Earth Science - Study Guide for Exams

Here is a guide to help you focus on the important aspects of the course. Use this guide in conjunction with the Quizzes and the tools within each chapter: the Chapter Summary, Key Terms, Review Questions, etc. Study the figures (sometimes a picture is worth a thousand words, and is easier to remember). Don't save studying until the last minute! Oh, ONE OTHER THING: YOU MAY bring a hand-written (BOTH sides), 3x5-inch notecard with you to each exam!

Minerals

You should know the properties (relative masses and charges) of the three subatomic particles that make up an atom, as well as where each part is found. What are the 8 elements that make up the crust of the Earth? Can you explain what makes an ionic bond? a covalent bond? Which type of bond is likely to link the Na to Cl in the salt structure? How is one oxygen bonded to another? What do the positions A, B, C, and D tell about element "X" in the following examples: AXB ,  CXD What is the importance of, for instance, "C" in the example?

What is the definition of a mineral (all 5 parts, as discussed in class)? Be able to list at least 5 physical properties of minerals - it might be good to know what they mean, too! We talked about components of minerals - why is FeO important? [Hint: see Igneouse Rocks and Activity below!]  What is a silicon tetrahedron, and why is it important? What's the most common mineral in the crust of the Earth? What are the four important variables that control whether a mineral will form?

Rock Cycle

What is the definition of a rock? What do we look for when we describe rocks? Why is each category important? Rocks are divided into three main groups: Igneous, Sedimentary and Metamorphic. Can you briefly describe how each forms?

Igneous Rocks

There are intrusive and extrusive igneous rocks - what's the difference? You can tell them apart by the textures that we studied: Phaneritic, Aphanitic, glassy, porphyritic, vesicular. If an extrusive rock is mafic in composition (Mg- And Fe-rICh), then it is called Basalt. If an intrusive rock is felsic then it is called a Granite. Compared to Basalt, Granite is less dense and has lighter-colored, larger mineral crystals in it. See Figure 2.9, p. 45! Also, be prepared to show that you know the different rock names and what they mean (the Igneous Rock Names chart we drew in class - see slide-show handout and/or See Figure 2.8, p. 44!). See the section below regarding Igneous Activity.

When we discussed igneous rocks, we first explored what happens BEFORE the magma becomes rock ("igneous processes"). Explain why basaltic magma has a composition that is different from the mantle (peridotite) from which it is derived (hint: think about partial melting). Igneous rocks form from crystallization during cooling of magma. Bowen's Reaction Series (p. 46) is important in the process of igneous differentiation. Describe how granitic magma comes to be - how might it be related to basaltic magma (hint: think about crystal settling, also called fractional crystallization); what has to happen such that granite is eventually formed (does magma cool slowly or quickly)? Here are some things to think about: as a basaltic magma (derived from partial melting of mantle peridotite) cools, Fe- and Mg-rich minerals (olivine, pyroxene) crystallize. Because they are more dense than the surrounding magma, they may sink to the bottom, depleting the Fe and Mg content in the remaining magma. This makes the remaining magma less dense, allowing it to rise further in the Earth's crust. At lower temperatures (higher in the crust), other minerals form, and at the lowest temperatures at which magma can exist, quartz forms.


Igneous Activity

Magma erupted at the surface of the earth is called lava. The viscosity of lava is related to its TEMPERATURE, SiO2 CONTENT, and GAS CONTENT. These factors control the type of eruption (quiet or violent) and the shape of the volcano that is created.

BASALT has high temp., low SiO2 and fairly high gas content, and therefore is generally a fluid lava (not viscous). Basaltic lava flows are typically thin, and they spread out over vast areas. After many flows, the resulting shape is that of a Shield. Hawaii is an example of a shield volcano. Variations can always occur: sometimes the lava retains its gases and so flows out with a ropy texture forming on its surface (pahoehoe). Other times the basalt loses all its gases and becomes more viscous, oozing slowly out in a clinkery (rough, jagged) flow known as aa. Lavas with higher SiO2 contents are typically not as hot, and the silica may form complex molecules (polymers) in the magma, and so siliceous (felsic) lavas are more viscous (flow more slowly). When lava does not flow easily enough to allow the gases to escape, violent explosions can occur. These explosions send material (pyroclastic material: ash and blobs of lava) into the air - and these pieces cool very quickly, and then land back on the earth. This spattering can result in a cinder cone (see fig. 7.12 of your book). Cinder cones can be formed from any lava type, and are easily eroded because they consist of small, angular chunks of material that are not in equilibrium with surface conditions.

