A satellite's ground track shows the path of its orbit on the surface of the parent body. Lunar Reconnaissance Orbiter will be placed in a nearly circular polar orbit about 50 kilometers (31 miles) above the surface of the Moon, completing each orbit in a little less than two hours. The orientation of this orbit remains fixed in space, relative to the stars, while the Moon slowly rotates beneath it as they travel together around the Earth, allowing LRO to scan the entire surface of the Moon every two weeks.
The animation depicts LRO's ground track over a period of 27.3 days (348 orbits) or one sidereal month, the amount of time it takes the Moon to turn once on its axis, relative to the stars. This is two days shorter than the synodic month, the period of the Moon's phases. The difference arises from the motion of the Earth. While the Moon is orbiting the Earth, the Earth is carrying them both around the Sun, changing the Sun's direction relative to the stars.
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