Size of Milky Way 25% Smaller, New Geometric Measure Shows

Astronomers using a new technique to figure distances have found that the Milky Way, the collection of stars that includes the sun, is more than 25% smaller than previously believed, the National Science Foundation said Monday.

The new measurements, expected to have a major impact on many aspects of astronomy, also show that the sun and its planets are much closer to the center of the galaxy than previously thought.

The foundation, which sponsored much of the work, said that an international team of scientists used advanced geometry for the first time to measure distances from certain reference points in the galaxy.

Previously, distances from the center of the galaxy were determined by measuring variations in the brightness of celestial objects, a less precise method, the foundation said.

Mark J. Reid, a radio astronomer with the Smithsonian Astrophysical Observatory in Cambridge, Mass., reported that the geometric technique found the sun to be 23,000 light years from the center of the galaxy.

For more than two decades, this distance was thought to be up to 33,000 light years.

The new measurements also reduce the size of the Milky Way, a spiral-shaped disk of 200 billion stars, from a generally accepted diameter of 100,000 light years to about 70,000 light years, Reid reported.

A light year is the distance light, traveling at 186,000 miles per second in a vacuum, covers in a year’s time--about 6 trillion miles.

The bulging center of the Milky Way, from which spiral arms of stars swing out, is obscured from the sun by billions of tons of dust and gas. This makes it hard to measure the distance from the center by using the brightness of objects, the researchers said.

To make the new measurements possible, scientists needed a reference point from which to judge distances. This proved to be a recently discovered region of newly formed stars near the galactic center, they said.