Many familiar volcanoes are composite cones (or stratovolcanoes). These form from alternating pyroclastic and fluid lava flows, and can build up into high peaks (Mt. St. Helens, Mt. Shasta, Mt. Rainier, most of the Andes, Mt. Fuji, Mt. Etna, etc.). These peaks may have craters associated with them, or they may have collapse structures known as calderas. What kinds of hazards are associated with volcanism?

Draw a simple cross-section showing the difference in the slopes developed on shield vs. composite volcanoes. Why are the slopes different? What are some of the gases that are emitted from volcanoes? Which is most abundant? What kinds of volcanoes (and what compositions) tend to occur at different plate boundaries? (Hint: reading the section on Igneous Activity and Plate Tectonics, starting on p. 213, will help to tie together many of the concepts we have been studying!)

Because volcanic material is not in equilibrium with surface conditions and often erupts under violent conditions, weathering and erosion tend to reduce the loose pieces fairly rapidly. Some of the erosional remnants of volcanoes include pipes and necks; examples are Shiprock, NM (see fig. 7.21) and Devil's Tower, WY. INTRUSIVE bodies associated with igneous activity include dikes and sills, and the magma chamber beneath a volcano may solidify into a pluton; many plutons make a batholith (fig. 7.22 and YOUR NOTES).

Weathering

Weathering involves mineralogical and textural changes at the surface of the Earth. Recall the Agents of Change: Heat, Pressure, and Fluids. Q: Why do rocks and minerals undergo weathering? A: Mostly because they were NOT formed under the conditions of the Earth's surface, so they are out of equilibrium.

Mechanical weathering simply involves a change in the size of the particles - i.e., NO change in the composition! Making large particles into smaller ones increases the amount of surface area exposed (see fig. 2.12). Here are some ways by which mechanical weathering proceeds.

Chemical weathering involves a change in the size as well as the composition of the material. It is best accomplished in the presence of water. Have you studied the reactants and products in Table 2.1 on p. 50? As an added puzzle, should you expect a relationship between the rate of weathering of certain materials and their positions on Bowen's Reaction Series? What other factors determine the rate of weathering?

Sedimentary and Metamorphic Rocks

Sedimentary rocks are those formed at or near the Earth's surface. The detrital (also known as clastic) particles can be divided (on the basis of their sizes) into gravel, sand, silt and clay; these particles  can undergo the process of lithification (compaction and/or cementation) to become conglomerates, sandstones, siltstones and shales, respectively. Detrital sedimentary rocks usually contain structures that indicate their origin, especially bedding. Chemical sedimentary rocks are derived from material that was dissolved in water. Limestone is an important chemical sedimentary rock formed from the collection of the shells of organisms, usually at the bottom of the sea. How does it differ from Chert, which is a bit less common?

Metamorphic rocks are formed deep in the Earth's crust from previously existing rocks that are subjected to changes in Pressure, Temperature and hot solutions (Fluids). Differential pressures exerted on a rock of the appropriate composition can result in foliation. Foliated rocks are divided on the basis of grain size into slate, (phyllite,) schist and gneiss. Nonfoliated rocks include quartzite, serpentinite and marble. Hey, wait - why are these nonfoliated? From what type of sedimentary rock are quartzite and marble derived? What can you tell about Serpentinite - why is it important, both historically and geologically?

Any type of rock from one of the broad groups described above (and many that are not described above!) can become any other type - i.e., an igneous rock can become the particles making up sediments, which can then become metamorphosed, etc. This is known as the Rock Cycle. The changes result from changes in Heat, Pressure, and the presence/abundance of Fluids (the Agents of Change).

Geologic Time / Scale

What is the doctrine of Uniformitarianism? What are the principles of relative dating? Perhaps you could use them to solve a geological puzzle - or at least to tell how we know that one layer is older than another. We also talked about three different kinds of Unconformities (surfaces of erosion): Angular Unconformity, Disconformity, and Nonconformity. Can you differentiate which is which? draw a picture explaining them, maybe?

