ABOUT THIS ISSUE
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
Editorial Committee: James S. Wilson, Robert F. Clarke, Gilbert A. Leisman, Harold Durst
Exofficio: Dr. Edwin B. Kurtz, Head, Dept. of Biology
Online edition by: Terri Weast
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ABOUT THE AUTHOR
DeWayne Backhus is an Assistant Professor in the Physical Science Division of Kansas State Teachers College.
by DeWayne Backhus
The Moon's Position in 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, although 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.
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.
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.
Revolution refers to the motion of a body about some point outside of that body.
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).
The Apollo Project personnel have relied upon the relationship between the sun, Earth, and moon for the manned moon landings. All 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 twelve 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.
Figure 3. A top-view sketch of the sun, Earth (at E1 and E2), and the moon at M1 ,M2, and M3. Since the star is very far away, the line of sight to the moon and the star at Earth position E1 is parallel to the line of sight to M2 and the star from Earth position E2.
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 655h 43m, or 27.3 days. The moon's position at the end of this time interval is shown at M2: the Earth is at E2. But the moon has not completed one full revolution with respect to the sun. Because the sun is closer: 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 days. 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.
TABLE I. TIME OF MOONRISE*
|Phase||Position in Figure 1||Appearance, Figure 2||Time of Moonrise||Position of observer on Earth in Figure 1|
|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|
|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||Vicinity of h|
*The time of moonrise is simplified; times of sunrise and sunse t are assumed to be 6 AM and 6 PM
respectively. Thus, some adjustment in times of rise (a nd set) will have to be made with the
seasonal variations of Earth.
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 same side or hemisphere toward the Earth. Thus, no Earth observer has ever seen the "far-side" or other hemisphere of the moon. Man's first photographs of the far-side of the moon came as a result of the Soviet Union's Luna 3 efforts on October 7, 1959. Since then both the Soviet Union and the United States have mapped the far-side in some detail. The Apollo 8 crew (Borman, Lovell, and Anders) were the first 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 same 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. Using Figure 1, moon position A. imagine an object or lunar feature on the surface of the moon's dark side. and in the center of the hemisphere of the moon toward Earth. As the moon revolves 90° about Earth from A to C, the moon also rotates 90° counterclockwise 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 never 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 sky 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 which we experience on Earth as a consequence of the spatial relationships 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 phase (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 system (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.
Figure 4. Elements of the moon's elliptical orbit about planet Earth. The distance from perigee to apogee is about 476,000 miles.
Let us now consider the sun, Earth, and moon system. The moon's orbit about the Earth is not circular, it is elliptical. (See 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 252,000 miles away. The moon's average distance 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.
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).
Figure 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 (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 into 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 because the moon revolves in its orbit counterclockwise (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.)
Figure 6. 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.
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 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.
Figure 7. An edge view of the plane of the ecliptic, the Earth's plane of 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'.
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 50 degrees 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 nodes, 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.
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.
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.
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).
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 desire to "get there" because it exists.
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 this 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 hardlanding (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.
During the mid-sixties a controversy was raging concerning the nature of the lunar surface. 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 hypothesis, 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 superficial 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 basalt-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.
Also 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 weeks duration. Also, the Gemini project involved space rendezvous-a technique to be used by Apollo (involving the command module and the lunar module) for economizing 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.
In 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 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 design of the module's hatch (or door). The 100 per cent oxygen environment was dropped in favor of a nitrogen-oxygen atmosphere. The hatch, which had been designed to open inward to prevent opening in space because of the differential pressure within the module and the "vacuum" of space, was redesigned to open
outward to enhance escape if necessary prior to launch. But the interest of the public in Apollo was 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. Apollo 9 followed in February of 1969. Astronauts McDivitt, 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 miles of the lunar surface prior to rendezvous with the command module and return to Earth. It was this close encounter of the Apollo 10 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 lunar 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 surface; 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 disturbances, 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 was possibly the most successful of all Apollo flights. Certainly, future lunar exploration will continue, but the general public has experienced the peak of excitement with respect to 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 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 lunar craters formed as a result of meteorite impact 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 reasonably 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 maria, the frequency of meteorite impact has not been nearly so great a in the first billion years of the history of the moon.
