in the galaxy. Astronomers can make physical sense of the heavens only if they know the distances to objects, so any advance in distance measurement is important. Ultimately all astronomical distances depend on triangulation as people measure two angles in a triangle formed by lines of sight to an astronomical object from two points of known separation. In the late 1990s, the European Space Agency's Hipparcos satellite revolutionized parallax measurements by determining the parallaxes of several thousand stars to a precision of about one milli-arc second, equivalent to 5 x 10-9 radian, which is sufficient to obtain reliable distances for objects closer than about 100 pc. Doppler measurements of the line-of-sight velocity of this region, together with the assumption that it is on a circular orbit around the galactic center, yield a distance of 4.2 kpc, nearly twice as great as the distance estimated from the brightness of some of the region's stars.