Early Studies

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Investigations of the Moon and some understanding of lunar phenomena can be traced back to a few centuries BCE. In ancient China the Moon's motion was carefully recorded as part of a grand structure of astrological thought. In both China and the Middle East, observations became accurate enough to enable the prediction of eclipses, and the recording of eclipses left data of great value for later scientists interested in tracing the history of the Earth-Moon system. Several early Greek philosophers saw reason to believe that the Moon was inhabited, although they did not base their conclusion on scientific principles. The Greek astronomer and mathematician Hipparchus, on the other hand, took an experimental approach: observing Earth's round shadow creeping across the Moon during a lunar eclipse, he concluded that Earth must be spherical and that the Moon was an independent world, and he correctly explained the Moon's phases and accurately estimated the distance between the two bodies. Later, Mayan calendars were constructed that reflected the results of careful observation and longrange prediction.

For centuries, knowledge about the Moon accumulated slowly, driven by astrological and navigational needs, until an outburst of progress began in the Renaissance. In the early 1600s the German astronomer Johannes Kepler used observations made by Tycho Brahe of Denmark to find empirically the laws governing planetary motion. Kepler wrote a remarkable work of science fiction, Somnium ("The Dream"), which describes the life of imagined inhabitants of the Moon and correctly portrays such facts as the high temperature of the Moon's sunlit side. In 1609-10 Galileo began his telescopic observations that forever changed human understanding of the Moon. Most effort hitherto had been devoted to understanding the movements of the Moon through space, but now astronomers began to focus their attention on the character of the Moon itself. Some milestones in human exploration and understanding of the Moon are given in the table.

HISTORY OF LUNAR OBSERVATION AND EXPLORATION

time period

accomplishment

prehistoric and early historic times

Basic knowledge of Moon's motion, phases, and markings is gathered and expressed in myth and legend.

500 BCE to 150 CE

Phases and eclipses are correctly explained; Moon's size and distance from Earth are measured.

Middle Ages

Lunar ephemeris is refined.

Renaissance

Laws of motion are formulated; telescopic observations begin.

19th century

Near-side lunar mapping is completed; atmosphere is proved absent; geologic principles are applied in volcanism-versus-impact debate over formation of Moon's landscape.

1924

Polarimetry studies show that lunar surface is composed of small particles.

1927-30

Surface temperatures are measured for lunar day and night and during eclipses.

time period

accomplishment

1946

Radar echoes are reflected from Moon and detected for first time.

1950-57

Theories of Moon's formation are incorporated in efforts to explain origin of solar system; radiometric age dating is employed in meteorite research; lunar subsurface temperatures are measured by microwave radiometry; relative ages of lunar features are derived from principles of stratigraphy (study of rock layers and their chronological relationship).

1959

Luna 2 spacecraft becomes first man-made object to strike Moon; global magnetic field is found to be absent; Luna 3 supplies first far-side images.

1960

Detailed measurements of lunar surface cooling during eclipses are made from Earth.

1964

Ranger 7 transmits high-resolution pictures of Moon.

1966

Luna 9 and Surveyor 1 make first lunar soft landings; Luna 10 and Lunar Orbiter 1 become first spacecraft to orbit Moon.

1967

First measurements made of lunar surface chemistry.

1968

Mascons are discovered in analysis of data from Lunar Orbiters; Apollo 8 astronauts orbit Moon.

1969

Apollo 11 astronauts become first humans to walk on Moon; lunar samples and data are returned to Earth.

1969-74

Manned Apollo orbital and surface expeditions and automated Luna flights explore Moon's lower latitudes; Apollo program is completed.

1970s-present

Lunar studies are continued using samples returned by Apollo and Luna missions, meteorites originating from Moon, and data gathered by Earth-based mineralogical remote-sensing techniques.

1990

Galileo spacecraft collects compositional remote-sensing data during lunar flyby, demonstrating potential for future orbital geo-chemical missions.

1994

Orbiting Clementine spacecraft provides imagery, altimetry, and gravity maps of entire Moon.

1998-99

Orbiting Lunar Prospector spacecraft maps lunar surface composition and magnetic field; its neutron spectrometer data confirm presence of excess hydrogen at both poles, suggesting presence of water ice there.

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