What is a Fossil? What kinds of organisms make good fossils - what have they got that others don't have? One good use of the Principle of Fossil Succession is in correlation - comparing ages between rocks on different continents. This was our best method of determining ages before the advent of...

Absolute dating: a technique that is peculiar to Geology and involves natural radioactive decay. What are isotopes? What part of an atom is most significantly affected when decay occurs (the electrons, or the nucleus?) Remember, one element (parent) decays to another type of element (daughter) by a rate known as a "half-life." A half-life is the time it takes for 1/2 of the parent to decay (does not depend on the initial amount); this statistical probability does not vary with temperature or pressure, or any other variables that humans might consider. Therefore, we can date samples if we know the half-life and the amount of parent and daughter product in the sample. For example: suppose the half-life of element X is 300 years and X decays to daughter Y. Suppose you found a sample with 128 "atoms" of X and 1920 "atoms" of Y - how old is the sample?

What are the major units (Eons, Eras) of the Geologic Time Scale; what types of organisms dominated during each; and what times (ages) mark their boundaries?

Plate Tectonics

What was the basic idea of Alfred Wegener's (1880-1930) Continental Drift Hypothesis - what did he say happened, and when did events happen? What four pieces of evidence (observations) did Wegener use in his formulation of the Continental Drift Hypothesis? More importantly, HOW WAS EACH USED to show that the continents must have drifted (in other words, why does each lead one to the conclusion that the continents must have been united at one time)? Why was his theory rejected in the end?

New evidence became available (as a "silver lining" to World War II) that resulted in the hypothesis of Sea Floor Spreading. That evidence was based on Paleomagnetism. What is paleomagnetism, and why is it available for us to study it? How is it used to suggest the sea floor spreading mechanism? (Draw a cross-section of a mid-ocean ridge and explain how spreading leads to creation of the magnetic stripes on the ocean floor.) Some other evidence from the sea floor supports this idea. With increasing distance from a mid-ocean ridge: the age of basalts making up the ocean floor increases; the thickness of sediments increases; and the age of the oldest sediment (at the bottom of the pile) increases.

We can combine the Continental Drift and Sea Floor Spreading hypotheses into one unifying Plate Tectonic Theory. Plate Tectonic Theory explains much of the mountain building, seismicity and volcanism on the Earth. What are the plates made of? (See below.) There are three kinds of plate boundaries: divergent, convergent, and transform. Can you draw a really simple picture that shows what direction the plates move relative to one another in each of these three boundary types? CAN YOU GIVE A REAL-WORLD EXAMPLE OF EACH? Remember that there are two types of CRUST associated with any plate: Continental [granitic, less dense (2.7 g/cm3), thick (40 km)] and Oceanic [basaltic, more dense (3.0 g/cm3), thin (6-10 km)]. Plates can contain either or both, and this crust is coupled to the underlying Upper Mantle; together the crust and upper mantle form the Lithosphere (or lithospheric plates).

Hot spots ARE NOT EXPLAINED BY Plate Tectonics! Plate motion is thought to be driven by one of the (three) mechanisms of Mantle Convection and Gravity. On the other hand, hot-spot volcanism is deeply rooted at the core-mantle boundary, and so ignores the long-term overturning of mantle material. Hot spot volcanoes can TRACE THE PATH of the plates, however (ex: Hawaii), and so they give us more evidence of how the plates move.

How are earthquakes and volcanoes associated with these boundary types? Be prepared to draw a typical subduction zone, showing which way the subducting plate goes, and where the trench, volcanoes and earthquakes are.

The Global Ocean

Ocean features: Make sure you are familiar with the worldwide distribution of oceans (Figs. 9.1, 9.2). What is salinity, and what is the average salinity of ocean water? What are some of the major components of dissolved salts in seawater? What is salinity, and how can it change? What can change the temperature of seawater? Density is controlled by salinity (higher salinity = more dense) and temperature (higher temperature = LESS dense). More dense water will sink, less dense water will float. When the sun shines on the water, what happens to the salinity? the temperature? Is the change in density always easy to predict?

