Fine Dust

The lunar soil, termed regolith, is fine-grained, fragmented bedrock. It is dustlike on the surface, but the grains get larger with depth. Astronauts' boots left crisp footprints.

EARTH AND MooN pARTNERSHip

The Moon takes 27.3 days to complete one elliptical orbit around Earth. As it moves, Earth orbits around the Sun. It takes 29.5 days for the Moon to return to the same position relative to the Sun in Earth's sky, and complete its cycle of phases. The Moon's gravity pulls on Earth, making the oceans on either side of the planet bulge, in turn producing the tides. Tidal forces slow down Earth's spin, with the result that the Moon is moving away from Earth by about 1 in (3 cm) each year.

tidal bulges

Two bulges in Earth's oceans (exaggerated here) are created by the gravitational interaction of Earth and the Moon. As Earth spins, the bulges of water sweep over the planet's surface, creating changes in sea level—high and low tides.

synchronous rotation

The Moon spins around once every 27.3 days. This is the same length of time that it takes to make one orbit around Earth. As a result of this synchronization of the Moon's rotation and orbit, the Moon keeps the same side, termed the near side (marked here by a red dot), facing Earth.

imaginary point always faces the Earth

Earth's spin causes tidal bulges to sweep over surface tidal bulges

Earth's spin causes tidal bulges to sweep over surface tidal bulges

Low TiDE iN oREGoN

The time of high tide depends on the position of the Moon in the sky. Tide height changes during the lunar cycle.

pull of the Moon

pull of the Moon

Low TiDE iN oREGoN

The time of high tide depends on the position of the Moon in the sky. Tide height changes during the lunar cycle.

phases of the moon

Sunlight always lights up one half of the Moon, just as it lights up one half of Earth. The half that is lit changes, as the Moon spins and moves along its orbit. From Earth, just one side of

Moon as seen from Earth the Moon is visible. This is at times fully lit, partially lit, or unlit, giving the impression of a different shape. The changing views we have of the Moon are known as its phases; a complete cycle of phases takes 29.5 days.

waning gibbous waning gibbous

Moon as seen from Earth sunlight new moon

first quarter waxing gibbous sunlight changing views

When the Moon is between Earth and the Sun, the side facing Earth is unlit; this is a new moon. As the Moon moves, the sunlit area grows (waxes) until it is fully lit (full moon) and then decreases (wanes) until unlit.

first quarter waxing gibbous new moon the moon 99

lunar eclipses

When the Sun, Earth, and Moon are aligned, a lunar eclipse can occur. The Moon can move into the shadow cast by Earth. If it is completely within the shadow, the Moon is totally eclipsed. If only partly covered by shadow, the Moon is in partial eclipse. An eclipse is visible from anywhere on Earth, as long as the Moon is above the horizon.

only a slight darkening of the Moon may occur in the light outer shadow how lunar eclipses occur

Earth blocks the Sun's light and casts a shadow into space. The Moon moves into the shadow. In the darkest part, it is totally eclipsed, and can appear reddish when sunlight is bent into the shadow by Earth's atmosphere. Lunar eclipses happen up to three times a year.

sunlight inner, darker shadow (umbra)

only a slight darkening of the Moon may occur in the light outer shadow i

outer, paler shadow I (penumbra)

onset of eclipse

The Moon has moved into Earth's shadow; part of its disk is obscured.

inner, darker shadow (umbra)

outer, paler shadow I (penumbra)

red moon

As the Moon moves farther into Earth's shadow, its face turns a pinkish red.

over halfway

Earth is blocking the sunlight from most of the Moon. The crescent left shines brightly.

close to totality

The eclipse is about to be total. Except for a sunlit sliver, the Moon is within Earth's shadow.

Earth

MAN on THE MOON

Twelve men from six different Apollo space missions walked on the Moon between July 1969 and December 1972. They collected over 838 lb (380 kg) of lunar rock and soil from six different sites.

missions to the moon

Over 60 craft have journeyed to the Moon. Most flew in the decade from 1959 to 1969, when both the United States and the Soviet Union were preparing to put a human on the Moon. This aim was fulfilled by the United States in 1969 (see pp.28-29). About the same time, Soviet probes returned samples of the Moon's soil, and two robotic craft, Lunokhods 1 and 2, roved across its surface. No further craft were sent until the 1990s. Now, more probes, which study the Moon from lunar orbit, are in operation, or are planned.

smart-1

The European Space Agency's Smart-1 is the first European craft to be sent to the Moon. Launched in September 2003, one of its tasks is to make an inventory of chemical elements in the lunar surface.

lunar topography

Accurate height measurements were made of the surface by the Clementine probe in 1994. In this map, made from Clementine data, blue is low, green medium, and red high. The Moon's far side is left, the near right.

mapping the moon

Humans have observed the Moon ever since they looked skyward. Its full bright disk lit up the dark night hours for early people, and its changing face and movement marked the passage of time. The newly invented telescope was turned moonward in the 17th century, when the first lunar maps were made. The first photographic atlas came in 1897. Decades later, the space age offered the chance to see the far side and observe more detail. During 1966—7, five Lunar Orbiter craft mapped 99 percent of its surface.

Aristarchus Crater

)Uta

OCEANUS F»f observing the moon

The Moon, which shines by reflecting sunlight, is easily spotted in Earth's sky. It only goes unnoticed near new moon, when its near side is unlit. But even then, the unlit part can receive some light reflected from Earth, known as Earthshine. The Moon is close enough and bright enough for us to see detail. Two types of terrain are clearly visible: the large, dark plains (maria); and the brighter, heavily cratered highland regions pjo"1" Carpa*"5

Kepler Crater

Copernicus Crater

Grimaldi Crater

MARE COGNiTUM

Gassendi Crater

Alphonsus Crater

MARE NUBiUM

Gassendi Crater

Alphonsus Crater

MARE NUBiUM

viewed by naked eye

The Moon is easy to see, and moves quite rapidly. Dark and light features are apparent.

viEwED BY BiNocuLARS

The Moon is still a whole disk but the image is larger and more detailed with more features.

viewed by telescope

A portion of the disk is now seen. Innumerable craters and individual mountain ranges are in view.

viewed by naked eye

The Moon is easy to see, and moves quite rapidly. Dark and light features are apparent.

viEwED BY BiNocuLARS

The Moon is still a whole disk but the image is larger and more detailed with more features.

viewed by telescope

A portion of the disk is now seen. Innumerable craters and individual mountain ranges are in view.

the moon

MARE FRiGORiS

Aristoteles , Crater m

Eudoxus Crater

Lacus Somniorum

MARE sEREmTATis

MARE VAPoRuM

Posidonius Crater

Proclus Crater a s

Is mare

TRANQUiLLiTATiS

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