James T. Shipman Jerry D. Wilson Charles A. Higgins, Jr. Moons and Smaller Solar System Bodies Chapter 17

Sec 17.1 Structure, Origin, and Features of the Earth’s Moon July 20, 1969 – humans first landed on moon Retroreflector – placed on moon and designed to reflect a laser beam from Earth Rates of Continental Drift on Earth, change in Earth’s tilt, distance to moon, Gravitational Constant ( G ) Average distance = 384,000 km (240,000 mi) Section 17.1

Sec 17.1 Structure, Origin, and Features of the Earth’s Moon Second brightest object in the sky “moon” – unknown origin of the word Many primitive and modern societies base their religious ceremonies on the cycles of the moon (e.g., new and full moons). Our month is based on moon’s cycle. One complete revolution = 29.5 days (approx.) The moon rotates on its axis at the same rate, and therefore we only see one side of the moon. This is called synchronous rotation

Sec 17.1 Structure, Origin, and Features of the Earth’s Moon Avg. Density = 3.3 g/cm 3 ¼ Earth’s diameter Lunar mass = 1/81 Earth masses 1/6 Earth’s gravity (g = 1.5 m/s 2 Albedo = 0.07 Age = byr No magnetic field Core: Inner core: solid: iron rich Outer core: solid Rocky mantle: Crust Regolith: (hardened crust)

Sec 17.1 Structure, Origin, and Features of the Earth’s Moon Impact theory Composition of lunar mantle and crust similar to Earth’s mantle. Section 17.1

Sec 17.1 Structure, Origin, and Features of the Earth’s Moon Section 17.1

Sec 17.1 Structure, Origin, and Features of the Earth’s Moon A unique steep slope on the eastern side of Mare Nubium The wall is 113 km long by 244 m in height. Section 17.1

Sec 17.2 Lunar Motion Effects: Phases, Eclipses, and Tides The lunar orbital plane does not coincide with Earth’s orbital plane. Approximately 5 o with respect to Earth’s orbital plane. Due to this 5 o tilt, it is possible for the moon to be directly overhead at any latitude between 28.5 o N and 28.5 o S. Both the rotation of the Earth on its axis and the moon’s revolution around the Earth are counterclockwise (from a N pole perspective). Section 17.2

Sec 17.2 Lunar Motion Effects: Phases, Eclipses, and Tides Section 17.2

Sec 17.2 Lunar Motion Effects: Phases, Eclipses, and Tides Occurs when earth, Sun, and moon are all in the same plane, with the moon positioned between the Sun and Earth At this position, the dark side of the moon is fully toward the Earth (“dark of the moon”). Section 17.2

Sec 17.2 Lunar Motion Effects: Phases, Eclipses, and Tides The “observer” is looking south; therefore east is on the left. Section 17.2

Sec 17.2 Lunar Motion Effects: Phases, Eclipses, and Tides Section 17.2

Sec 17.2 Lunar Motion Effects: Phases, Eclipses, and Tides The umbra and penumbra are, respectively, the dark and semidark shadows cast on the Earth by the Moon Section 17.2 A solar eclipse

Sec 17.2 Lunar Motion Effects: Phases, Eclipses, and Tides Section 17.2 Umbra of the Moon’s shadow does not reach all the way to the Earth Solar corona during a total solar eclipse

Sec 17.2 Lunar Motion Effects: Phases, Eclipses, and Tides Section 17.2 A lunar eclipse

Sec 17.2 Lunar Motion Effects: Phases, Eclipses, and Tides There is a 5.13  angle between the Orbital Planes of the Earth and the Moon Therefore, the paths of the two planes intersect at only two points during the monthly cycle The points where the Moon’s path crosses the ecliptic are called the nodes Ascending node – the point of crossing going northward Descending node – the point of crossing going southward Section 17.2

Sec 17.2 Lunar Motion Effects: Phases, Eclipses, and Tides Section 17.2

Sec 17.2 Lunar Motion Effects: Phases, Eclipses, and Tides Neap tide occurs when the Sun and the Moon are at angles of 90 o with respect to the Earth Tidal differences are minimal Neap tides occur during first and last quarter phases Spring tides occurs when the Sun and Moon are inline with the Earth Tidal differences are extreme Spring tides occur during new and full moon phases Section 17.2

Sec 17.2 Lunar Motion Effects: Phases, Eclipses, and Tides The regular tidal cycle retards the Earth’s rotation at a rate of about s per century Since angular momentum must be conserved, this decrease in Earth’s angular momentum results in an increase in the moon’s angular momentum The moon’s orbit is increasing about 1.3 cm/y If we went back 1 billion years, the solar day would have been 5.6 h shorter, and the moon would have been 13,000 km closer to Earth Section 17.2

Sec 17.3 Moons of the Terrestrial Planets Mercury: No moons Venus: No moons Earth: 1 moon Mars: 2 known moons Phobos (“fear”) and Deimos (“panic”) Section 17.3

Sec 17.4 Moons of the Jovian Planets Jupiter: 64 known moons The four largest were discovered in 1610 by Galileo, and are therefore called the “Galilean Moons.” They are Io, Europa, Ganymede, and Callisto Section 17.4

Sec 17.4 Moons of the Jovian Planets Section 17.4 Titan: Saturn’s largest moon

Section 17.4 Sec 17.4 Moons of the Jovian Planets Miranda: A moon of Uranus

Sec 17.4 Moons of the Jovian Planets Section 17.4

Sec 17.6 Small Solar System Bodies Asteroids Meteoroids, Meteors, and Meteorites Comets Interplanetary Dust Section 17.6

Sec 17.6 Small Solar System Bodies Asteroids - over 20,000 named or numbered objects that orbit the Sun in a belt between Mars and Jupiter This belt contains millions of asteroids About 600,000 are bright enough to be photographed by Earth-based telescopes Sometimes referred to as minor planets Section 17.6

Sec 17.6 Small Solar System Bodies Section 17.6

Sec 17.6 Small Solar System Bodies Meteoroid – interplanetary metallic and stony objects that range in size from sub-millimeter to 100’ of meters. Meteor – a meteoroid that enters the Earth’s atmosphere and becomes luminous – a “shooting star.” Meteorite – a meteor that survives the flight through the Earth’s atmosphere and strikes the Earth. Section 17.6

Sec 17.6 Small Solar System Bodies Great Barringer Crater 50,000 years old near Winslow, AZ. Section 17.6

Sec 17.6 Small Solar System Bodies Comets: Relatively small objects that are composed of dust and ice, and revolve around the Sun in a highly elliptical orbit Section 17.6

Sec 17.6 Small Solar System Bodies Note how the comet’s tail is affected by and is directed away from the Sun, and does not indicate the comet’s direction of movement. Section 17.6

Sec 17.6 Small Solar System Bodies A tremendous amount of interplanetary dust can be found throughout the Solar System. Two celestial phenomena can be observed and photographed, showing that dust particles do exist: Zodiacal light—a faint band of light along the zodiac. Gegenshein “counterglow”—due to sunlight reflected from dust particles Section 17.6