The MOON Kansas State Teachers College
THE KANSAS SCHOOL NATURAL/ST Emporia, Kansas
Vol. 17
No. 2
DECEMBER
1970
The Kansas
School Naturalist
Published by
The Kansas State Teachers College of Emporia
Prepared and Issued by The Department of Biology, with the cooperation of the Division of Education Editor: Robert J. Boles
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3
The MOO N
by DeWayne Backhus
The Moon's Positio n ill Space
The Earth's moon is possibly one of the
very few places within the solar system where
the events of cosmic time are recorded. From
Earth one can see the face of the " man in the
moon" but never the back of his head. A lunar
month is 27.3 or 29.5 days. A person on the moon
should be able to jump from a very high cliff
without harm. The moon would be an ideal
place for an observational astronomer.
All of the previous are true statements
concerning planet Earth's only natural
satellite-the moon. Some of these statements,
al though true, may sound strange to the reader
who is accustomed to living on an object in
space with a different set of characteristics.
This issue of The Kansas School Naturalist will
be devoted to a discussion of the features of the
moon which prompt statements such as appear
in the first paragraph , and which have
prompted man on Earth to set foot on the
moon.
Since ancient times man has been able to
observe the moon proceed through its monthly
performance. Because of the spatial
relationship between our sun, Earth, and moon,
we observe a cyclic change of position and
appearance. This cyclic pattern of events
which the moon undergoes is our basis for the
month as a unit of time. Let us use the
accompanying diagram, Figure 1, to discuss
the relationship of the sun, moon , and Earth.
We on planet Earth see all celestial objects
in our solar system-the solar system being
comprised of the sun , the nine planets, thirty­
two moons, thousands of asteroids, a number of
comets, and millions of meteoroids-with the
exception of the sun, as a result of light energy
emitted from the sun being reflected by the
celestial objects. Since all bodies are nearly
spherical in shape, at any time one hemisphere
of the celestial body will be illuminated ( the
hemisphere toward the sun). This is indicated
by the dark and light shading of moon and
Earth in the diagram. The Earth spinning
(rotating)' on its axis once every twenty-four
hours with respect to the sun enables the Earth
inhabitant to experience hours of daylight and
darkness. When the moon is at position A, the
Earth observer sees the "dark side" of the
moon. No light reflected from the moon will
reach us. Furthermore, the moon is in the
same direction in space as the sun and the sun 's
light overwhelms any light which might be
reflected toward us, thus, we cannot generally
"see" the moon and we say that the moon is in
the new phase, If we could see it. it would
"appear" as in Figure 2, A'. Because the moon
revolves' about the earth counterclockwise, we
on Earth begin to see some of the moon's
surface which is receiving light from the sun.
The moon appears as a thin crescent such as is
seen in Figure 2, B'. This phase from A' to C' is
referred to as the waxing crescent phase.
About seven days after the moon is at position
A, it will have passed gradually through
position B and will be at C. As we view the
moon from Earth, it appears as in Figure 2, C',
and we speak of a first quarter moon. As the
moon progresses from position C to D (Figure
1), we see more of its surface reflecting light
and we speak of the waxing gibbous phase, D'.
About fourteen days after new moon , the moon
is opposite the sun in space , position E, and we
see the entire moon 's disk illuminated as in E ' .
We speak of the full moon. And similarly, as
the moon revolves around the Earth, it passes
through the waning gibbous (F and F') , third or
last quarter (G and G'), waning crescent
(H and H' ), and back to the new moon. Thus,
the moon's cycle of phases throughout the
course of 29.5 days enables us to observe it as
an almost dark disc at new moon to an entire
disc reflecting light at the full moon phase .
The Apollo Project personnel have relied
upon the relationship between the sun, Earth,
and moon for the manned moon landings. All
'Rotation refers to the motion of a body about a point or line through that body. Revolution refers to the motion of a body about some pOint outside of that body. 4
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Direction of
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SUN
h
b
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e
()a
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Figure 1. The sun, Earth , and moon positions A through H are shown . The diagram is not to
scale with respect to size of bodies or distance between bodies. The sketch is that which one
located in space looking down onto the solar system would observe .
New Moon
Age: 0 . 0 day
B'
Waxing Crescent
Age' 5 . 0 days
E'
Full Moon
Age: 15.0 days
F'
Waning Gibbous
Agel 19.0 days
A'
C'
First Quarter
Age I
7.1 days
G'
Third Quarter
Age' 21.4 day.
D'
l,;aring Gibbous
Age: 11.1 days
H'
Waning Crescent
Age: 23.5 days
Figure 2. Photographs showing the moon's appearance for each phase. The letters A' through
H' on the photographs correspond to the moon positions A through H shown in Figure 1. (The new
moon, with no light reflected from it is difficult to observe since the moon is above the horizon
with the sun. A' is therefore a sketch, not a photograph of the moon).
5
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Figure 3. A top-view sketch of the sun, Earth (at EI and E 2 ), and the moon at MI ,M 2, and M3.