How did/do we map the features on the bottom of the ocean? Draw a cross-section of an ocean basin that has an active continental margin on one side, a passive margin on the other, and a Mid-Ocean Ridge (MOR) in the middle. Why is there a difference between an active margin and a passive one? Label the Continental Shelf, Slope and Rise, Abyssal Plain (or Ocean Floor), Mid-Ocean Ridge, and Trench. How are a seamount and a guyot related? What are turbidity currents - how do they work?

Draw a sequence of three simple diagrams explaining the evolution of a coral reef, starting with a fringing reef that evolves into a barrier reef and finally into an atoll.

What FOUR kinds of sediment are deposited on the abyssal plain? [Note that your book only lists THREE - aren't you glad you were in class to find out the fourth!?] Where do these sediments come from - what is the source of each? List examples of rock types that form from these sediments. 


Earthquakes, Earth's Interior, and Mountain Building

An earthquake occurs when the elastic limit of the rock is exceeded (elastic rebound theory). Be prepared to draw and label the relationship between a fault, the Earth's surface, the epicenter and the focus of an earthquake.

There are two basic kinds of seismic waves: Body Waves and Surface Waves. Body waves travel throughout the body of the Earth, and are subdivided into P- and S-waves. P-waves (or Primary waves) travel fastest through a given medium, and they travel by compression (push-pull in the direction of propagation). Compression is transmitted through solids and fluids (liquids and gases). S-waves (or Secondary Waves) travel slower than P-waves, by a shearing motion (side to side, perpendicular to direction of propagation - rope analogy). Shear stress is not transmitted through a fluid. Surface waves are created when P- and S-waves interact with the surface, and they travel only on the Earth's surface; they are slowest and involve the most displacement of material (which is why they can only travel along the surface), and therefore cause the most damage to structures. They travel by a rolling motion or a side-to-side motion.

How is an epicenter located? Distinguish between Mercalli intensity and Richter magnitude. How much more energy is released, and how much more displacement is there, in a magnitude 7.5 earthquake than in a 6.5? 5.5? Some hazards associated with quakes are ground shaking, liquefaction, fire (indirectly - wouldn't happen without modifications by humans, e.g., electric wires and propane lines), tsunamis, and landslides. With such damage in mind, it would be nice if we could predict them. Can we? What factors should be included in a useful prediction?

Earthquakes are used to probe the inner reaches of the Earth. What is it about seismic wave propagation that shows that the Earth's outer core is liquid? What is the Moho, and what does it represent?

There are four ways that mountains can form: by block faulting, up-warping, and folding; most of these form in an environment of compression). How does an accretionary wedge come into the picture? What are exotic terranes, and what do they contribute?

The Dynamic Ocean

Currents of the oceans are influenced by wind, the Coriolis Effect, density changes (vertical movements), and tides. What overall circulation patterns are associated with the Indian, Pacific and Atlantic Oceans?

What three factors are involved in the formation of waves? Anatomy of a wave: Crest, Trough, Wavelength, wave Height, Amplitude. Energy is passing through the water, and the rate of passage is known as the period of the wave. In deep water, the motion of water particles is circular (these are oscillatory waves) as wave energy passes through, with circles getting smaller to a depth of � the wavelength. This depth is known as the wave base. Wave base may change with the seasons, and also during a very powerful storm or when sea level changes. When the column of circular motion comes in contact with the ground (or a rock, etc.), the bottom begins losing energy to friction. Eventually (when depth is about 1/20 wavelength), the base of the column can no longer support the overlying column, and collapse occurs - the wave breaks. At this point the water carries the energy further by translation rather than by oscillation. Moving water is more capable of transporting sand particles, and so can induce abrasion and erosion.

Waves strike the beach obliquely, They are refracted around promontories (headlands), and so that is where erosional forces are concentrated. The beaches are places of deposition (note the grain size!). If erosion occurs along a beach due to removal of sediment, then that erosion causes formation of a corresponding wave-cut cliff and wave-cut platform. Because rocks have different resistances to erosion, there may also be the formation of sea stacks and arches. Deposition of sediment in areas of lower energy forms spits which may completely block the mouth of a river, resulting in a bay-mouth bar. Barrier islands can form where there is a large amount of sediment available.

