Earth and Moon

Moon movements

Moon movements

The Moon is a satellite and, therefore, revolves around the Earth at an average distance of 384,400 kilometers, although the actual distance varies along its orbit.

The Moon revolves around its axis (rotation) in approximately 27.32 days (sidereal month) and moves around the Earth (translation) in the same time interval, hence it always shows us the same face.

In addition, our satellite completes a revolution related to the Sun in approximately 29.53 days (synodic month), period in which the lunar phases begin to repeat.

The moments of sunrise, transit and sunset and the Moon are related to the phases. The Moon moves around the Earth in a direct direction, in an East direction. As the Sun moves 1 ° per day to the East.

Rotation and translation of the Moon

The Moon revolves around the Earth approximately once a month. If the Earth did not turn on a full day, it would be very easy to detect the movement of the Moon in its orbit. This movement causes the Moon to advance around 12 degrees in the sky every day.

If the Earth did not rotate, what we would see would be the Moon crossing the celestial vault for two weeks, and then it would go away and take two weeks away, during which the Moon would be visible on the opposite side of the Globe.

However, the Earth completes a turn every day, while the Moon moves in its orbit also to the east. Thus, each day it takes the Earth about 50 more minutes to face the Moon again (which means that we can see the Moon in the Sky.) The Earth's spin and the Moon's orbital movement is they combine, so that the moon's output is delayed on the order of 50 minutes every day.

The Moon-Earth orbit is inclined with respect to the plane of the Earth-Sun orbit, so that only at two points in its path, called nodes, can eclipses of the Sun or Moon be produced.

The orbit of the Moon is complicated, because it is far enough from the Earth to be influenced by the gravity exerted by the Sun. This is why the nodes of the Moon are not fixed, but instead go around in 18.6 years. The axis of the lunar ellipse is also not fixed, which causes the apogee and perigee of the Moon Turn around in 8.85 years.

The inclination of the lunar orbit varies between 5 ° and 5 ° 18 '. To calculate the exact position of the Moon, several hundred terms must be taken into account.

The center of rotation of the Moon with respect to the Earth does not coincide with the axis of the planet, since the Moon also exerts a gravitational attraction on the Earth. If we imagine a rigid bar that joins the centers of both stars, the axis of rotation would be at a point called barycentre, which is located inside the terrestrial globe, about 4,683 km from its center.

Moon libration

To notice the movement of the Moon in its orbit, its location must be taken into account at the time of sunset for a few days. Her orbital movement will take her to a point further east in the sky at twilight every day.

The Moon's own movement translates into a shift from west to east, but its apparent movement occurs from east to west, as a result of the Earth's rotation movement.

The maximum surface of the Moon visible from Earth is not exactly 50% but reaches 59%, for an effect known as libration. The eccentricity of the lunar orbit means that the orbital velocity is not constant and, therefore, parts hidden in the east and west edges can be visible within a month. In this case there is talk of a libration in length. Similarly, there is a libration in latitude as an effect of the inclination of the lunar orbit on the plane of the ecliptic.

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The origin of the moonThe phases of the moon