Since the star is very far away, the line of sight to the moon and the star at Earth position EI is
parallel to the line of sight to M2 and the star from Earth position E 2·
landings were planned for the moon near first
quarter phase. Thus, an astronaut could be on
the Earth-side of the moon near the
terminator-the boundary between light and
dark on the moon. Since the temperature of the
lighted portion of the moon rises to + 240
degrees F; and since the temperature in the
dark portion drops to -240 degrees F ; the
astronauts were able to capitalize upon this
area of " moderate" temperatures for their
extra-vehicular activities on the lunar surface.
A person may also use Figure 1 to understand
how the time of moonrise changes as the moon
goes through its cycle of phases. Since the sun
and moon are in the same direction in space at
new moon phase, and since the sun and moon
appear to rise and set due to the rotation of the
Earth, we would expect the new moon to rise
about the same time as the sun rises. This
occurs when the observer on the rota ting Earth
is located near position a. When the moon is at
position 8 , the Earth observer located at b
would see the waxing crescent moon at 8 rise .
Similarly, a tangent line drawn to the Earth
from any moon phase position indicates the
position and time of day on Earth for the time
of moonrise or moonset. For example , when
the moon is at the full phase (E) , tangent lines
drawn from the moon to Earth would touch the
Earth at e and a. Since the Earth rotates on its
axis counterclockwise; the moon would rise
for the observer at position e on Earth (about 6
PM or sunset) and set for the observer at
position a on Earth (about 6 AM or sunrise.). If
you recall that the Earth rotates on its axis, the
observer at e will be at position a after twel ve
hours of time. Table I summarizes the time of
moonrise and moonset for the various phases.
The reader is asked to observe and verify the
fact that the full moon rises in the east about
the same time that the sun sets in the west, as
well as the other approximate times of
moonrise indicated in Table I.
The time for the moon to make one
complete revolution about Earth is dependent
upon the reference object that we use for
measuring the period of revolution. Either the
sun or a reference star may be used to
determine this period of lunar revolution. If the
sun is used as the reference object, the moon
completes its revolution in 29.5 days-this is
called the moon's synodic period. If the moon's
revolution is measured using a star for
reference, the period of revolution is 27.3
days- the sidereal period of the moon. The
difference in period is a consequence of the
distance to the reference objects. Using Figure
3 assume that the moon is at MI ' Note the
direction in space of the moon and the star. The
moon, moving counterclockwise in its orbit,
completes one revolution with respect to the
star in 655 h 43 m , or 27 .3 days. The moon 's
6
TABLE I. TIME OF MOONRISE·
Phase
New
Position in Appearance,
Figule 2
Figure 1
A
A'
Time of Moonrise
6A M
Position of observer on
Earth in Figure 1
a
Waxing Crescent
B
B'
Between 6 AM and 12 noon
Vicinity of b
First Quarter
C
C'
12 noon
c
Waxing Gibbous
D
D'
Between 12 noon and 6 PM
Vicinity of d Full
E
E'
6PM
e
Waning Gibbous
F
F'
Between 6 PM and midnight
Vicinity of f Third (Last) Quarter
G
G'
12 midnight
g
Waning Crescent
H
H'
Between 12 midnight and 6 AM
Vicini ty of h
'The time of moonrise is simplified ; times of sunrise and sunse t are assumed to be 6 AM and 6 PM
respectively. Thu s, some adjustment in times of rise (a nd set) will have to be made with the
seasona l variations of Earth .
position at the end of thi s time interval is
s hown at M2 : the Earth is at E 2 . But the moon
has not com pleted one full revolution with
respect to the sun. Because the su n is close r:
and because the Earth revolving about the sun
carries the moon with it , the moon will need
another 2.2 days to complete its cycle with
respect to the sun or arrive at M3 . This period
of revolution of the moon with respect to the
sun, the synodic period, requires 29.5 da ys.
Thus, the synodic period is the time interval
between the successive same phase of the
moon, that is , the time from one new moon to
the next, or from full moon to the next full
moon , etc.
We can always see the face of the ·' man in
the moon" but never the back of his head .
Stated another way. the moon always keeps its
sa me side or hemisphere toward the Earth.
Thus, no Earth observer has ever see n the
"far-side· ' or other hemisphere of the moon.
Man ' s first photographs of the far-side of the
moon ca me as a result of the Soviet Union's
Luna 3 efforts on October 7, 1959. Since then
bc ·': the Soviet Union and the United States
h2 ..: mapped the far-side in some detail. The
Apollo 8 crew ( Borman, Lovell, and Anders)
were the firs t men to directly observe the
"backside" of the moon.
