Measurement promises complete picture of Milky Way

Astronomers using the National Science Foundation's Very Long Baseline Array (VLBA) have directly measured the distance to a star-forming region on the opposite side of our Milky Way Galaxy from the Sun. Their achievement nearly doubles the previous record for distance measurement within our Galaxy.

"This means that, using the VLBA, we now can accurately map the whole extent of our Galaxy," said Alberto Sanna, of the Max-Planck Institute for Radio Astronomy (MPIfR) in Germany.

Distance measurements are crucial for understanding the structure of the Milky Way. Most of our Galaxy's material, consisting principally of stars, gas, and dust, lies within a flattened disk, in which our Solar System is embedded. Because we can't see our Galaxy face-on, its structure, including the shape of its spiral arms, can only be mapped by measuring distances to objects elsewhere in the Galaxy.

The astronomers used a technique called trigonometric parallax, first used in 1838 to measure the distance to a star. This technique measures the apparent shift in the sky position of a celestial object as seen from opposite sides of Earth's orbit around the Sun. This effect can be demonstrated by holding a finger in front of one's nose and alternately closing each eye -- the finger appears to jump from side to side.

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