Basic solar system measure redefined

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BEIJING, Sept. 17 (UPI) -- Astronomers meeting in Beijing say they've agreed on a new definition of the fundamental unit of distance between objects in the solar system.

The "astronomical unit," defined as the distance between the sun and the Earth, is now set at exactly 149,597,870,700 meters (163,602,220,800.53 yards or 92,955,807.27 miles), the meeting of the International Astronomical Union declared.

That's 9 meters, or about 30 feet, more than the previously agreed distance, which was based on the average distance between Earth and the sun and was also tied to the mass of the sun.

But the sun is constantly losing mass as it radiates energy, which technically changes the value of the AU over time, astronomers said.

"The old definition was good when we were not able to measure distance precisely in the solar system," Sergei Klioner of the Technical University of Dresden, Germany, who has been calling for the change since 2005, told NewScientist.com.

But scientists can now make precise measurements of astronomical distances using lasers and space probes.

"I've been teaching celestial mechanics for 20 years and it was always a pain to explain the old definition," Klioner said. "It was clear that it was unnecessarily complicated."