The fact that we cannot see the far-side of
the moon is a consequence of the moon 's period
of rotation and revolution. The moon completes
one rotation on its axis in the sa me length of
time as it completes one revolution about
Earth. The sidereal period of revolution should
be considered as the moon 's period of
revolution. Us ing Figure 1, moon position A.
imagine an object or lunar feature on the
surfa ce of the moon's dark side . and in the
cente r of the hemisphere of the moon toward
Earth . As the moon revolves 90° about Earth
from A to C, the moon also r ota tes 90°
cou ntercloc kw ise on its axis. Thus , the object
which was imagined on the moon at A will still
be in the center of the hemisphere of the moon
toward Earth. Because the period of revolution
is equal to the period of rotation , we see the
face of the " man in the moon .' · but nev er the
back of his head.
The day for the moon inhabitant would be
equal to 29 .5 Earth days. or the lunar day is
equal to the moon's synodic period of
revolution. This long day is of particular
interest to the potential observational
astronomer contemplating an observatory on
the moon. If the astronomer had an
observatory located on the moon's equator, he
would be able to view all regions of the s ky
7
rather leisurely during this long lunar day . Of
course , he would have to overcome some other
rather difficult problems since he would be
experiencing a "noon" temperature of about
+ 240 degrees F.
Another phenomenon whi ch we experience
on Earth as a consequence of the spatial
relations hips of the sun, planet Earth. and the
moon . is eclipses. Since the moon orbits about
the Earth . the possibility exists for the moon to
block (eclipse) the sun's energy bound for the
Earth when the moon is at its new pha se (refer
to previous Figures); or Earth may cast its
shadow on the moon when the moon is full.
When the moon passes between Sun and Earth ,
block ing the light from the sun. we experience
a solar eclipse ; and when the Earth blocks the
sun's light bound for the moon , a lunar eclipse
will occur. We shall look at eclipse phenomena
in some detail.
An understanding of eclipses requires
some knowledge of shadow phenomena. Since
the sun is the only intrinsic source of light in
the solar sys tem (all other bodies are seen as a
result of their reflected light). these " cold"
bodies will cast a shadow in space on their side
opposite the sun. As Figure 9 shows. the
shadow has two regions-a dark region
receiving no light from the sun, the umbra , and
a lighter region relative to the umbra. the
penumbra.
The extent of the umbra and penumbra
depend upon the size of the sun and the "cold
body ," and the distance between them .
Let us now consider the sun , Earth , and
moon system. The moon 's orbit about the
Earth is not circular, it is elliptical. (See
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Figure 4. Elements of the moon's elliptical
orbit about planet Earth. The distance from
perigee to apogee is about 476,000 miles.
Figure 4.) The Earth is located at one focus of
the ellipse. Thus, the Earth-moon distance is
variable. When the moon is at perigee , closest
to the Earth , it is 220,000 miles away; and when
the moon is at apogee , farthest from the
Earth in its orbit, it is 252,00() miles away. The
moon 's average di stance from the Earth is
238,000 miles. Even though the average
distance of 238,000 miles is appropriate for
most discussions of lunar phenomena , the
variable distance to the moon is essential for a
discussion of solar eclipses.
F igu re 5 shows the moon at the new phase,
the Earth, and sun. The moon 's umbra extends
into space 232,000 miles from the Earth .
Assume that the moon is nearer than average
to the Earth I at or near perigee )-about 220,000
to 230 ,000 miles from Earth . The moon 's umbra
will extend to the Earth, or the Earth will fall
lnto the umbral region of the moon's shadow.
The Earth observer in the umbral region of the
shadow will not be able to see any of the
sun-hence, a total solar eclipse would be
experienced by this observer. The shadow
region on the Earth during a total solar eclipse
is a maximum of 167 miles wide; and beca use
the moon revolves in its orbit cou nterclockwise
(from west to east as observed from Earth) at
a rate of 200,000 miles per hour, the period of
totality will last only a maximum of seven
minutes.
The observer on the Earth in the penumbra
of the moon's shadow will experience a partial
lunar eclipse. Because of the greater extent of
the penumbra this type of solar eclipse is more
commonly experienced. During a partial solar
eclipse , only a partial dimming of light
intensity may be observed, such as on a partly
cloudy day . In fact , most people are totally
unaware of partial solar eclipses unless
forewarned to observe. (CAUTION: Never look
directly at the sun ; view it only by indirect
methods of projection or with a properly
equipped telescope . See Science and Children ,
January/ February, 1970; or The Science
Teacher, February, 1970.)
If the Earth and moon are farther apart
than 232,000 miles , when the moon is at or
approaching apogee, the Earth will lie in the
umbral extension of the moon 's shadow. Lines
of sight drawn as in Figure 6 show that the
8
EARTH
Figure 5. The spatial relationship of the new moon, Earth, and sun producing a total solar
eclipse . The moon-Earth distance is assumed to be closer than average. What is shown in two
dimensions on the diagram is in reality three dimensional. (Sizes and distances are not to scale ).
