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The Moon
“The mind is not a vessel to be filled, but a fire to be kindled.”
—Plutarch
Viranga Perera, Ph.D.
Johns Hopkins University
Lecture Outline & Learning Objectives
Part 1: Moon Phases & Lunar CalendarIdentify phases, explain what causes phases & distinguish two
orbital periods of the Moon
Part 2: Moon’s Orbit, Water & EclipsesState average distance of the Moon, describe inclination of the
Moon’s orbit & explain what causes eclipses
Part 3: Tides, Farside of the Moon & Days Getting LongerIllustrate how tides work, explain why there is a farside & explain
why days are getting longer
Part 4: Formation of the MoonDescribe four main ideas of Moon formation
Part 1:Moon Phases & Lunar Calendar
Observing the Moon
Animation: NASA/GSFC
Images: NASA
A B C D E F G H
Phases of the Moon
C F G E A B H D
Images: NASA
A B C D E F G H
Images: NASA
1 2 3 4 5 6 7 8
Phases of the Moon
Images: NASA
New
Moon
Waxing
Crescent
First
Quarter
Waxing
Gibbous
Full
Moon
Waning
Gibbous
Last
Quarter
Waning
Crescent
1 2 3 4 5 6 7 8
Phases of the Moon
What causes phases of the Moon?
Ponder
Around between circa 610 to 546 BCE
First to consider a mechanical model
Thought Earth was a cylinder
Sun & Moon are seen through the holes
Moon’s hole changes shape
Anaximander of Miletus
Earth shown here as a sphere
Image: Dirk L. Couprie
Summer
Winter
Greek philosopher from modern day Turkey (around 500 BCE)
To Earth
Sun Moon
Fires sustained by
vapor from the Earth
Could explain Moon
phases & eclipses
Heraclitus of Ephesus
Animation: NASA/GSFC
Explanation
Religious Holidays
Art: Piero della Francesca
Easter (Christianity)
Image: balavenise
Ramadan (Islam)
Image: Subharnab Majumdar
Diwali (Hinduism) Vesak (Buddhism)
Image: Shehal
Image: Gilabrand
Rosh Hashanah (Judaism)
Image: Fanny Schertzer
Mid-Autumn Festival
Orbital Period
27.322 days (sidereal)
29.530 days (synodic) Not to scale
Earth
Moon
Sun
“Month”
Not to scale
Earth
Moon
Sun
“Month”
Orbital Period
27.322 days (sidereal)
29.530 days (synodic)
Image: NASA
Questions?
Part 2:Moon’s Orbit, Water & Eclipses
From the Earth to the Moon
De la terre à la lune
Jules Verne (1865)
Map: Henry Rogers
Baltimore Gun Club
“…it is clear that the aims of
that learned society were the
destruction of the human race
for philanthropical reasons
and the improvement of war
weapons, regarded as
instruments of civilization. It
was an assemblage of Angles
of Death who at the same time
were thoroughly decent men.”
Meeting on October 5th
“Many long years will go by
before our cannons again thunder
on a battlefield. We must accept
this fact and seek another outlet
for our restless energy.”
“I will lead you in the conquest of
the Moon, and its name will be
added to those of the thirty-six
states that form this great nation!”
Observatory of Cambridge
“The Moon is thus nearer to the Earth at
some times than at others, or in
astronomical terms, it is sometimes at
its apogee and sometimes at its perigee.
The difference between the two
distances is not negligible. At its apogee
the Moon is 247,552 miles from the
Earth, and at its perigee it is 218,657
miles away.”
Pretty close to modern values: 251,966
miles (apogee) & 225,744 miles (perigee)
The Moon’s
Orbit
Earth
Not to scale
Moon225,744 miles 251,966 miles
The Moon’s Orbit
Image: Melikamp
~240,000 miles
~30 Earth diameters
Laser RangingApollo 11 Retroreflectors
Images: NASA
NASA Goddard
Observatory of Cambridge“But in order for the Moon to rise to
the zenith of a given place the latitude
of the place must be no greater than
the Moon’s declination; that is, the
place must lie somewhere between
the equator and the twenty-eighth
parallel, either north or south.*
*Only between the equator and the twenty-
eighth parallel does the Moon reach the
zenith at its culmination. Beyond the
twenty-eighth parallel, it approaches the
zenith less and less as one moves toward
the pole.”