There are still many unanswered questions concerning the moon's history and the history of our solar system. In fact today only few questions have been answered, many more questions have been raised by the scientists studying lunar materials, processes, and history. Did the maria form as a result of internal forces on the moon, indicating that the lunar interior is hot and active? Or were the maria formed as a result of external forces - such as meteorite impact and subsequent shock melting? Similarly, are craters formed from meteorite impact or are they the result of volcanic activity similar to volcanic activity witnessed on Earth? What events formed the "ray" system of such young craters as Copernicus, Tycho, and Kepler? Are these ray systems the result of fissure or flank volcanic eruptions or are ray systems produced by ejecta or debris 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 study of the moon. The possibility also exists that the moon was a warm and active body during its first billion years of existence, and during the last 3.5 billion years it has been a cold body with external forces shaping its surface. Thus, more questions have been rai sed about the moon since the Apollo landings than have been answered.
The Moon, Man, and the Future
Certainly man's exploration of the moon has just begun. Future scientific exploration efforts will be made to provide us insights for the solutions to some of the questions 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 deterrent to crime; and that the moon be
made a universal exile or refuge from Earth. These, however, are not reasonable, especially the one which would upset the balance of nature on Earth.
I believe that man's future ventures on the moon will capitalize upon the unique environment which the moon possesses. Thus, the moor, will not provide a place for competition with usual Earth activities, but it
will complement Earth with respect to a number of activities which are not carried out effectively in Earth's environment. I shall elaborate on this, using a number of examples to support and clarify this point.
The moon has a low surface gravity. This is due to the fact that the moon is smaller in volume and mass than the earth. Specifically, the surface gravity is one-sixth that of Earth.
The low surface gravity is a unique lunar characteristc. We might capitalize upon this unique property with a number of activities. The moon would provide a good natural platform for space launches. The moon's
smaller gravitational pull would mean that less energy (fuel) would be required to boost large payloads assembled on the moon to other regions of the solar system. (Approximately 95% of the total weight of the Saturn-Apollo craft is fuel. Quantitatively to take one pound from Earth to the moon requires about
20.000.000 foot-pounds of work; but to go an additional 240,000 miles starting from the moon requires only about 300,000 foot-pounds.) Thus, it would be more economical to launch from the moon if a large payload is to be delivered to other members of the solar 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 metals 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 homogeneous. The moon's unique conditions offer a possibility 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. 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, detected 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 degrees F), 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 indistinct features of an object being studied. The moon which has no atmosphere would always have good "seeing" and no cloudy 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 darkness 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 also 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 perspective 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 all 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 possible 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, perhaps we can attack these problems of humanity with the same determination as was shown by the scientists, engineers, and technicians responsible for footsteps on the moon. James Lovell stated his feelings succinctly: "The vast loneliness up here is awe-inspiring, and it makes you realize just what you have back there on Earth. The Earth from here is a grand oasis in the big vastness of space."
Individualized instruction, behavioral objectives, accountability - these "in" words become more than just words in a course called Biology 504 (3 credits) which will be offered Monday evenings (7 to 10 p.m.) during the spring semester. A how-to-do-it course, Biol. 504, will help you construct objectives for your courses. For more information write Dr. E. B. Kurtz, Department of Biology, KSTC, Emporia, Kansas 66801.
Human ecology and related environmental problems has been the subject of three Extension courses in Marysville and Salina. A fourth course is scheduled for the spring term in Topeka. If you have a group of 20 or more citizens interested in learning about human ecology (BioI. 537, 3 credits) , write the Director of Extension, KSTC, and arrangements will be made to have an extension course on human ecology in your area.
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