Earth observer will be able to see the outer
ring of the sun, with the moon superimposed on
the sun's central region. This type of solar
eclipse is referred to as an annular lunar
eclipse. (The designation , annular, is not to
suggest an annular occurrence, but refers to
the ring, or annulus, of light seen around the
superimposed moon. )
Thus, the occurrence of a solar eclipse is a
consequence of the moon passing between the
Earth and sun-the moon must be at its new
phase. Whether the solar eclipse is total ,
partial, or annular depends upon the moon­
Earth distance and the particular shadow
region in which the observer is located.
But a solar eclipse does not occur every
29.5 days , even though a new moon occurs at
this interval. Why ? Another condition must be
satisfied before solar eclipses may occur. The
Earth revolving about the sun defines a plane,
the plane of the ecliptic. The moon 's plane of
revolution is inclined at an angle of 5 0 9' (five
degrees , nine minutes) to Earth's plane of
revolution about the sun . In Figure 7 an edge
view of the moon's plane of revolution about
the Earth and the plane of the ecliptic is shown.
Two planes intersect to define a line . The line
of intersection of the plane of the ecliptic and
the moon 's plane of revolution about the Earth
is called the line of nodes. See Figure 8. The
sun, Earth , and moon must all lie on or near
this line of intersection , the line of node s, and
the moon must be in the new phase before a
solar eclipse will occur. Also, the Earth
observer must be strategically located in order
to experience the eclipse, should the necessary
conditions be existent. Furthermore, if it is
cloudy, all preparations for observing the
spectacle may be for naught.
The circumstances of a lunar eclipse are
not so complicated as those for solar eclipses.
In Figure 9 the sun , Earth, and moon are again
shown. The moon is near the full moon phase.
The tip of Earth's umbra is cast into space
860,000 miles from Earth on the average. But
the maximum distance of moon from the Earth
is only 252,000 miles. Thus , the full moon is
always well within the Earth's umbra, if the
line of nodes condition is fulfilled .
When the moon is in Earth's penumbra, a
partial lunar eclipse will occur. If the moon
passes through the umbra , then we on Earth
might observe a total lunar eclipse. There is no
lunar equivalent to the annular solar eclipse .
All persons on the night side of the earth
can observe the lunar eclipses . Also , since the
Earth 's shadow is so large, the duration of a
lunar eclipse is much greater than a solar
eclipse , unless the moon just passes through
the edge of Earth's shadow. Thus, most people
have experienced more lunar eclipses than
solar eclipses .
Going to the Moon
The moon has raised many questions for
man to ponder-How far away is it? What is its
composition? Does it support life? (What is
life?) How did it originate ? etc. Some questions
about the moon could be answered from Earth .
Others could not. If a person weren't motivated
to " get there" for scientific reasons, possibly
he would be motivated solely by his dream and
de sire to "get there" because it exists .
Figure6. The geometry of an annular solar eclipse. The moon must be at a greater distance
from the Earth than the distance the umbra of the moon extends into space.
Which ever may be the case, man's dream
began to approach connotations of reality fifty
years ago. The February, 1920, issue of
Scientific American contained the following
quote:
" The public was startled recently by
newspaper announcements that a rocket
had been invented which would carry as
far as the moon. Sensational as thi s
statement appeared to be, it was
nevertheless issued by the Smithsonian
Institution and was based on the work of
Dr. Robert H. Goddard of Clark
University, who has been conducting a
long series of experiments on existing
forms of rockets. He has developed a
method of increasing the efficiency of
this type of projectile to such an extent
that it will be possible to propel a rocket
beyond the influence of the Earth. "
(Scientific American, Feb ., 1920 )
This announcement would seem incredible to a
public which had known of the airplane and
automobile for less than twenty years.
The United States officially inaugurated
the Space Age in 1958 when it sent its first
artificial satellite , Explorer I, aloft into Earth
orbit on January 31. As the U.S. space program
developed, more than thirty-five major space
projects were undertaken. Those projects
range from launching communication satellites
about Earth to manned space projects.
Undoubtedly, the Apollo project has
attracted the most attention. Apollo, relying
upon the pioneer work of Mercury and Gemini ,
was initiated ( 1) to land American explorers on
the moon and bring them back safely to Earth ,
(2) to establish the technology required to meet
other National interests in space, and (3) "to
achieve for United States pre-eminence in
space."
Project Apollo, in addition to its reliance
upon the base provided by earlier manned
projects (Mercury and Gemini) , also relied
upon the data gathered through three
unmanned lunar exploration projects : Ranger ,
Lunar Orbiter, and Surveyor. We shall look at
each project to see how it contributed to the
success of Apollo.
If man were going to successfully land on
the moon, explore, and return to Earth, then he
must have some knowledge of the terrain. The
best terrestrial telescopes resolve objects only
800 feet or greater in diameter. Thus, a series
of unmanned projects were initiated simply to
photograph the lunar surface.
The Ranger project was initiated in 1961 to
photograph the lunar surface prior to hard­
landing (crash-landing) on the moon. These
photographs were transmitted to Earth as the
Ranger approached its hard-landing site. The
photographs were able to resolve objects with a
diameter as small as ten inches .
