This photo was taken in December 1972 by the Apollo 17 crew. The spacecraft was traveling between the Earth and the Moon. The reddish landmass is Africa and Saudi Arabia which is desert. The white is both clouds and the ice covering Antarctica.
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Image courtesy of NASA/JPL
Earth--What a Drag!?!
News story originally written on April 1, 1998
The first direct evidence has just been found that shows the Earth does drag quite a bit - it drags space and time around itself as it rotates! This drag effect was predicted 80 years ago using Einstein's
theory of general relativity.
Researchers have been measuring the shifting of two satellites - LAGEOS I and LAGEOS II. LAGEOS stands for Laser Geodynamics Satellite. One of the researchers, Dr. Erricos Pavlis of the Joint Center for Earth System Technology remarked, "We found that the plane of the orbits of LAGEOS I and II were shifted about six feet (two meters) per year in the direction
of the Earth's rotation." This shift is the first direct measurement of the effect called 'frame dragging'.
"General relativity predicts that massive rotating objects should drag space-time around themselves as they rotate," said Pavlis. "Frame dragging is like what happens if a bowling ball spins in a thick fluid such as molasses. As the ball spins, it pulls the molasses around itself. Anything stuck in the molasses will also move around the ball. Similarly, as the Earth rotates, it pulls space-time in its vicinity around itself. This will shift the orbits of satellites near the Earth."
Dr. John Ries, an expert in satellite geodesy at the University of Texas at Austin, cautions that there is a lot of uncertainty involved in the research being done. Certainly, there is more work to be done in this area. The next step will be taken by the LAGEOS III mission.
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