The Lense-Thirring effect, a tiny perturbation of the orbit of a particle caused by the spin of the attracting body, was accurately measured with the use of the data of two laser-ranged satellites, LAGEOS and LAGEOS II, and the Earth gravitational model EGM-96. The parameter &mgr;, which measures the strength of the Lense-Thirring effect, was found to be 1.1 +/- 0.2; general relativity predicts &mgr; identical with 1. This result represents an accurate test and measurement of one of the fundamental predictions of general relativity, that the spin of a body changes the geometry of the universe by generating space-time curvature.

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 an orbital drag due to the gravitomagnetic field generated by the spin of the central body. Gravitomagnetism, a fundamental weak-field prediction of Einstein's theory of general relativity, is generated by currents of mass 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 satellites. Indeed, we have analysed the laser-ranging observations of the orbits of the satellites LAGEOS and LAGEOS II and have obtained the first direct measurement of the Lense-Thirring effect, or 'frame-dragging', due to the Earth's spin. We measured µ Lense−Thirring ∼ = 1.1 and estimated the total error δµ Lense−Thirring ∼ = ±0.3, whereas the general relativistic value is µ Lense−Thirring ≡ 1.

Gravitomagnetism is a fundamental, weak-field, prediction of Einstein's theory of general relativity, is generated by currents of mass and owes its name to its formal analogies with magnetism, generated by currents of electric charge. Then, according to general relativity, Earth's spin should influence the motion of its orbiting satellites. Indeed, we analysed the laser ranging observations of the orbits of the satellites LAGEOS and LAGEOS II and obtained the first direct measurement of the gravitomagnetic orbital perturbation due to the Earth's spin, known as the Lense-Thirring effect.