Libration

Definition

Libration is the slight, oscillating motion of the Moon relative to the Earth, which causes different portions of the lunar surface to be visible from the Earth at different times. This phenomenon allows us to see slightly more than 50% of the Moon's surface over the course of the Moon's orbit around the Earth.

5 Must Know Facts For Your Next Test

1. Libration allows us to see approximately 59% of the Moon's total surface area over the course of a lunar cycle.
2. Libration in longitude is caused by the Moon's elliptical orbit, which causes the Moon to appear to rock back and forth from east to west.
3. Libration in latitude is caused by the Moon's tilted axis of rotation relative to its orbit around the Earth, which causes the Moon to appear to tilt back and forth from north to south.
4. The combination of libration in longitude and latitude allows us to see slightly more than 50% of the Moon's surface from Earth.
5. Libration is an important factor in understanding the phases of the Moon and the visibility of lunar features from Earth.

Review Questions

• Explain how libration allows us to see more than 50% of the Moon's surface from Earth.
  • Libration is the slight, oscillating motion of the Moon relative to the Earth, which causes different portions of the lunar surface to be visible at different times. Libration in longitude, caused by the Moon's elliptical orbit, allows us to see slightly more of the eastern and western limbs of the Moon. Libration in latitude, caused by the Moon's tilted axis of rotation, allows us to see slightly more of the northern and southern regions of the Moon. The combination of these two types of libration enables us to observe approximately 59% of the Moon's total surface area over the course of a lunar cycle.
• Describe the relationship between the Moon's elliptical orbit and libration in longitude.
  • Libration in longitude is caused by the fact that the Moon orbits the Earth in an elliptical path, rather than a perfect circle. As the Moon moves closer to and farther from the Earth, its apparent angular velocity changes. When the Moon is closer to the Earth, it moves faster, and when it is farther from the Earth, it moves slower. This difference in angular velocity causes the Moon to appear to rock back and forth, or librate, from east to west, allowing us to see slightly more of the eastern and western limbs of the lunar surface over the course of its orbit.
• Analyze how the combination of libration in longitude and latitude enables us to observe more than 50% of the Moon's surface from Earth.
  • The combination of libration in longitude and latitude allows us to observe approximately 59% of the Moon's total surface area from Earth. Libration in longitude, caused by the Moon's elliptical orbit, enables us to see slightly more of the eastern and western limbs of the lunar surface. Libration in latitude, caused by the Moon's tilted axis of rotation, allows us to see slightly more of the northern and southern regions of the Moon. Together, these two types of libration create a rocking, oscillating motion that reveals different portions of the lunar surface over the course of the Moon's orbit around the Earth. This enables us to observe a greater percentage of the Moon's surface than would be possible if the Moon's rotation and orbit were perfectly synchronized.

Related terms

Lunar Libration: The periodic tilting and rocking of the Moon, which allows us to see slightly more than half of the lunar surface from Earth.

Libration in Longitude: The east-west oscillation of the Moon's visible surface, caused by the Moon's elliptical orbit and the fact that it rotates at a constant rate.

Libration in Latitude: The north-south oscillation of the Moon's visible surface, caused by the Moon's tilted axis of rotation relative to its orbit around the Earth.