The Moon: Orbital Dynamics, Phases, Eclipses, and Tides

The Moon is the Earth's only natural satellite.
It is located at an average distance of approximately $380,000\,km$ from our planet.

The Shared Face: We always see the same side of the Moon from Earth.
Explanation (Bound or Synchronous Rotation): This phenomenon occurs because the Moon has a "bound rotation" (gebonden rotatie). This means the time it takes for the Moon to rotate once around its own axis is exactly equal to the time it takes to complete one revolution around the Earth.
The Back Side: Because of this synchronization, the "back side" (achterkant) of the Moon is never visible from the Earth's surface.

Prevalence of Craters: The Moon's surface is covered in numerous craters caused by meteorite impacts.
Lack of Atmosphere: The primary reason for the high density of craters is that the Moon lacks a protective atmosphere.
Atmospheric Friction: On planets with atmospheres (like Earth), incoming space debris typically burns up due to friction with atmospheric gases. On the Moon, meteorites strike the surface at full speed without being hindered or incinerated.
The "Seas" of the Moon (Maria): Despite being dry, several large basaltic plains are named "Seas." Major named lunar seas include:
- Sea of Tranquility
- Sea of Serenity
- Sea of Crises
- Sea of Rains
- Ocean of Storms
- Sea of Fertility
- Sea of Nectar

Apparent Motion: Like the Sun, the Moon appears to rise in the east and set in the west daily. This is a "schijnbeweging" (apparent motion) caused by the rotation of the Earth on its axis.
Daily Delay: The Moon rises an average of $50\,minutes$ later each day and sets an average of $50\,minutes$ later than the previous day.
Cause of the Delay: This is due to the Moon's actual orbital revolution around the Earth. In a $24\,hour$ period, the Moon has moved a significant portion further along its orbit. Consequently, an observer on Earth must wait for the Earth to rotate a bit further to see the Moon from the same angle again.

Sidereal Month (Siderische maand): This is the time required for one full lunar revolution around the Earth relative to the fixed stars. It lasts exactly $27.3\,days$ . At the end of this period, the Moon occupies the same position in the sky relative to distant stars.
Synodic Month (Synodische maand): While the Moon orbits the Earth, the Earth is also moving in its own orbit around the Sun. To return to the same position relative to the Sun (completing a full cycle of phases), the Moon must travel for slightly more than two additional days. The synodic month lasts $29.5\,days$ .

Definition: The various appearances of the Moon as seen from Earth are called phases. They result from the changing relative positions of the Sun, Earth, and Moon.
Illumination: Only half of the Moon is ever illuminated by sunlight at any given time. The phases represent how much of that illuminated half is visible from an Earth-bound perspective.
The Cycle of Phases (Counter-clockwise direction):
- New Moon (Nieuwe maan): The illuminated side faces the Sun and away from Earth. The Moon is not visible from Earth on this day.
- Waxing Crescent (Wassende, sikkelvormige maan): A small sliver becomes visible as the Moon moves.
- First Quarter (Eerste kwartier): Exactly the right half of the Moon appears illuminated.
- Waxing Moon (Wassende maan): The visible illuminated portion continues to grow.
- Full Moon (Volle maan): The entire illuminated side faces the Earth. This occurs when the Earth is between the Sun and the Moon.
- Waning Moon (Krimpende maan): The illuminated portion visible from Earth begins to decrease.
- Last Quarter (Laatste kwartier): Only the left half of the Moon is visible.
- Waning Crescent (Krimpende, sikkelvormige maan): A final sliver is visible before returning to New Moon.

Orbital Inclination: Eclipses do not occur at every New or Full Moon because the Moon's orbital plane is tilted at an angle of $5^{\circ}$ relative to the ecliptic plane (the Earth's orbital plane around the Sun).
Syzygy Conditions: Solar or lunar eclipses can only occur when the Moon is at the intersection points of the lunar plane and the ecliptic plane (the nodes).
Lunar Eclipse (Maansverduistering):
- Occurs when the Earth is positioned directly between the Sun and the Moon.
- This can only happen during a Full Moon.
- The Earth blocks sunlight and casts its shadow over the Moon.
- Red Glow: During a total lunar eclipse, the Moon often appears red because Earth's atmosphere refracts (bends) sunlight into the shadow.
Solar Eclipse (Zonsverduistering):
- Occurs when the Moon is positioned between the Sun and the Earth, casting a shadow on Earth.
- This can only happen during a New Moon.
- Only a small portion of the Earth experiences the eclipse at one time.
- Umbra (Kernschaduw): The area of total shadow; observers here see a total solar eclipse.
- Penumbra (Bijschaduw): The area of partial shadow; observers here see a partial solar eclipse.

Date: Monday, August 21, 2017.
Location: Parts of the United States.
Path of Totality: A track approximately $115\,km$ wide stretched across states including Oregon (OR), Wyoming (WY), Nebraska (NE), Illinois (IL), Kentucky (KY), Tennessee (TN), and South Carolina (SC).
Maximum Duration: The longest duration of totality was observed at Goreville, Illinois, lasting $2\,minutes$ and $40\,seconds$ .
Mechanism: During this total eclipse, the Moon's umbra touched the Earth, and the solar disk was $100\%$ covered by the Moon.

Cause: Tides (ebb and flood) are caused by the gravitational forces of the Moon and the Sun, combined with the rotation of the Earth.
Flood / High Water (Vloed):
- Water on the side of the Earth facing the Moon is pulled toward it due to gravitational attraction.
- Simultaneously, water on the opposite side of the Earth also experiences high tide. This is caused by the centrifugal force (middelpuntvliedende kracht) resulting from the rotational movements of the Earth-Moon system.
Ebb / Low Water (Eb): This occurs twice a day when the water is pulled away from a specific location.
Spring Tide (Springtij):
- Occurs when the Sun, Moon, and Earth are aligned (during Full Moon or New Moon).
- The gravitational pulls of the Sun and Moon reinforce each other, leading to more extreme tides: higher high tides and lower low tides.
Neap Tide (Doodtij):
- Occurs during the First Quarter or Last Quarter.
- The Sun and Moon act at right angles to each other, partially canceling out their gravitational effects. This results in less extreme tides: lower high tides and higher low tides.