This is one of the more famous images of the Earth from the Apollo program, taken by the Apollo 8 astronauts as they became the first humans to circumnavigate the Moon. Title: View of rising Earth about five degrees above the Lunar horizon Description: The rising Earth is about five degrees above the lunar horizon in this telephoto view taken from the Apollo 8 spacecraft near 110 degrees east longitude. The horizon, about 570 kilometers (250 statute miles) from the spacecraft, is near the eastern limb of the Moon as viewed from the Earth. On the earth, the sunset terminator crosses Africa. The south pole is in the white area near the left end of the terminator. North and South America are under the clouds. The lunar surface probably has less pronounced color than indicated by this print.

PHOTO CAPTION GALILEO December 22, 1992 P-41508 TOP GLL/EM2 3 Eight days after its encounter with the Earth, the Galileo spacecraft was able to look back and capture this remarkable view of the Moon in orbit about the Earth, taken from a distance of about 6.2 million kilometers (3.9 million miles), on December 16. The picture was constructed from images taken through the violet, red, and 1.0-micron infrared filters. The Moon is in the foreground, moving from left to right. The brightly-colored Earth contrasts strongly with the Moon, which reflects only about one-third as much sunlight as Earth. Contrast and color have been computer-enhanced for both objects to improve visibility. Antarctica is visible through clouds (bottom). The Moon's far side is seen; the shadowy indentation in the dawn terminator is the south-Pole/Aitken Basin, one of the largest and oldest lunar impact features, extensively studied from Galileo during the first Earth flyby in December 1990. The Galileo project, whose primary mission is the exploration of the Jupiter system in 1995-97, is managed for NASA's Office of Space Science and Applications by the Jet Propulsion Laboratory.

Earth’s Moon Earth’s only natural satellite We are the only planet with just one moon When compared to the host planet – our moon is the largest proportionally 240,000 miles from Earth

Earth / Moon Comparison Diameter – 7930 miles 23.5 degree tilt (seasons) Surface Temperatures -100°F to 120°F Thick atmosphere Liquid water at surface Length of day – 24 hours Diameter – 2160 miles (≈1/4 the diameter of the Earth) 7° tilt (no seasons) Surface temps -243°F to 224°F No atmosphere (dry and airless) Length of day – 27.3 Earth days

The Lunar Landscape The moon’s surface includes 3 major areas Highlands (Lunar terrae - latin for moon “land”) These are the bright areas of the moon Heavily cratered Lunar maria – ( moon seas) Dark, smooth areas on the moon Craters Formed by impacts from outer space

Moon’s Surface Regolith - layer of rock and rock dust covering the surface of the moon Sometimes called “lunar soil” – has no organic material like Earth soil 3 to 15 meters deep 4 Layers Lunar regolith is formed by the bombardment of meteoroids

Meteors, Meteoroids, Meteorites Meteoroid – a chunk of rock or dust in space Meteor – when a meteoroid comes in contact with Earth’s atmosphere and produces a streak of light Meteorite – when a meteor hits the Earth’s surface

Impact craters on the Moon Caused by meteoroids Some as large as the state of Connecticut – others smaller than the head of a pin This portion of the Moon is covered by numerous circular holes. These are impact craters, each of which was formed when an asteroid or comet collided with the Moon's surface. The large number of craters in this region indicates that this part of the Moon is quite ancient. Geologic processes have not erased the craters with time.

Types of Craters Simple Craters Bowl shaped with rounded, or small flat floors This image shows a simple crater on Mars that has no central peak or terraces around its edges. The crater is 2 kilometers (about 1 mile) wide. An extensive blanket of ejecta covers the area around the rim. Image from the Mars Global Surveyor, courtesy of the Lunar and Planetary Institute.

Types of Craters Complex Large craters Usually have terraced walls Have a central peak (or peaks) that rise up from a broad, flat floor Copernicus is a large crater (93 kilometers or 60 miles wide) on the Moon. The inner walls of the crater have collapsed to form a series of step-like terraces, and a central peak is visible in the center of the image. Apollo 17 image courtesy of NASA.

Types of Craters Impact Basins Largest type of impact crater Usually over 250 miles wide Impact basins are very large impact structures that are more than 300 kilometers (185 miles) in diameter. The largest impact basin on the Moon is 2500 kilometers (1550 miles) in diameter and more than 12 kilometers (7 miles) deep. Large impact basins are also found on other planets, including Mars and Mercury. The large circular dark areas in the image are impact basins, created as huge impactors struck the Moon. Lava later flowed across the low floors of the basins, giving them a darker, smoother appearance than the surrounding, brighter highlands. The dark basins can be seen by the naked eye.

Parts of a crater Walls – like the sides of a bowl Floor – Rim – Vary in steepness May have giant steps called terraces Floor – May be flat or shaped like a bowl Below ground unless filled in with lava Rim – Ring shaped pile of debris Highest point along edge of crater Ejecta – The debris that shoots out or ejects from the impact site Becomes thinner away from the crater

Parts of a crater Rays Bright streaks that start at the rim and extend outward for great distances

Large impacts cause the rock at the impact area to behave as a liquid Central Peak mountains that form at the center of a crater due to the impact Only found craters larger than 40 km (25 miles) diameter

Barringer Crater - Arizona

Formation of the Moon

Theories on Moon Formation Capture Hypothesis Earth captured a fully formed moon in its gravitational pull Problem Highly unlikely – a close encounter would result in a collision or sending moon on different orbit around the sun

Theories on Moon Formation Fission Hypothesis Earth was spinning so fast a piece flew off forming the moon Problem No way to explain how Earth was spinning so fast and why we aren’t spinning that fast today

Theories on Moon Formation Double-Planet Hypothesis Earth and Moon formed together from the start Problem Cannot explain how the moons material got into orbit and stayed there (did not crash into Earth) Cannot explain the moons rotation and motion around the Earth

Formation of the Moon Collision- ring theory

Moon Formation Hypothesis Collision-Ring Theory A rogue planet the size of Mars collided with a very young Earth Knocked material off into space which clumped together due to gravity and became our Moon

Collision Ring Theory Explains The way Earth Spins Earth’s Tilt Why Earth has larger metallic core than the Moon Same type / age of rocks found on Moon as on Earth

The Origin of the Moon The theory that seems to best fit the evidence is called the collision- ring theory About 4.5 billion years ago the solar system was full of rocky debris (some the size of small planets) Scientists theorize a planet-sized object collided with the earth to form the moon