Patterns of the Moon

The Moon orbits the Earth about once a month while the Earth orbits beneath it every day, and together the Earth and Moon orbit the Sun once a year. The relative positions of the Sun and stars change slowly during the Earth-Moon system's annual orbit around the Sun, but from our point of view on the Earth's surface, objects in the sky appear to rise, crossing the sky from this to towards the west and is located below the horizon due to the direction in which the Earth rotates each day. This daily movement is the most notable and dominates our perception of the sky.

In reality, the Moon orbits the Earth from west to east, so it slowly appears to slide backward relative to the perceived daily motion of the sky as the Earth rotates. This causes the Moon to rise a little later each day for about a month, so it will go from being on the side of the Earth facing the Sun to the opposite side facing away from it and vice versa. From Earth we can only see part of the portion of the Moon illuminated by the Sun depending on its position in the sky with respect to the Sun and this produces the cycle of lunar phases.

These range from the full

moon

when we see the entire illuminated side of the lunar surface on the opposite side of the sky from the sun, to the new

moon

when the illuminated part is completely away from the Earth and the moon is very close. to the sun in the sky. Just before and after the new moon, a thin crescent is seen, as only a small part of the illuminated portion of the moon is at an angle that can be seen from Earth. As the Moon orbits the Earth, over time more and more illuminated surface will be visible, appearing to increase from the western edge of the Moon until it is full, and then disappearing again from the westernmost edge until it is new.

The plane in which the Moon orbits the Earth is very similar to the plane in which the Earth orbits the Sun. Because the axis around which the Earth rotates is tilted with respect to this plane, the place where it rises and sets The sun, its path across the sky, and its position relative to the stars change a small amount each day in a pattern that repeats itself over the course of a year. The moon appears to follow this same pattern over the course of about a month. Although the Moon is much closer to the Earth than the Sun and orbits the Earth rather than the other way around, from the Earth's surface the

patterns

of its motion in the sky appear to operate in very similar ways.

Just as the sun may appear centered more in the northern or southern part of the Earth and appear higher or lower in the sky for more or fewer hours each day, the position of the moon also changes and much more rapidly. The place on the horizon where the moon rises on a particular day or night oscillates rapidly from a peak north of east to a peak south of east and back again over the course of about a month. The position changes most rapidly towards the middle of the movement and decelerates at any maximum before receding. Although the moon can rise or set at any point on the horizon within its monthly north-south range, it is difficult to observe it at any specific position on the horizon except during deceleration at maxima.

These slowing and stopping events of the sun are called solstices from the Latin "sun" and "stop" and the corresponding monthly positions of the moon may be called lunistices or, more commonly, lunar stops. There is a North Stop when the moon rises and sets at a maximum point towards the north and a South Stop when it rises and sets towards the south. Over the course of a year, the phase of the moon during which maxima are reached changes in turn due to the changing relative positions of the sun, moon, and Earth. For example, the full moon is always opposite the sun, so as the sun approaches its northernmost position, a full moon that occurs around that time will be located far to the south, but the exact timing of the sun On the solstice, a monthly lunar stop and a specific phase of the moon will not always coincide.

The Earth's tilt has been decreasing over the past few thousand years, so today's peak positions are slightly less extreme than in the past. In addition to this small change, the maximum positions of the sun on the horizon are repeated year after year. If the same pattern is followed for the Moon for a few months, it may also appear to repeat itself, but if followed for several years, the Moon's maximum positions will end up being more extreme than the Sun's positions at the solstices. Many ancient cultures marked the sun's annual range at solstices, and there is evidence that some followed the moon's

patterns

of immobility.

When the Moon's monthly maximum stop positions to the north and south reach a maximum extreme, this is called a major lunar stop. Although there is an exact maximum position of the Moon at any given time during a major lunar standstill, the extreme positions change very little for about a year on either side of the exact maximum, so the Moon in one phase or another will reach the closest position. northern. and southern highs once a month. To distinguish the exact positions, one end may be called the Northern Major Lunar Stop and the other the Southern Major Lunar Stop.

After a few more years pass, the moon's maximum positions each month will become noticeably less extreme until they reach the same range as the sun on the solstice and then continue to decline over the years until the moon's monthly maximum positions moon reach a minimum range. At this point, the monthly north-south swing will be less than the range of the sun at the solstices and this is called a minor lunar stop. To define the rising and setting positions at this point, we distinguish a southern minor lunar stop and a northern minor lunar stop. The highs will continue to rise again until they reach the most extreme positions at the next major lunar stop during a cycle of 18.6 years from one major lunar stop to the next.