The Ranger photographs were restricted to
a very local area of hard-landing ; hence, a
project was initiated to photograph a broader
area (20 degrees of latitude near the lunar
equator). The Lunar Orbiter series which
began in 1966 was designed to take high­
resolution, close-range photographs of the
equatorial region of the moon. These
photographs provided the basis for the
selection of landing sites for the Apollo lunar
landings.
10
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SUN
/
Plane of Ecliptic
~
5"9'
Moon's Plane of Revolution
Figure 7. An edge view of the plane of the ecliptic, the Earth's planeof revolution around the
sun, and the moon's plane of revolution around the Earth are shown. The angle between the two
planes is 5°,9'.
During the mid-sixties a controversy was
raging concerning the nature of the lunar
su rface. On the basis of experiments on Earth
involving radiation of terrestrial materials,
some scientists concluded that the lunar
surface, which is constantly being bombarded
by solar radiation, was possibly covered by a
" dusty" layer. It was thought that this layer of
dust might be sufficiently thick and of such low
density that a craft landing on the moon could
not be supported. To test this hypothesi s, the
surveyor project was initiated to determine if
the lunar surface could support a spacecraft
landing on its surface.
As a result of the Surveyor's soft-landing
on the moon, it was concluded that the moon
was covered by only a su perficial layer of dust
(radiation-damaged material ) and that the
lunar surface could support a manned landing
craft. In addition to its soft-landing capability,
the Surveyor was designed and equipped to
photograph its landing vicinity and perform
experiments on the lunar surface. The
photographic resolution of the Surveyor 's
camera was .02 of an inch, greatly extending
man's knowledge concerning the nature of the
lunar surface. The Surveyor VII spacecraft
also carried with it instruments which let
scientists tentatively conclude that the lunar
surface had a basa lt-like composition.
As the unmanned lunar exploration
projects were being developed, manned
projects were also being developed. The
Mercury program first placed an American
astronaut, Alan Shephard, into a suborbital
flight on May 5, 1961. As part of the same
program, John Glenn became the first U.S.
astronaut to orbit the Earth on February 20,
1962. The objectives of Mercury were entirely
experimental in nature . Mercury was intended
simply to pioneer the technology for manned
space flights and determine man' s capability
for space flight.
Al so experimental in nature was the
Gemini project of 1965 and 1966. Deriving its
name from the constellation Gemini-marked
by the twin stars Castor and Pollux-the two­
manned space flights of Gemini were intended
to determine man's capability for prolonged
space flights of up to two week s duration. Also,
the Gemini projec t involved space
rendezvous-a technique to be used by Apollo
(invol ving the command module and the lunar
module) for economi zing on fuel for a lunar
landing. The Gemini astronauts also performed
" space walks" or extravehicular activity to
determine man's capabilities in a low-gravity
environment.
I n addition to successfully pioneering the
technology necessary for manned space flight ,
Gemini provided man with some very
enlightening photographs of Earth from an
altitude of one-hundred miles. Patterns of
atmospheric and oceanic circulation aided the
meteorologist seeking a basis for more
accurate weather predictions; vegetation
observed gave man clues for planning for the
food needs of a growing popUlation; certain
large-scale geologic features were observed;
but perhaps most important was a new
perspective of Earth " as one" provided by
these high altitude photographs. More will be
said of this latter point following the discussion
of the Apollo project.
As stated previously, the objectives of the
Apollo Program were threefold: (1) to land on
the moon and return; (2) to establish the
technology necessary for future space efforts,
and (3) to gain pre-eminence for the United
States in space exploration. Unlike the goals of
11
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Figure 8., The plane of the ecliptic and the moon's plane of revolution are shown in three
dimensions. The line formed by the intersection of the plane of the ecliptic and the moon's plane of
revolution is called the line of nodes. If Earth, moon, and sun are oriented as shown at A, a solar
eclipse of some type will occur.
Mercury and Gemini, which were
experimental in nature, the goals of Apollo
were operational . As the reader already knows.
the objectives of Apollo have been met.
Let us recount some of the highlights of the
Apollo project to date . All Americans perhaps
wondered whether the Apollo objectives would
ever be achieved in January , 1967. As Apollo 2
was being prepared for launching, and as the
three astronauts made final preparations in the
command module, a defect in the wiring
resulted in the fire which cost the lives of the
three astronauts. Following much frustration
and speculation, changes were made in terms
of the atmosphere of the module and the desigr.
of the module 'S hatch (or door ). The 100 per
cent oxygen environment was dropped in fa\'or
of a nitrogen-oxygen atmosphere. The hat ch.
