1. Our Moon
• Earth’s only natural satellite
• One of approximately 185
moons in our solar system
• Officially named “Moon”,
however some literature calls
the moon Luna, the Latin word
for moon.
2. Giant-Impact Hypothesis
The Giant-Impact Hypothesis is the leading
hypothesis of how the moon formed and
suggests that the Moon formed from debris
left over from a giant collision between Earth
and an astronomical body about the size of
Mars about 4.5 billion years ago.
• The colliding body is sometimes referred to
Theia.
• Analysis of lunar rocks suggests that the
impact may have been a direct hit to Earth.
4. Supporting Evidence of the
Giant-Impact Hypothesis
• Earths’ spin and the moon’s orbit have
similar orientations
• Moon samples indicate the moon was once
molten
• The moon has a lower density than Earth
• Giant collisions are consistent with leading
theories of the formation of the Solar
System, 4.6 billion years ago
6. The Moving Moon
Only one side of the Moon is visible from
Earth because the moon rotates on its axis
at the same rate it orbits the Earth, every
27.3 days.
• The phenomenon is known as
synchronous rotation or tidal locking
• This causes us only to see the near side
of the moon.
• The side we can’t see from Earth is
called the far side of the moon.
7. Moon Stats
• Rotates and Revolves at the same rate, every
27.3 days
• Farthest to the Earth at apogee, about 405,400
km
• Closest to the Earth at perigee, about 362,600
km
8. The Moon’s Tilts
• The moon axial tilt is about 1.5o
, therefore
it does not have seasons.
• The moon’s orbital tilt as it revolves
around the Earth is 5o
9. Internal Structure
• Although the moon is less dense than
Earth, it is the second-densest moon in
the Solar System, after Io.
• Distinct crust, mantle, and core
FYI!
Moonquakes can occur on
the moon and astronomers
think they occur because of
tides on Earth, meteorite
impacts, or changes in
day/night temperatures.
10. Surface Geology – Mare
Maria (plural for mare) is
Latin for “seas”.
• Darkest parts of the moon
• Have smooth crater-free
surfaces
• They are low lying areas
filled with ancient basaltic
lava
• Almost all maria is on the
near side of the moon
11. Surface Geology – Highlands and Rilles
Highlands
• Light-colored
irregular hilly
regions made of
anorthosite
• Make up 84% of the
moon’s surface
• Contain mountains
up to 7,500 meters
tall
Rilles
• Trench-like valleys
• Resemble channels
Highlands
Rille
12. Surface Geology – Craters & Rays
• Craters are large
depressions caused
mostly by meteorite
impacts
• Surrounded by rays,
the trail of ejected
materials from the
impact of the
meteorite.
Crater
Rays
13. Lunar Atmosphere
The moon as no atmosphere
Without an atmosphere:
• The surface is unprotected from radiation,
meteorites, and solar wind.
• No sound can be heard on the moon
• Huge temperature variations -233 to +123o
C
• A cloud of moon dust called regolith
surrounds the moon created by small
particles from comets
14. Lunar Gravity
The gravity on the Moon is about 17% of what
it is on Earth.
• The surface gravity is about 1/6th
as powerful
as Earth’s or about 1.6 m/s2
• The gravitational pull is weaker because it is
far less massive than Earth.
• If you weighted 200 pounds on Earth, you
would weigh 34 pounds on the moon.