The minor lunar stop occurs halfway through the cycle, around 9.3 years, and approximately halfway between a minor lunar stop and a major lunar stop, the maximum points of moonrise each month will coincide with those reached by the sun. every year at the solstices. These additional divisions have not received much attention since they overlap with the same positions as the sun at the solstices, but since those positions were important to some ancient observers, when the moon reached the same positions they probably would have at least paid some attention. . These points in the cycle could be called Equalized Lunar Stops, one with maximum positions increasing from a Minor Lunar Stop to a Major Lunar Stop, and another with positions decreasing from a Major Lunar Stop to a Minor Lunar Stop.

The northern equalized lunar stop and the southern equalized lunar stop can be used to distinguish the range of the monthly oscillation as with other points in the cycle. The reason the Moon's extreme positions constantly change is related to the plane in which the Moon orbits the Earth. Although this plane is very similar to the plane in which the Earth orbits the Sun at an inclination of 23.4°, the Moon orbits the Earth in a plane that is inclined 5.1° more and this orbit precedes so that the highest point and the lowest point of the orbit changes its orientation in space and takes 18.6 years to return to the same orientation.

When the highest point of the Moon's orbital plane coincides with the orientation of the Earth's inclination relative to the plane in which it orbits the Sun, the additional inclination of the Moon's orbit is added to the inclination of the Moon's orbit. Earth, allowing the Moon to reach more extreme positions towards the northern or southern part of the Earth relative to the equator and, as a result, it can appear higher or lower in the sky and reach more extreme positions on the horizon every month for the duration of this orientation. As the cycle continues and the orientation of the moon's orbit precedes toward the opposite orientation, it passes through a point where the effect cancels out so that the monthly maximum positions of the moon are equal to the annual maximum positions of the sun.

Finally, the high and low points of the lunar orbit reach an orientation where they are located opposite the maximum and minimum points defined by the Earth's tilt, limiting the Moon's monthly range to a minimum to produce a Stop. Minor mole. The orbit then retreats through the mid-ranges until it reaches the position again to produce the extremes of a major lunar standstill. The two points where the Moon's orbit intersects the Earth's orbital plane relative to the Sun are called lunar nodes. At all other points in the lunar orbit, the Moon is above or below the plane in which the Earth orbits the Sun.

This is why a full moon does not always enter the Earth's shadow, as it will during a lunar eclipse, and the new moon does not always block the sun for those directly in the path of its small shadow, as it does during a solar eclipse. . The relative positions of the Sun, Earth, and Moon at one of the two nodes are aligned twice a year about 6 months apart to produce the conditions for at least some partial or total solar and lunar eclipses to occur in those portions of the planet. Earth positioned to observe them. As the 18.6-year cycle progresses, the positions of the nodes change so that the two times of the year during which eclipses can occur change for different times of the year.

Due to the relationship between the lunar orbit and the Earth's tilt, eclipses occur near the equinoxes during the major and minor lunar stops, although at opposite nodes. During an equalized lunar standstill, eclipses occur near the solstices. At the equator the moon rises at an angle more perpendicular to the horizon, and the angle between the maximum positions of its rise is not very wide. Towards the equator, the Moon can also pass directly overhead as it moves between the northern and southern maxima. The latitudes where this can happen are further north and south than those where the sun can do the same.

The moon rises at sharper angles relative to the horizon the further north or south a place on Earth is. In the northern hemisphere, the moon angles towards the south and in the southern hemisphere, towards the north. The change in the moonrise and moonset positions on the horizon becomes much more extreme. Beyond certain northern and southern latitudes, the extremes reach a point where, at one maximum, the Moon never crosses the horizon and at the other it never sets, but traces a great circle around the sky closer to the horizon or higher as you cross. the meridian but always visible.

How ancient cultures understood and related the patterns of the moon in the sky and on the horizon is a part of archaeoastronomy where there is still a lot of work to be done. In modern times we tend to give very little thought to the more apparent patterns of the moon in our daily lives and very few of us pay attention to the more complex long-term observations. Even without a complete understanding of the science and physics underlying these patterns, becoming aware of the observable physical realities of the sky as seen from the Earth's surface can help us appreciate the experience of these phenomena for ourselves.