which had been designed to open inward La
prevent opening in space because of the
differential pressure within the module and lhe
" vacuum" of space, was redesigned to o;Jen
outward to enhance escape if necessa ry p~lQ r
to launch . But the interes t of the public :::
Apol'lo wa s renewed in December. 1968 when
Astronauts Borman, Lovell , and Anders
became the first men to go entirely beyond the
Earth's gravitational pull and insert their
spacecraft into orbit around the moon . Ap ollo 9
followed in February of 1969. Astronauts
:\lcDivitt, Scott, and Schwichart orbited the
Earth to make final systems checks on their
lunar module , and they performed rendezvous
maneuvers with their command module and
the lunar module. The Apollo 8 crew had not
had the lunar module on their December trip to
the moon , hence the Apollo 9 flight was a
necessary preliminary to flights with the lunar
module to the moon. In May, 1969 , the Apollo 10
spacecraft carried Astronauts Stafford . Young ,
and Cernan to the moon for a final rehearsal
prior to the subsequent Apollo II landing on the
moon. The Apollo 10 project involved
separation of the command and lunar modules
to allow the lunar module to fly within ten
rr:iles of the lunar surface prior to rendezvous
wi t h the command module and return to Earth.
It was this close encounter of the Apollo 10
12
SUN
Figure 9. The geometry of a lunar eclipse. The moon must pass through Earth's shadow for a
lunar eclipse to occur. (Distances and sizes are not drawn to the same scale).
lunar module with the moon which resulted in
detection of local concentrations of mass near
the lunar surface. Mapping of these mascons
resulted in complete lunar orbit recalculations
and changes in lunar module fuel supply
necessary to land the Apollo lliunar module on
the predetermined landing site in the Sea of
Tranquility.
Then on July 16, 1969, Apollo 11 climaxed
the Apollo program with footsteps on the moon .
As Astronaut Collins maintained vigil in the
command module , Astronauts Neil Armstrong
and " Buzz" Aldrin , in that order , became the
first men from Earth to step onto the lunar
surface. In addition to achieving the basic goals
of Apollo as previously defined , direct
scientific investigation of the lunar surface had
begun. A seismometer was set up to determine
the occurrence and nature of lunar quakes , and
hence moon internal structure ; a solar panel
was placed to record particle emissions from
the sun possibly arriving at the lunar s urface; a
reflector was established for locating the exact
landing site and to reflect a laser beam to be
transmitted from Earth for accurate
measurement of the Earth-moon distance; and
valuable samples of the lunar surface were
gathered for return and analysis on Earth.
In November, 1969, the Apollo 12 mission
again placed man on the moon. Astronauts
Bean and Gordon performed more elaborate
scientific investigations. Another seismometer
was placed for detecting natural lunar
dis turbances, a magnetometer for measuring
the moon' s gravitational field , and
spectrometers and ion detectors to provide
more explicit data on the lunar atmosphere and
particles arriving at the lunar surface from the
sun.
The capability of man to coordinate many
systems and monitor his environment was
revealed by the near tragic flight of Apollo 13.
When some unknown malfunction caused the
oxygen tank of the command module to
rupture , the astronauts of Apollo 13 had to rely
upon reserve capabilities of the "frail " lunar
module for their return to Earth . From the
standpoint of making new decisions and
coordinating many systems in a crisis
situation, Apollo 13 wa s possibly the most
s uccessful of all Apollo flights. Certainly,
futur e lunar exploration will continue , but the
general public has experienced the peak of
excitement with respect t~ lunar exploration.
Lunar History and Processes
To the Earth observer the moon is the
second brightest object in the sky-second only
to the sun. This is not because the moon is so
large-it is a small celestial body-but because
13
the moon is so close to Earth. Its angular
diameter is about one-half degree of arc . (This
angular size varies since the moon 's orbital
path about the earth is not circular, but
elliptical. You can verify that the moon 's
angular size varies with its distance from
Earth by carefully measuring the diameters of
the moon in Figure 2. ) If we know the moon's
distance from Earth , which is on the average
238 ,000 miles, then we can calculate its
absolute or actual diameter in miles. The
calculation gives an absolute diameter of 2,160
miles.
If you look at the moon with the naked eye ,
binoculars, or a telescope , you will get some
impressions of the nature of the lunar surface.
The moon 's surface has " dark-colored" areas
and "light-colored" regions . If a magnifying
instrument (binoculars or a telescope ) is used ,
one can see that the dark-colored areas are
relatively smooth and the light-colored regions
are rougher . However, the contrast observed of
the lunar surface depends upon the sun angle or
the particular moon phase observed. (Note
Figure 2; look at the same lunar feature on a
number of different photographs.)
The smooth, dark-colored regions are
called the lunar maria , or seas. The rougher ,
light-colored regions are referred to as the
highlands or continental regions of the moon. A
binocular or telescope also reveals that there
are a greater number of craters on the lunar
highlands , and very few in the mare region.
Thus, very few craters have been formed on
the lunar surface since the formation of the
maria. This simple observation is actually a
powerful clue to lunar history. Since there is no
appreciable atmosphere on the moon , hence
little weathering or erosion as we know it, the
events of cosmic time are recorded on the
lunar surface. Man has assumed the task of
studying the moon's surface directly in as
much detail as possible.
