Francisco M.
Pdillon
BSE Science 3
Astronomy
Part I. The Moon
1. Briefly explain the leading theory about how the Moon was formed.
The leading hypothesis for the Moon's formation is the Giant Impact
Hypothesis. According to this theory, a Mars-sized protoplanet (often referred to as
Theia) collided with the early Earth approximately 4.5 billion years ago. The immense
energy from the impact ejected a significant amount of Earth's mantle material into orbit,
which eventually coalesced under gravity to form the Moon. This theory is supported by
similarities in isotopic compositions between Earth's and Moon's rocks, as well as the
Moon's relatively small iron core compared to Earth.
2. What is meant by the Moon's "synchronous rotation," and how does it affect our view of
the Moon from Earth?
Synchronous rotation means the Moon takes the same amount of time to rotate on
its axis as it does to orbit the Earth, approximately 27.3 days. As a result, the same
hemisphere of the Moon always faces the Earth, while the far side (often misnamed the
"dark side") remains hidden from direct view. This is due to tidal locking, a gravitational
interaction that over time synchronized the Moon’s spin and orbit.
3. Describe two major types of features found on the Moon's surface.
The Moon's surface is dominated by two main types of geological features:
Maria - These are vast, dark basaltic plains formed by ancient volcanic eruptions. They are
less cratered and appear smoother, primarily on the side facing Earth.
Highlands- These are lighter, heavily cratered regions composed of anorthosite, older than
the maria. The highlands represent the Moon's original crust and are rich in impact features
from the early solar system.
4. How does tidal locking influence the relationship between the Earth and the Moon?
Tidal locking ensures that the same side of the Moon always faces Earth. This
phenomenon affects Earth-Moon interactions by creating predictable gravitational
effects, such as ocean tides. Tidal locking is a result of gravitational forces that over time
slowed the Moon’s rotation until it matched its orbital period. It also stabilizes the
Moon’s orientation and contributes to the long-term dynamical stability of Earth’s axial
tilt, which influences our climate.
5. List two ways the Moon affects Earth and explain its effects.
Tidal Forces: The Moon's gravity causes ocean tides on Earth, influencing marine
ecosystems, navigation, and coastal activity. The gravitational pull leads to bulges in Earth’s
oceans, creating high and low tides.
Axial Stability: The Moon stabilizes Earth's axial tilt, which helps maintain a relatively
stable climate. Without the Moon, Earth's tilt could vary more dramatically over time,
leading to extreme climatic shifts that could challenge the development and sustainability of
life.
Part II. The Moon Phases
1. What causes the different phases of the Moon as observed from Earth?
The Moon's phases are caused by the changing relative positions of the Moon,
Earth, and Sun. As the Moon orbits Earth, different portions of its sunlit half become
visible from Earth. These variations in visible illumination produce the cycle of lunar
phases—from new moon to full moon and back—over a synodic month of approximately
29.5 days.
2. List the eight primary phases of the Moon in order. Draw and describe each phase.
Phases Illustration Description
New Moon
The Moon is between Earth and the Sun; its
sunlit side faces away from Earth, making it
invisible to us.
Waxing
Crescent
A small, crescent-shaped sliver of the Moon
becomes visible on the right side.
Half of the Moon’s right side is illuminated; it
First Quarter
appears as a semicircle.
Waxing More than half of the Moon is illuminated, still
Gibbous increasing in light.
The entire face of the Moon is illuminated as
Full Moon
Earth is between the Moon and the Sun.
Waning The light begins to decrease, with more than
Gibbous half of the Moon still visible.
Last Quarter The left half of the Moon is illuminated.
Waning Only a thin crescent is visible on the left side,
Crescent decreasing until the New Moon phase.
3. Differentiate between waxing and waning phases of the Moon.
"Waning" refers to the phases during which the illuminated portion of the Moon visible
from Earth is decreasing, transitioning from full moon to new moon. "Waxing" describes the
opposite—when the visible portion is increasing, from new moon to full moon. Waxing
phases are seen on the right side in the Northern Hemisphere, while waning phases appear on
the left.
4. Why don’t eclipses occur every month despite the regular phases of the Moon?
Eclipses are infrequent because the Moon's orbit is tilted about 5 degrees relative to
Earth's orbital plane (the ecliptic). This means the Moon usually passes slightly above or
below the Sun from our perspective during new or full moons, preventing alignment.
Eclipses only occur when the Sun, Earth, and Moon align closely along the ecliptic—this
alignment happens only during specific periods called eclipse seasons.