Rivers are the dominant suppliers of sediment to the coast. Sediment is then carried by longshore currents. During the stormy winter months, sediment is pulled out away from the coast and gets below wave base. It is then no longer available to beaches, and so it is out of the sediment budget of the coast. Some features commonly found along coastlines with a healthy budget of sand are spits, bay-mouth bars, and tombolos. Along coastlines that are operating "in the red," groins are often erected to "trap" sediment. What does the coastline look like shortly after groins are emplaced? What happens to the rate of erosion where there are no groins? Other attempts to curb the enormous power of the oceans include breakwaters and sea walls. What's the difference between all these?

How are the coastlines affected by tectonic processes and climatic changes? What are emergent and submergent coastlines, and what features might we look for to identify them as such? What is an estuary, and what does it signify?

Why are there tides, and what are the differences among diurnal, semidiurnal and mixed patterns? When would you expect the most dramatic changes in sea level? Draw a picture indicating the reasons for Spring and Neap tides (be sure you can explain it with words, too!)

Heating the Atmosphere

Composition and Structure
Distinguish among WEATHER, SEASONS and CLIMATE.

Meteorologists measure 6 important variables to assess weather conditions: 1) air temperature, 2) humidity, 3) type/amount of cloudiness, 4) type/amount of precipitation, 5) air pressure, and 6) speed/direction of wind. Which gas is most important in controlling the weather? (Hint: it is directly involved in 3 of the above 6 variables, and indirectly in the other 3!)

What are the three most abundant gases in "dry" atmosphere? What are the properties of Aerosols, Dust, CO2, H2O, and O3 that are important to our study of the atmosphere? For example, what does ozone do for us (as inhabitants of the Earth), and why is its depletion in the stratosphere a potential problem?

You should be comfortable with the meaning of Atmospheric Pressure. Be prepared to insert the names of the layers and boundaries defined by the Temperature of the atmosphere in the proper spaces on a graph similar to Fig. 11.8 of your book! Also note how the temperature changes with altitude within each layer (the basis for the divisions to begin with) - can you explain why the temperature does that for the Troposphere and Stratosphere? (See below for more on this topic.) Make a note that air in the troposphere has a tendency to become colder with altitude - at a rate known as the Environmental Lapse Rate, which is 6.5 degrees Celsius per km, on average. All of the "weather" happens in the troposphere.

Earth-Sun Relationships
What does the angle of the sun's incoming rays have to do with heating the surface of the Earth? Why, exactly and in detail, are there seasons? You should know the following important terms "solstice" and "equinox;" you should also know WHEN they happen, and what makes them special. How is the length of day at a given latitude related to the season? Where are the Tropics of Cancer and Capricorn and the Arctic and Antarctic Circles, and why are they special?

Heat Energy and its Transfer
A strict definition: Temperature is a measure of the average energy of motion of the particles of a substance. (Particles that have lots of that energy are hot; if they have little, then they're cold. Thus a substance doesn't carry "cold" around; instead, we say it lacks energy.) That energy can be transferred in three ways: by conduction, convection , and radiation. Radiation occurs at different energy levels marked by different wavelengths of the Electromagnetic Spectrum (fig. 11.17, p. 306). Be sure you understand the 4 basic laws governing radiation (p. 307) - try explaining them to a friend! What is the average wavelength emitted by the Earth? By our star, the Sun? How about a massive blue star (use your head - stars are not in this chapter, but the principle applies)? Why are the average wavelengths of these objects different? (This is a test of your understanding of Rule #3.)

The Earth intercepts the energy emitted by the Sun. What can happen to that energy (see fig. 11.19)? What kinds of materials have high albedos? Low albedos? How exactly does the air in the troposphere (or ANY of the layers of the atmosphere) become warmed? Remember that to warm a layer, you need a heat source, a certain wavelength, and something that can absorb that wavelength - for example, the Thermosphere is heated when the Sun emits Gamma Rays that are absorbed by ions of O and N. (Can you do this for the Tropo- and Stratospheres?)

Greenhouse Effect/Global Warming

Our discussion stems from a very short but important section, which integrates other items as well. Recall from the Rules of Radiation, #4 that some materials can be SELECTIVE ABSORBERS, and important here are H2O(v) and CO2. Other principles from the section on Heat and Energy Transfer (above) also apply - in fact, explaining the Greenhouse Effect is the same as describing how the Troposphere is heated. This small section incorporates data that suggests that humans are increasing the levels of CO2 in the Atmosphere. How is this possible, and what are the consequences? 

