The Moon's orbit around Earth has many variations (perturbations) due to the gravitational attraction of the Sun and planets, the study of which (lunar theory) has a long history.

[citation needed] Since nearer objects appear larger, the Moon's apparent size changes as it moves toward and away from an observer on Earth.

An event called a "supermoon" occurs when the full Moon is closest to Earth (perigee).

The variance in the Moon's orbital distance corresponds with changes in its tangential and angular speeds, per Kepler's second law.

The mean angular movement relative to an imaginary observer at the Earth–Moon barycentre is 13.176° per day to the east (J2000.0 epoch).

The lunar orbit's major axis – the longest diameter of the orbit, joining its nearest and farthest points, the perigee and apogee, respectively – makes one complete revolution every 8.85 Earth years, or 3,232.6054 days, as it rotates slowly in the same direction as the Moon itself (direct motion) – meaning precesses eastward by 360°.

Theoretical considerations show that the present inclination relative to the ecliptic plane arose by tidal evolution from an earlier near-Earth orbit with a fairly constant inclination relative to Earth's equator.

It is thought that originally the inclination to the equator was near zero, but it could have been increased to 10° through the influence of planetesimals passing near the Moon while falling to the Earth.

Therefore, the angle between the ecliptic and the lunar equator is always 1.543°, even though the rotational axis of the Moon is not fixed with respect to the stars.

Conversely, 9.3 years later, the angle between the Moon's orbit and Earth's equator reaches its minimum of 18°20′.

At that time the descending node was lined up with the equinox (the point in the sky having right ascension zero and declination zero).

When the inclination is at its maximum of 28°36', the centre of the Moon's disk will be above the horizon every day only from latitudes less than 60°27' (90° − 28°36' – 57' parallax) north or south.

Note that a point on the Moon can actually be visible when it is about 34 arc minutes below the horizon, due to atmospheric refraction.

When the Sun is the furthest below the horizon (winter solstice), the Moon will be full when it is at its highest point.

Babylonian astronomy discovered the three main periods of the Moon's motion and used data analysis to build lunar calendars that extended well into the future.

[7] This use of detailed, systematic observations to make predictions based on experimental data may be classified as the first scientific study in human history.

Ancient Greek astronomers were the first to introduce and analyze mathematical models of the motion of objects in the sky.

[14] The sidereal month is the time it takes to make one complete orbit around Earth with respect to the fixed stars.

This slightly greater orbital angular momentum causes the Earth–Moon distance to increase at approximately 38 millimetres per year.

[17] Conservation of angular momentum means that Earth's axial rotation is gradually slowing, and because of this its day lengthens by approximately 24 microseconds every year (excluding glacial rebound).

[19] The Moon is gradually receding from Earth into a higher orbit, and calculations suggest that this would continue for about 50 billion years.

However, the slowdown of Earth's rotation is not occurring fast enough for the rotation to lengthen to a month before other effects change the situation: approximately 2.3 billion years from now, the increase of the Sun's radiation will have caused Earth's oceans to evaporate,[22] removing the bulk of the tidal friction and acceleration.

At that time the Moon is a bit ahead in its orbit with respect to its rotation about its axis, and this creates a perspective effect which allows us to see up to eight degrees of longitude of its eastern (right) far side.

Conversely, when the Moon reaches its apogee, its orbital motion is slower than its rotation, revealing eight degrees of longitude of its western (left) far side.

The Moon's axis of rotation is inclined by in total 6.7° relative to the normal to the plane of the ecliptic.

This gives rise to a diurnal libration, which allows one to view an additional one degree's worth of lunar longitude.

For the same reason, observers at both of Earth's geographical poles would be able to see one additional degree's worth of libration in latitude.

This could give the impression that the Moon orbits Earth in such a way that sometimes it goes backwards when viewed from the Sun's perspective.

The path of the Earth–Moon system in its solar orbit is defined as the movement of this mutual centre of gravity around the Sun.