Infrared image of the sun

June 2, 1999
Web posted at: 5:00 p.m. EDT (2100 GMT)

CHICAGO (AP) -- It may seem like the sun is just creeping through the heavens, but a new technique for measuring cosmic motion has found that sol is clipping along at an eye-popping 135 miles per second in its orbit of the Milky Way.

Astronomers using a radio telescope system to make the most precise measurement ever of the solar system orbit found that it takes the sun and its family of planets 226 million years to circle the center of its home galaxy.

That means that the last time the sun was at this point in its orbit of the Milky Way, dinosaurs ruled the world and human beings were not yet on the scene.

The new measurement is the most precise value ever determined for one of the fundamental motions of the Earth and its sun, said James Moran of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts. He spoke Tuesday at the national meeting of the American Astronomical Society.

"Our new figure of 226 million years is accurate to within 6 percent," Mark Reid, a Harvard-Smithsonian astronomer and leader of the team that made the measurements, said in a statement.

The sun is one of about 100 billion stars in the Milky Way, one of billions of ordinary galaxies in the universe. The Milky Way is a spiral galaxy, with curving arms of stars pinwheeling out from a center. The solar system is about half way out on one of these arms and is about 26,000 light years away from the center. A light year is about 6 trillion miles.

Reid and his team made the measurement using the Very Long Baseline Array, a system of 10 large radio-telescope antennae placed 5,000 miles across the United States, from the U.S. Virgin Islands in the east, to Hawaii in the west. Working together as a single unit, the antennae are able to measure motions in the distant universe at an unprecedented accuracy.

The accuracy is such that the VLBA can look at a bit of sky that has an apparent size one-ten thousandth the diameter of a human hair held at arms length.

For their solar system measurement, the astronomers focused on Sagittarius A.., a star discovered two decades ago to be at the center of the Milky Way. Over a 10-day period, they measured the apparent shift in position of the star against the background of stars far beyond.

The apparent motion of Sagittarius A.. is very, very small, just one-600,000th of what could be detected with the human eye, the astronomers said.

Reid said the measurement adds supports the idea that at the center of the Milky Way is a supermassive black hole.

"This ... strengthens the idea that this object, much smaller than our own solar system, contains a black hole about 2.6 million times more massive than the sun," Reid said in a statement.

Moran said the new measurement of the solar system orbit adds new accuracy to a fundamental fact of the universe: Everything is moving constantly.

The Earth rotates on its axis at about 1,100 miles an hour, a motion that creates day and night.

The Earth orbits the sun at about 67,000 miles an hour, a motion that takes one year. The sun circles the Milky Way at a speed of about 486,000 miles per hour. And the Milky Way, along with every other galaxy, is moving away from each other, as the universe expands at a constantly accelerating rate.

Copyright 1999   The Associated Press. All rights reserved.