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Chapter 4: Earth & its Moon

Fig. 7.1 (CP):The terrestrial worlds, shown to scale, along with surface close-ups from orbiting spacecraft. All the photos were taken with visible light except the Venus close-up (radio waves).

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Fig. 7.2: Interior structures of the terrestrial worlds, shown in scale and in order of decreasing

size. Color coding shows the core-mantel-crust layering by density; a dashed circle represents the inner boundary of the lithosphere, defined by the strength of the rock rather than by density. The thickness of the crust and the lithosphere of Venus and Earth are exaggerated to make them visible in this figure.

Fig. 7.4: Earth’s hot interior allows the mantel to undergo convection, in which the hot rock gradually rises upward while the cool rock gradually falls. Arrows indicate the direction of flow in a portion of the mantel.

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Because S waves do not reach the side of Earth opposite an earthquake, we infer that part of Earth’s core is liquid.

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Fig. 7.5: Source of magnetic fields.

Fig. 7.6: Earth’s magnetosphere acts like a protective bubble, shielding our planet from charged particles coming from the solar wind (a wind from the Sun, composed of protons, electrons, light and heavier nuclei moving at extremely high speeds).

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Fig. 7.7: Impact process

Fig, 7.9: Volcanism. The photo shows the eruption of an active volcano on the flanks of Kilauea on the Big Island of Hawaii. The insert shows the underlying process. Molten rock collects in a “magma camber” and can erupt upward.

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Fig. 7.11: Tectonic forces can produce a wide variety of features. Mountains created by

tectonic compression and valleys or seas created by tectonic stretching are among the most common. Both images are satellite photos.

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‘Tidal Power’ is quite distinct from ‘hydro power’, which is based on the natural hydrological cycle of evaporation and rain, which flows down a mountain and harnessed by hydroelectric dams with turbines.

• It is also distinct from ocean currents produced by uneven heating of Earth and waves, produced by wind blowing over the water.

• Tidal power - or lunar power - is the result of the Moon, and to a lesser extent the Sun, causing the daily rising and falling ocean tides. These case the upstream flows an downstream ebbs (or flood tides) in river estuaries. Energy can be tapped in both directions by versatile turbines in walls Many different configurations, like walls or artificial lagoons, with high & low tides occurring twice daily.

• For barrages, the vertical difference between the water level at low tide and that at high tide is called the tidal range.

• These flows of kinetic energy can be enhanced in some locations due to the effect of concentration in narrow channels, for example between islands or other constructions, or around headlands. The physics of tidal energy

• The tides are caused by the moon’s gravitational force on Earth’s oceans.

• In any location when the Moon is above at its highest point, the tide is also highest. This results due to the fact that the Moon’s gravitational force is stronger on the near side of Earth and that the oceans, being a liquid, are free to rise slightly towards the moon.

• The Moon also acts on the whole Earth, which, because it is “solid” moves slightly towards the Moon, an leaving a budge in the oceans on the far side, which being liquid does not follow this bulk motion.

• As the Earth rotates, the bulges on both side move over the surface of the ocean.

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Fig. 7.12: A few examples of erosion on Earth.

Fig. 7.13: This diagram summarizes how different forms of light from the Sun are affected by Earth’s atmosphere.

Fig. 7.14: This diagram summarizes why the sky s blue and sunsets (and sunrises) are red.

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Fig. 7.15: The greenhouse effect. The lower atmosphere becomes warmer than it would be if it had no greenhouse gases such as water vapor, carbon dioxide, and methane.

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MORE information: • Earth is just an “insignificant” planet around an insignificant star (Sun) in a usual spiral galaxy—

• Earth is among four (4) “inner planets” that are composed of ROCK: Mercury, Venus, Earth and Mars.

• Some people consider the Moon as a terrestrial planet, and regard the Earth-Moon system as a double planet.

• Directions to Earth for space traveler: “Just head for the yellow-white star in sector 49,832 of the Orion Arm in the Milky Way, and home in on the third rock from the Sun; is a double planet and easy to spot.”

• One of a kind: Earth’s unique characteristics

• Liquid water at the surface (over 70% of the surface is covered by water)

• Plentiful amounts of oxygen in the air: 21% in composition; improbable and indicates life, according to Gaia theory; no other known planet has oxygen

• Plate tectonics (also known as continental drift): Huge moving plates that crash and form mountain, etc.

• Active volcanoes: Hot molten rock, welling up from deep below the surface---

• Life, intelligent or otherwise: only known place to have life, though Venus and mars might once have had it (as speculated by Gaia theory)

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• ENJOY THE NORTHERN LIGHTS:

• Aurora borealis (north) and aurora australius (south); glow due to streams of electrons from Earth’s magnetosphere stream down on the atmosphere below, and excite oxygen and other atoms.

• Mostly see at extreme north and south latitudes

• Range of observable extended after the peak of the Sunspot cycle.