Florida
“It’s obvious that the same difficulties
will arise among the towns of
whichever state is chosen. The rivalry
will simply pass from the genus to
the species, from states to towns.
Texas has eleven towns that meet all
the necessary conditions. If Texas is
chosen, they’ll all fight for the honor
of having the project, and they’ll only
make more trouble for us. But Florida
has only one town, so I think our
choice is clear: Florida and Tampa!”
Orbit of the Moon
Image: Peter Sobchak
Water on
the Moon
Image:
NASA
Shackleton Crater
Located in the Moon’s
south pole
Diameter = 21 km (13 mi)
Depth = 4 km (2.5 mi)
Crater floor always in
shadow
Image: NASA/GSFC
Video: NASA/GSFC
Image:
Paige, D. et al. (2010)
Daytime Temperatures
Many permanently shadowed
regions are below 100 K
100 K = -279.67 °F = -173.15 °C
Water ice freezes:
273.15 K = 32 °F = 0 °C
What did people see?
Animation: NASA/GSFC
What causes eclipses?
Animation: NASA/GSFC
Explanation
Animation: NASA/GSFC
Explanation
Animation: NASA/GSFC
Explanation
From the Earth to the Moon
De la terre à la lune
Jules Verne (1865)
A Trip to the
Moon
Le Voyage
dans la Lune
Georges Méliès
1902
Apollo 11
Image: NASA
“This is the Commander of Apollo 11.
A hundred years ago, Jules Verne
wrote a book about a voyage to the
Moon. His spaceship, Columbia [sic],
took off from Florida and landed in
the Pacific Ocean after completing a
trip to the Moon. It seems appropriate
to us to share with you some of the
reflections of the crew as the
modern-day Columbia completes its
rendezvous with the planet Earth and
the same Pacific Ocean tomorrow.”
Image: NASA
Questions?
Part 3:Tides, Farside of the Moon &
Days Getting Longer
Tidal Force
Planet 1 Planet 2
Tidal Force
Water Planet
Rock Planet
“Super” Planet
Planet 2
Nearside of the Moon
Animation: NASA/GSFC
Tidal Locking
Day 1
Day 7
Day 15
Day 30 View above
Earth’s north pole
Earth
Nearside
Farside
The Moon’s Orbit
View above
Earth’s north pole
Earth
Moon
Earth
Ocean
Earth’s
24 Hour
Rotation
Boost
Slow
Rotation
The Moon’s Orbit
Image: Melikamp
~240,000 miles
~30 Earth diameters
The Moon
began
The Moon is moving away at 4 cm/year
Lengthening Earth’s day by 2 sec/100,000 years
Questions?
Image: NASA/ASU
Luna 3 (1959)
Image: OKB-1
LRO (Present)
Part 4:Formation of the Moon
Capture Model
IssueVery hard to make this work for a Moon-mass object
Earth
Moon
Co-Accretion Model
Image: NASA/JPL-Caltech IssuesWhy is the Moon significantly less dense?
Angular momentum of the system*
Fission Model
IssuesFeasibility of Earth spinning that fast
Earth day ≈ 3 hours!
George Darwin
Son of Charles Darwin Pickering (1907)
Image: ESO/L. Calçada
“Canonical” Giant Impact Model
Miki Nakajima
Questions?
Video: NASA/GSFC
Lecture Outline & Learning Objectives
Part 1: Moon Phases & Lunar CalendarIdentify phases, explain what causes phases & distinguish two
orbital periods of the Moon
Part 2: Moon’s Orbit, Water & EclipsesState average distance of the Moon, describe inclination of the
Moon’s orbit & explain what causes eclipses
Part 3: Tides, Farside of the Moon & Days Getting LongerIllustrate how tides work, explain why there is a farside & explain
why days are getting longer
Part 4: Formation of the MoonDescribe four main ideas of Moon formation
@virangaperera instantvirangavirangaperera virangaperera
Image: NASA/ASU
Viranga Perera, Ph.D.Johns Hopkins University
virangaperera.com
ourmoon.space