Controls on Temperature

Factors affecting daily temperatures include the differences in four properties of Land vs. Water (hint: these are VERY IMPORTANT!), Altitude, Geography, Cloud Cover, and Albedo. Remember: "Water vapor absorbs roughly FIVE TIMES more terrestrial radiation than do ALL the other gases COMBINED." Why are winters milder and summers cooler in the southern hemisphere than they are in the northern hemisphere?

CHANCES ARE VERY SLIM that we will discuss any more about the atmosphere, except for the Coriolis Effect and Global Wind Patterns (5/e p. 359 ff) - so we probably will not get to the material in GRAY below (All of which is referenced to the 4th edition of the text) ... :-(

Clouds and Precipitation

Now is the time for us to grasp further the importance of phase changes of water. See fig. 12.1 (and note that some of the numbers are not correct, as discussed in class, but that's no big deal). The release and absorption of heat are important in our understanding of the driving mechanism of clouds and storms, and also of the formation of precipitation. Water vapor is dissolved in air. Given temperature and relative humidity of a parcel of air and a chart similar to Table 12.1 (p. 312), could you calculate the dew point? What's so important about the dew point, anyway? (You may find parts of the answer below...)

Recite the following mantra: "Rising air cools, and cool air holds less water than warm air." A parcel of air cools as it rises because it "does work against" gravity, and because of expansion (i.e. it pushes out on the surrounding air). What are the Dry Adiabatic Rate (10oC/km) and the Wet Adiabatic Rate (5-9oC/km)? How come the Environmental Lapse Rate is not the same as either of these? Air can be FORCED to rise - an important reason for the formation of Rainshadow Deserts. What causes forced lifting of air? (Hint: 3 causes are discussed in your book.)

As moist air rises, for whatever reason, condensation occurs when the air temperature reaches the dew point. At temperatures below the dew point, clouds form. The altitude and rate at which they form control what kind of cloud forms. We will be discussing Stability, Instability, and Cloud Types! Which clouds form where? Suppose, just suppose, I were to show you some pictures of clouds. Could you identify them? Fog is another kind of cloud, but doesn't have to form by rising - after all, it's on the ground! What are some of the ways that fog forms - particulary advection fog?

Air Pressure and Wind

Air pressure is the weight of the overlying air per unit area. Air tries to flow from High pressure (areas where air molecules are concentrated, or moving downward) to Low pressure (areas where air molecules are less concentrated because air is rising). Take a GOOD, LONG LOOK at the pictures that refer to the Coriolis Effect and the General Circulation of the Atmosphere. We will also study Land and Sea Breezes, and the Santa Ana Winds!!

Weather Patterns and Severe Storms

Air that is moving slowly near the Earth's surface tends to try to equilibrate with that surface. When this occurs over a broad region, we can see that an air mass forms - a huge volume of air that has generally the same characteristics (especially concerning TEMPERATURE and MOISTURE) throughout. Thus we can divide broad areas of the Earth into source areas for these air masses that include Polar (cold), Tropical (warm), continental (dry) and maritime (wet) (see fig. 14.2!). However, remember that we have global circulation cells that eventually force the air to move from one region to another (or does the Earth move under the air?). This sets up a series of battle lines, or fronts, where warm air rides up over cool air (warm front), or colder air, being more dense, displaces warmer air by pushing it upward (cold front). These two kinds of fronts develop characteristic shapes, as shown in figs. 14.4 and 14.5. What progression of clouds would you expect to see during the passage of an ideal warm front? a cold front?

Explain or describe the life cycle of a middle-latitude cyclone - how does it start, and how does it develop? Which way does the air circulate, and which front moves faster? (If you grasp that, could you draw cross-sections such as those in fig. 14.6/7? If you can do that, then you can answer the bold question toward the end of the previous paragraph.) The jet stream can help maintain a system of high or low pressure so that it does not fizzle out (fig. 14.9).

What are the three stages of development of a Thunderstorm, and what happens at each stage? (see Fig. 14.3 and pp. 364-7).

