TEST OF LENS-THIRRING ORBITAL SHIFT DUE TO SPIN

The Lense-Thirring effect is a very small shift of the orbit of a test particle due to the spin of a body. It may be described as al orbital drag due to the gravitomagnetic field generated by the spin of the ce ntral body. Gravitomagnetism, a fundamental weak-field prediction of E instein's theory of general relativity, is generated by currents of ma ss and owes its name to its formal analogies with magnetism, generated by currents of electric charge. Then, according to general relativity , the Earth's spin should influence the motion of its orbiting satelli tes. Indeed, we have analysed the laser-ranging observations of the or bits of the satellites LAGEOS and LAGEOS II and have obtained the firs t direct measurement of the Lense-Thirring effect, or 'frame-dragging' , due to the Earth's spin. We measured mu(Lense-Thirring) congruent to 1.1 and estimated the total error delta mu(Lense-Thirring) congruent to +/-0.3, whereas the general relativistic value is mu(Lense-Thirring ) = 1.