The Apollo 11 crew brought back to Earth
about 50 pounds of lunar samples from the Sea
of Tranquility-a mare region. The landing site
was about 80 miles from a lunar highland. The
lunar samples could be classified into three
basic categories: (1 ) meteorite fragments , (2)
surface rocks in a fairly good state of
preservation , and (3) badly damaged
(" weathered ") surface material as a result of
radiation damage and meteorite impact.
Meteorite fragments , or fragments which
resemble meteorites found on Earth, would be
consistent with the theory that the lun ar
craters formed as a result of meteorite impac t
throughout the life history of the moon. Recall
that the greatest density of craters is seen on
the lunar highland region. What does this
mean?
The surface rock in a reasonabl y good state
of preservation included two basic groups:
those similar to terrestrial basalts, a dark ,
fine-grained, iron-magnesium rich silicate
rock; and those similar to anorthosites found
on Earth, a coarse-grained igneous rock
composed primarily of plagioclase feldspars.
The two basic kinds of rocks differ from
each other in appearance , density,
composition , and age. The basalts, which were
found in greater abundance , are believed to
represent mare material. Radioactive age
dating techniques indicated an age of about 3.5
billion years for the basalts , or mare material.
The anorthosites, found in less abundance,
were dated to be 4.5 billion years old . They are
believed to represent the rock composition of
the highland region .
The ages of these two fundamental rock
types are significant. Evidently the continental
or highland regions were formed early in the
moon's history, hence their age of 4.5 billion
years. These data also agree with the age of 4.5
billion years assigned to some terrestrial
meteorites and the planet Earth as a whole .
Also, early in its history the moon was (?)
bombarded with many meteorites , producing a
highly cratered lunar surface . This high
frequency of lunar cratering is also consistent
with contemporary theories of formation of the
solar system from a large mass of gas and
particulate matter.
The mare basalts revealed an age of 3.5
billion years. Evidently a billion years after the
occurrence of the highlands either internal
forces or external forces triggered the
processes which produced the lunar maria.
Consistent age dates of the Apollo 12 samples
from Oceanus Procellarum support the
speculation that ail lunar maria formed at
about the same time . Since the formation of the
14
maria , the frequency of m e teorite impa ct ha s
not been nearly so g reat a in the first billion
years of the his tory of the moon.
There are still m a ny una nswered que stion s
con ce rni ng the m oon ·s his torv and the hi s tory
of our solar system . In fact today only few
ques tions have bee n an swered . many mo re
ques tions have been raised by the scientists
studying lun ar mater ials , processes. and
history . Did the maria form as a re sult of
internal forces on the moon. indicati ng that the
lunar in te rior is hot and active? Or were the
maria formed as a result of external
forces- su c h as meteorite impact and
subsequent shock melting? Similarly, are
craters formed from meteorite impact or are
they the result of volcanic ac tivity s imilar to
volcanic activity witne ssed on Earth ? What
events formed the" ra y " sys tem of such young
craters as Copernicus, Tycho, and Kepler ? Are
these ray systems the result of fi ssure or flank
volcanic eruptions or are ray sys tems produced
by ejecta or debri s thrown out during meteorite
impact ?
The "hot" moon theories and " cold " moon
theories will be accepted or rejected .
depending upon which is consistent with
observational data obtained by a direct stud y of
the moon. The possibility also exists that the
moon was a warm and active body during its
first billion years of exis tence, and during the
last 3.5 billion years it has been a cold body
with external forces shaping its surface. Thu s.
more questions have been rai sed about the
moon since the Apollo landings than have bee n
answered.
The Moon, Man, and the Future
Certainl y man 's exploration of the moon
has just begun. Future scie ntific exploration
efforts will be made to provide us insights for
the solutions to some of the que stions raised
earlier. In the meantime it is interesting to
speculate concerning how man might make
responsible use of the moon.
A number of preposterous suggestions have
already been made. Suggestions have been
made that high pollution industries be placed
on the moon : that the moon's surface be
covered with a reflecting dust to increase the
amount of light reflected to Earth , thus acting
as a de terrent to crime; and that the moon be
made a universa l exile or refuge from Earth .
These , however. are not rea sonable, especially
the one v\'hich would upset the balance of
nature on Ea rth .
I be lieve that man 's future ventures on the
mo on will capitalize upon the unique
environment which the moon possesse s. Thus,
the moor. will not provide a place for
competit ion with usual Earth activities, but it
will com plement Earth with respect to a
number of activities which are not carried out
effectivelv in Earth's environment. I shall
elaborate on this. using a number of examples
to suppaI'! a nd clarify this point.
The moon ha s a low surface gravity. This is
due to the fa ct tha t the moon is smaller in
volume and mass than the earth. Specifically,
the surfa ce gra\'itv is one-sixth that of Earth .
T he low surface gravity is a unique lunar
characLer iHic. We might capitalize upon this
unique pt'opert~· with a number of activities.