Earth's Place in the Universe

How did Eratosthenes determine the spherical Earth's diameter in about 280 B.C.? We feel rather a sense of stability as we stand in one place on the surface of the Earth. Thus it makes sense that the Universe revolves around us (as in Ptolemy's geocentric theory). Today we know the Earth is moving; what do the terms rotation, revolution, and precession mean? (We mentioned these in a previous chapter on Weather.) As Copernicus started to tell us, the Earth (and all the planets) revolves about the Sun (heliocentric theory) along what we know today to be an elliptical path. Its rotational axis is tilted relative to the plane of the ecliptic. Tycho Brahe spent years making a huge number of measurements (using stellar parallax, see below) of the motions of the planets. Johannes Kepler used this data to develop his Laws of Planetary Motion:

1. Planets move in elliptical orbits, with the Sun located at one focus.

2. The line between a planet and the Sun "sweeps out" equal areas over equal periods of time (indicating that the velocity of the planet varies with its position in its orbit). What are perihelion and aphelion?

3. The orbital periods of the planets and their distances to the Sun are proportional, or P2 / d3 = a constant (this formula is sometimes written another way: P2 = a3, where a has the same meaning as d). This relates the time of a planet's orbit IN EARTH YEARS to its distance from the Sun IN A.U.!

What 5 important discoveries were made by Galileo Galilei? Sir Isaac Newton (and a well-deserved title he has) formulated the Universal law of Gravitation (see above), among other contributions.

What are the three important motions of the Earth? Be sure you can identify the phases of the moon, and that you know WHY these phases progress the way they do (complicated!). What are lunar and solar eclipses (which is which)?

Touring Our Solar System

Components of the solar system include the Sun, planets, meteoroids, asteroids and comets, among other things. Can you name the nine planets, in order, from the Sun outward? Could you name which planet, or identify an object as a meteoroid, asteroid, or comet from a picture? We can divide the planets into two groups (Terrestrial and Jovian) based on their characteristics, especially their size, density, and atmospheric and bulk compositions. Terrestrial planets are small and made of dense (4-5.5 g/cm3) rocky (silicate) materials with little or no atmospheres, while Jovian planets are large and have densities less than 2 g/cm3. They are composed of gases of H and He and ices of methane, ammonia, carbon dioxide, water, etc. and may have small rocky cores. Craters on the surface of rocky planets and satellites indicate a relative age for that surface - i.e., highly cratered terrains are older than lightly cratered areas.

Other components: Identify the different features of a comet at its closest approach to the Sun (perihelion). Which way does the tail point - and WHY? Comets are thought to originate in the Oort cloud. Where is the Asteroid Belt? WHY do asteroids occur there?

Beyond Our Solar System

Astronomy deals with huge quantities, such as vast distances and enormous spans of time. It is therefore essential to gain an understanding of the "astronomical" (sorry, I couldn't resist :-) units involved. What is an Astronomical Unit (A.U.)? a light-year? a parsec (pc)? (Remember that we use parallax to define a parsec.) We use these units to measure 1) distance to stars/objects, and 2) size of galaxies and superclusters. We can also determine the mass, brightness (relative vs. absolute magnitude) and temperature of stars. These measurements indicate that there are different kinds of stars; they are plotted on the "H-R" diagram. What kinds of stars are out there, and where do they plot on the H-R diagram? (See fig. 16.5, p. 420)

The closest star is our Sun. What powers the Sun - in other words, from where does it derive all its energy to warm us? Can you describe/draw a picture outlining the evolutionary process of a low-mass star such as the Sun? (Hint: see H-R diagram) What might happen to a star with a different mass from our Sun? Stellar processes are responsible for creation of the elements of the Periodic Table. As a general rule, the more common the process, the more abundant the element. The first stage of nuclear fusion is commonly known as Hydrogen Burning. What is the product of this reaction? What other elements can be created by fusion reactions within stars? Many elements that we can find within the Earth (especially those heavier than iron) cannot be created by these fusion reactions. Where are the conditions of pressure and temperature high enough to create the other elements on the Periodic Table?

What other kinds of objects are out there? Black holes, neutron stars, white dwarfs (dwarves?), nebulas, clusters. What are the four basic kinds of galaxies? In which galaxy are we, and what kind is it? Galaxies aren't the biggest "things" out there - there are also galactic clusters. Which is ours? WHAT'S HAPPENING TO OUR UNIVERSE??? (Don't get too excited - we're only concerned here with whether it is expanding or not, and how we know this...) Whoa...

 


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