Transcript Document
A Closer look at… Our Moon Created by: Mrs. Bodine-Donahue The moon is a “natural satellite”. A satellite is anything the orbits the earth. Artificial satellites have four main uses: – Communications – Monitoring the weather – Observing the Earth – Exploring the solar system The moon is a cold, dry orb whose surface is studded with craters and strewn with rocks and dust. The moon has no atmosphere. Recent lunar missions indicate that there might be some frozen ice at the poles. The Moon’s movement The moon revolves around the Earth in about one month (27 days 8 hours). It rotates around its own axis in the same amount of time. The same side of the moon always faces the Earth; it is in a synchronous rotation with the Earth. The Moon’s Orbit The Moon and Earth both orbit around a point between their centers called the center of mass of the Earth-Moon system The center of mass then follows an elliptical orbit around the Sun This Picture Distorts the Earth-Moon Distance An Everyday Example of Center of Mass Motion Motion of the Earth-Moon Center of Mass How far away is the Moon? The moon is about 238,900 miles (384,000 km) from Earth on average. At its closest point the moon is 221,460 miles (356,410 km) from the Earth. At its farthest approach the moon is 252,700 miles (406,700 km) from the Earth. Size of the Moon The moon's diameter is 2,140 miles (3,476 km), the Earth is 7,900 miles (12,742 km) in diameter. That's how far you would have to tunnel to dig to the other side of the Earth! The circumference of the moon is 6,790 miles (10,864 km). The circumference of the earth at the equator is 24,901.55 miles (40,075 km). How much does the Moon weigh? The moon's mass is about 1/81 of the Earth's mass. The moon's gravitational force is only 17% of the Earth's gravity. For example, a 100 pound person would weigh only 17 pounds on the Moon. The Atmosphere on the Moon TEMPERATURE The temperature on the Moon ranges from daytime highs of about 130°C = 265°F to nighttime lows close to -310 °F. ATMOSPHERE The moon has no atmosphere. On the moon, the sky is always appears dark, even on the bright side (because there is no atmosphere). Also, since sound waves travel through air, the moon is silent; there can be no sound transmission on the moon. The surface of the moon is scarred by millions of (mostly circular) impact craters, caused by asteroids, comets, and meteorites. There is no atmosphere on the moon to help protect it from bombardment from potential impactors (most objects from space burn up in our atmosphere). Also, there is no erosion (wind or precipitation) and little geologic activity to wear away these craters, so they remain unchanged until another new impact changes it. The Moon’s airless, dry surface is covered with plains and craters The Earth-facing side of the Moon displays light-colored, heavily cratered highlands and dark-colored, smooth-surfaced maria The Moon’s far side has almost no maria Another View of the Moon The Moon’s Surface – Close up Virtually all lunar craters were caused by space debris striking the surface There is no evidence of plate tectonic activity on the Moon The maria formed after the surrounding light-colored terrain, so they have not been exposed to meteoritic bombardment for as long and have fewer craters Human exploration of the lunar surface Much of our knowledge about the Moon has come from human exploration in the 1960s and early 1970s and from more recent observations by unmanned spacecraft Man on the Moon There have been 6 missions to the moon, including orbiters missions and moon landings. On July 20, 1969 Neil Armstrong was the first person to set foot on the moon. His first words upon stepping down the Lunar Module's ladder onto the lunar surface were, "That's one small step for man, one giant leap for mankind." Aldrin described the lunar scenery as "magnificent desolation." 12 astronauts have walked on the moon. All were American. How did the Moon form? Most scientists believe that the moon was formed from the ejected material after the Earth collided with a Mars-sized object. This ejected material gathered into the moon that went into orbit around the Earth. This catastrophic collision occurred about 60 million years after Earth itself formed (about 4.3 billion years ago). This is determined by the dating of moon rocks. Meteoroid impacts have been the only significant erosion agent on the Moon The Moon’s regolith, or surface layer of powdered and fractured rock, was formed by meteoritic action All of the lunar rock samples are igneous rocks formed largely of minerals found in terrestrial rocks Mare basalt The lunar rocks contain no water They differ from terrestrial rocks in being relatively enriched in the refractory elements and depleted in the volatile elements Highlands anorthosite Impact breccia Lunar rocks reveal a geologic history quite unlike that of Earth The anorthositic crust exposed in the highlands was formed between 4.0 and 4.3 billion years ago The mare basalts solidified between 3.1 and 3.8 billion years ago The Moon’s surface has undergone very little change over the past 3 billion years The Moon has no global magnetic field but has a small core beneath a thick mantle Source: Dr. James Regas Cal State Chico Source: Dr. James Regas Cal State Chico Source: Dr. James Regas Cal State Chico Source: Dr. James Regas Cal State Chico Most Likely Theory of Formation of the Moon The collisional-ejection theory – Successfully explains most properties of the Moon – Hypothesizes that the proto-Earth was struck by a Mars-sized protoplanet and that debris from this collision coalesced to form the Moon The Moon was molten in its early stages, and the anorthositic crust solidified from low-density magma that floated to the lunar surface The mare basins were created later by the impact of planetesimals and filled with lava from the lunar interior Other alternate theories that fail in areas – Co-creation (sister), fission, capture Source: Dr. James Regas Cal State Chico Source: Dr. James Regas Cal State Chico Source: Dr. James Regas Cal State Chico