The moon would provide a good natural
platform fo r spa ce launches . The moon's
smaller gra \'itational pull would mean that less
energy! fuel ) would be required to boost large
payloads assembled on the moon to other
region s of the solar sys tem. I Approximatel y
95 '.~ of the total weight of the Saturn-Apollo
craft is fu el. Quantitatively to take one pound
from Ea rth to the moon requires about
20.000.000 foo t-pounds of work ; but to go an
additi onal 240 .000 miles starting from the moon
requires on l:: about 300.000 foot-pounds .) Thu s ,
it would be more economical to lalJnch from
the moon if a la rge payload is to be deliver ed to
other members of the sol a r system.
The metallurgist might also capitalize
upon the moon's low surface gravity, Alloys,
which are a blend of different metals , are
sometimes difficult to produce. The different
me ta ls have different densities and freezing
points. While the mixture of metals cools , the
heavier or more dense metal often separates
from the melt and the alloy will not be
homogeneou s. The moon's unique conditions
offer a poss ibility for minimizing this problem.
Since the moon has no appreciable
atmosphere. it is considered to be a " hard "
vacuum. We know that the moon has no
permanent atmosphere-we have been there .
15
But before man visited the moon , he
anticipated this fact. A number of observations
indicated this. When the moon occults or passes
between Earth and a more distant celestial
body , the occultation is sharp . An atmospheric
blanket around the moon would reveal itself by
a gradual dimming of light by the object being
occulted. The terminator, or boundary between
dark and light on the moon 's surface is sharp,
indicating no atmosphere. Lunar craters are
well preserved; there is no sign of weathering
and erosion which accompanies the presence of
an atmosphere. Also, the moon has a low
albedo, that is, only about 0.07 of the light
incident upon the moon's surface is reflected.
Objects with a high albedo have an
appreciable, dctected atmosphere. Theoretical
calculations also indicate that the moon could
not retain an atmosphere. Because of the low
surface gravity , and the high " day" '
temperature (240 0 F J. the average molecular
velocity of most gases exceeds the velocity
necessary for escape from the vicinity of the
moon. Thus. much evidence indicated no
atmosphere on the moon .
The presence of no atmosphere would be of
primary interest to the observational
astronomer. Our knowledge of celestial bodies
other than Earth is a result of the light energy
which we receive from that body. (Visible
light, heat , x-rays , ultraviolet light, radio
waves, etc . may seem unrelated, but they are
all electromagnetic waves.!. Each region of
the electromagnetic spectrum has inherent in
it some piece of information concerning the
body which is emitting or reflecting the light.
Earth's atmosphere will not transmit all
wavelengths or frequencies of light; only
visible light as you and I most frequently think
of light and certain regions of the infrared,
microwave , and shortwave radio are
transmitted by Earth's atmosphere. Not only is
the quantity of light energy determined by our
atmosphere , but its quality is also affected .
The atmosphere , commonly in motion , distorts
incoming signals-resulting in blurred images,
noise. and indis tinct features of an object
being studied . The moon which has no
atmosphere would always have good " seeing "
and no c loudy weather to minimize observing
time . Furthermore, all regions of the
electromagnetic
spectrum
would
be
accessible.
As was discussed previously. the moon 's
period of rotation is equal to its sidereal period
of revolution . A day of light and darkne ss would
be equivalent in length to the synodic month ,
29.5 days. The astronomer observing from the
moon could observe during the lunar night a
length of time equal to fourteen Earth days . In
this way long exposures which would allow one
to penetrate deeply into the universe would be
possible. Perhaps an increased knowledge of
our position in the universe and the events of
cosmic time could be obtained.
The preceding are just a few examples of
how the moon's unique environment might be
utilized to complement Earth 's environment
for conducting certain activities. Other
activities will be proposed . Of course one must
a! ~ o bear in mind that other technological
problems will have to be overcome to allow
man to exist on the lunar surface , but much
research has been conducted to surmount these
other problems.
But perhaps the greatest benefit which
might accrue to mankind as a result of our
lunar exploration and the Apollo Project is that
of a new pe~spe c tive of planet Earth. Frank
Borman, command pilot of Apollo 8 which took
the first men to the vicinity of the moon , looked
back on the Earth as " one world. "
In a broad sense , the charisma of Apollo 8
has implications for a ll mankind. The planet
Earth is not unlike the Apollo spacecraft. The
three astronauts in the command module (or
lunar module) are at the mercy of their closed
system or environment . The capacity of the
command module limits the food supply, the
supply of fuel, the supply of life-supporting
oxygen, the capacity for disposal of body
wastes, in fact , all processes necessary for
survival.
The Earth-as one world-is currently
being faced with a poss ible environmental
crisis. Planet Earth , like the Apollo , has a
definite food-producing capacity, a limited
supply of energy and mineral resources , and a
delicate atmosphere whose equilibrium is
being upset. If Apollo serves as the impetus for
a new perspective upon our environment,