Radio astronomers say sun travels 135 miles per second around Milky
Copyright � 1999 Nando Media
Copyright � 1999 Associated Press
By PAUL RECER
CHICAGO (June 2, 1999 11:04 a.m. EDT http://www.nandotimes.com) - 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
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, Mass.
He spoke Tuesday at the national meeting of the American Astronomical
"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
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
The apparent motion of Sagittarius A* is very, very small, just
one-600,000th of what could be detected with the human eye, the
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
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.