The Milky Way, the galaxy among whose 200 billion stars is the sun, is only about 70 percent as big as astronomers used to think and the sun is much closer to the center than was previously estimated.

The revised measurements emerged from a new, more accurate method of estimating distances in space. The old method relied on measurements of the brightness of distant celestial objects but suffered from the fact that stars near the galactic center are obscured by clouds of gas and dust. The new method makes use of an ability to detect unusual regions of gas and dust near the galactic center where stars are being born.

The region contains objects called water masers that emit a detectable radiation and that are moving both laterally and toward the Earth. By measuring these motions with widely separated radio telescopes, as far apart as Massachusetts and California, and using a kind of triangulation, astronomers found the Milky Way is not 100,000 light years across but a mere 70,000 light years. The sun, thought for decades to be 33,000 light years from the center, is actually only 23,000 light years away. A light year, the distance light travels in one year, is about 6 trillion miles.

The findings, announced by the National Science Foundation, were made by a team led by Mark J. Reid of the Smithsonian Astrophysical Observatory in Cambridge, Mass.