• Next major chance = 2012-2013

• Spheres of influence: Earth’s distinct regions

• The lithosphere: The rocky regions of our planet.

• We stand on the crust, and then the mantel and the core. The core is mostly nickel and iron and is reaches about 7,000 C at the center. It has a molten region and a solid center.

• The core will get bigger as time passes and Earth cools

• Motion of liquid part causes the magnetic field – geomagnetic field that reaches far into space.

• Makes the compass needle point

• Provides a guidance system for homing pigeons, migrating birds, and ocean dwelling bacteria

• Forms the magnetosphere far above Earth

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• Shields the Earth from particles from the Solar wind and cosmic rays

• The hydrosphere: The water in the oceans, lakes, and elsewhere on Earth

• The cryosphere: The frozen regions – notably the Antarctic and Greenland ice caps.

• The atmosphere: The air from ground level on up for hundreds of miles.

• The biosphere: All the living things on Earth – on land, in the air and water, and underground.

• ALSO, Magnetosphere: protons and electrons bouncing and moving along the lines of Earth’s magnetic field from connecting North and south.

• Examining Earth’s Time, Seasons and Age

• For 4.6 billion years Earth has been rotating, while providing a natural clock, while the tilt of its axis results in the seasons, uneven heating, and much more.

• Rotates from west to east – counterclockwise – every 24 hours = mean solar time

• One year is about 365 days, one complete orbit around the Sun.

• Astronomers report observations based on Universal Time (UT), Greenwich, England.

• Tilting towards the seasons • Seasons have NOTHING to do with how far we are from the Sun!!

• We are on the same planet, and when north is summer, south is winter, and vise versa.

• Because Earth’s rotation axis is tilted by 23.5 degrees:

• Summer occurs in the north when the axis is pointing towards the Sun, which is at it highest location.

• Shines more DIRECTLY on the northern hemisphere and this more intensity;

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• The days are longer

• Vernal equinox: when the Sun crosses from below (south) the equator to “above”, experience the FIRST DAY OF SPRING

• Summer solstice: When the Sun reaches its highest point

• Autumn equinox: When the Sun crosses the equator going back down south.

• Winter solstice: when the Sun gets as far south as possible.

• Estimating Earth’s age

• By radioactivity.

• But original rock of Earth is hard to find

• So can use meteorites, which give about 34.6 billion years.

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• Making Sense of the Moon

• The moon is 2,160 miles (3,476 kilometers) in diameter, slightly less than ¼ the diameter of Earth.

• No significant atmosphere, just traces of hydrogen, helium, neon, and argon atoms.

• Solid rock

• Mass 1/81 that of Earth

• Density 3.3 time that of water.

• Getting ready to howl: Phases of the moon

• Except during a lunar eclipse, half of the moon is lit and half is in the dark

• These are the hemispheres that point toward and away from the Sun.

• And they always change as the moon moves around Earth.

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• New moon: is the beginning of monthly cycle. Near side faces away from the Sun, so is dark.

• Waxing crescent: It then becomes a crescent as it moves away from the Sun-Earth line while orbiting Earth.

• Quarter moon: When the Earth-Moon line is perpendicular to the Earth-Sun line (quarter of WHOLE)

• Waxing Gibbous.

• Full moon: when Moon is at the far side of its orbit, and opposite the Sun

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• Half of the Moon is lit up, BUT we cannot (NEVER) see it.

• WHY NO ECLIPSE OF THE SUN EVERY MONTH at NEW MOON?????

• Because the Moon’s orbit is tilted and rarely is in line with the Sun and Earth.

• WHY NO ECLIPSE OF THE MOON EVERY MONTH AT FULL MOON

• Because the Moon’s orbit is tilted and rarely is in line with the Sun and Earth

• In the shadows: Watching lunar eclipses

• During a total eclipse of the moon there is NO DIRECT Sunlight, but there is some light that is BENT around Earth, so the Moon can be seen.

• Hard rock: Viewing the moon’s geology

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Figure 2.21

The shadow cast by an object in sunlight. Sunlight is fully blocked by the umbra and partially blocked by the penumbra.

Below illustrations show the conditions for Lunar Eclipse and Solar Eclipse:

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• Asteroids meteoroids and comets of many sizes have been bombarding the Moon for billions of years.

• The moon does NOT have LARGE volcanoes, but DOES have small VOLCANIC DOMES.

• Also lava flows inside IMPACT CRATERS (MARIA).

• Moon is in SYNCHRONOUS ROTATION, so always see SAME SIDE!!

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• Quite and impact: A theory of the moon’s origin:

• Earth formed 4.6 billion years ago

• The OLDEST rocks on the Moon (radioactive) dating seem to be 4.5 billion (100 million years later)

• Giant IMPACT theory: a body 3 X that of Mars collided with Earth at a glancing angle, and scooped out material that became the Moon. Knocked into space as a vapor of hot rock, then condensed and solidified like snowflakes.

• The moon is LESS DENSE than Earth, so suspected to be made of mantel material.