The Moon, Comets, and Asteroids By: Marvette Lacy

Moons

The Motion of The Moon Moves eastward against the background of stars by slightly more than its angular diameter (0.5°) About 13° every 24 hours The eastward movement is the result of the motion of the moon along its orbit around Earth

The Phases of The Moon As the moon orbits Earth, it rotates to keep the same side facing Earth.

The Phases of The Moon The changing shape of the moon as it passes through its cycle of phases is produced by sunlight illumination different parts of the side of the moon we can see.

The Tides Lunar Effect The ebb and flow of the tides Periodic changes in the ocean are caused by the moon’s gravity

The Tides The moon’s gravitational force acting on an object on Earth’s surface is only about 0.0003 percent of Earth’s gravitational force.

The Tides Tides are produced by a difference between the gravitational force acting on different parts of an object

The Tides The side of Earth facing the moon is about 6400km (4000 miles) closer to the moon than is Earth’s center, and the moon’s gravity pulls more strongly on the oceans on the near side than on Earth’s center. Makes the ocean waters flow into a bulge on the side of Earth facing the moon

The Tides A bulge also forms on the side of Earth facing away from the moon. The far side is also 6400 km away from the center and moon’s gravity pulls on it less strongly than it does on Earth’s center. A small force makes the ocean waters on Earth’s far side flow away from the moon

The Tides Because there are two bulges on opposite sides of Earth, the tides rise and fall twice a day, and the time of high and low tide depend on the phase of the moon.

Asteroids

Asteroids Were known as small chunks of rock drifting between the orbits of Mars and Jupiter Evidence shows that they are the last remains of the planetesimals that built the planets 4.6 billion years ago.

Asteroids Metallic, rocky bodies No atmosphere Most reside in the “asteroid belt” A doughnut-shaped ring located between the orbits of Mars and Jupiter Gaspra and Ida are main belt’s asteroids.

Asteroids Asteroids are thought to be primordial material prevented by Jupiter’s strong gravity from accreting into a planet-sized body when the solar system was born.

Asteroids Our understanding of asteroids has been derived from three main sources Earth-based remote sensing Data from the Galileo flybys Laboratory analysis of meteorites

Asteroids Classified into different types according to their albedo, composition derived from spectral features in their reflected sunlight, and infrared similarities to know meteorite types. Albedo refers to an object’s measure of reflectivity, or intrinsic brightness.

Asteroids The majority of asteroids fall into the following three categories: C-type S-type M-type

C-type Carbonaceous 75% of asteroids Like the composition of Sun Hydrogen Helium Other volatiles Inhibit the main belt’s outer regions

S-type Silicaceous 17% of asteroids Composition is metallic iron mixed with iron- and magnesium-silicates Dominate the inner asteroid belt

M-type Metallic Contains many of the rest of the known asteroids Composition is apparently dominated by metallic iron Inhibit the main belt’s middle region

NEAs Near Earth Asteroid Fragments jarred from the main belt by a combination of asteroid collisions and the gravitational influence of Jupiter Nuclei of dead, short-period comets Representative of most or all asteroid types found in the main belt

NEA Groups Amors: Asteroids which cross Mars’ orbit but do not quite reach the orbit of earth. Apollos: Asteroid which cross Earth’s orbit with a period greater than 1year Athens: Asteroids which cross earth’s orbit with periods less than 1 year

NEAs Approximately 250 NEAs have been found to date Estimates suggest at least a thousand NEAs may be large enough to threaten earth.

Comets

Comets Small, fragile, irregularly shaped bodies composed mostly of a mixture of water ice, dust, and carbon-and silicon-based compounds

Comets Have highly elliptical orbits that repeatedly bring them very close to the Sun and then swing them into space

Comets The solid core is called the nucleus, which develops a coma with one or more tails when a comet sweeps close to the Sun. Coma and Tails A coma is a dusty and fuzzy cloud around the nucleus Tail extends from the comet and points away from the Sun Coma and tails of a comet are transient features, present only when the comet is near the Sun

Types of Tails Dust Tail Yellow Contains small, solid particles Sunlight acts on these small particles, gently pushing them away from the comet’s nucleus

Types of Tails Gas Tails Blue Forms when ultraviolet sunlight rips one or more electrons from gas atoms in the coma making them into ions. A solar wind then carries them outward, away from the Sun

Origin of Comets Comets are found in two main regions of the cosmos Kuiper belt Oort Cloud

Kuiper Belt Short period comets—comets that frequently return to the solar system—originate here Located within the solar system’s ecliptic plane, beyond the orbit of Neptune The first object was found in 1992

Oort Cloud Long period comets are thought to emanate from a vast, spherical cloud of frozen bodies Made up of frozen ammonia, methane, cyanogen, water ice, and rock. Occasionally, a gravitational disturbance causes one of these bodies to begin a journey toward the inner solar system.

Impact Many bodies have struck Earth and the Moon in the past Some widely accepted theory The extinction of dinosaurs Help formed the chemical building blocks of life and much of earth’s water arrived on asteroids or comets that bombarded the planet in its youth

References Foundations of Astronomy http://amazing-space.stsci.edu/resources/explorations/comets/teacher/scientificbacground.com http://nssdc.gsfc.nasa.gov/planetary/text/asteroids.txt