Astr100 Midterm Studyguide

Lecture 13
Lunar Eclipse * An eclipse in which the moon passes into the shadow of the Earth * Umbra: the portion of the shadow that receives no direct sunlight from the light source * Penumbra: the portion of a shadow that receives direct light from only part of the light source * Eclipse season: the time of year during which a solar or lunar eclipse is possible
Types of Lunar Eclipses * Penumbral Lunar Eclipse: an eclipse where the moon passes through the earth’s penumbra, but not the umbra; last occurred 2/9/09 * Total lunar eclipse: an eclipse when the moon is completely in the earth’s umbra for a portion of the eclipse; last occurred 2/22/08 * Partial lunar eclipse: an eclipse when only a portion of the moon passes through the earth’s umbra
Solar Eclipses * An eclipse of the sun by the moon * Total Solar Eclipse: eclipse when the sun’s photosphere (or normally visible portion) is completely blocked by the moon * Corona: the outer atmosphere of the sun; only visible during a total solar eclipse * Partial Solar Eclipse: only a portion of the sun is covered by the moon * Annular Solar Eclipse: an eclipse in which the moon is located to far from the earth for the moon to completely cover the sun; the outer ring of the sun is seen as a bright ring or an annulus; occurred last 1/26/09
The interior of the earth * Average density: ratio of mass to volume; earth’s average density is 5.4g/cm^3 * Seismology: study of the earth’s physical qualities; we know the makeup of the earth’s interior by analyzing two types of waves generated by earthquakes
4 Parts of the Earth’s interior * Crust: (<100 km) thin, outermost layer of the earth; rocky and has density ~ 2.5-3g/cm^3 * Mantle: (2900km) thick, solid layer between the crust and the Earth’s core. The density of the mantle is 3-9 g/cm^3; the crust “floats” on the mantle * Outer Core: composed of liquid metals; 1800 km thick * Inner Core: innermost portion w/ density up to 13g/cm^3; composed mainly of nickel and iron * Differentiation: the chemical process responsible for the pattern that density increases inwardly; due to the sinking of denser materials toward the center of the early earth
Earth’s Magnetic Field * Magnetic Field: thought to originate in the Earth’s liquid outer core * Magnetic Axis: are not located at the poles of rotation, rather, the magnetic axis is tipper about 13degrees; magnetic poles change with time * Dynamo Effect: model that explains the earth’s and other planets’ magnetic fields as being due to electric current flowing within molten iron cores
Past and Future Reversals of the Earth’s Magnetic Polarity * Magnetized rocks of different ages have revealed that the direction/polarity of the geomagnetic field has reversed 171 times during the past 76 million yrs * Some worry more cosmic rays will hit the earth if the magnetic polarity reverses again
Earth’s Magnetosphere * Magnetosphere: the region where the geomagnetic field of Earths dominates the interplanetary magnetic field * Van Allen Belts: two doughnut shaped regions composed of charged particles from the sun captured by the Earth’s magnetic field; named after discovered James Van Allen of Iowa university who recently passed * Aurorae: patterns of different colors in the atmosphere resulting from disturbances in the earth’s magnetic field where charged particles follow the magnetic field line down into the atmosphere and collide with atoms
Lecture 14
Plate Tectonics * Alfred Wegener: credited with developing the idea of continental drift * Continental Drift: the gradual motion of the continents relative to one another * Lithosphere: comprised of the earth’s crust and mantle’s outer 40 miles; the lithosphere is broken into about 12 tectonic plates * Rift Zone: a place where tectonic plates are being pushed apart, normally by molten material being forced up out of the mantle * Mid-Atlantic Ridge: rift zone running down the spine of an undersea mountain range located halfway between America/Europe and South America/Africa; this ridge finally convinced scientists that Wegener was right
Sea Floor Spreading * Sea Floor Spreading: warm magma rises within the mantle, flows out into the ocean and cools forming a new sea floor; Africa and south America have been drifting apart for 150 mil yrs * Subduction Zone: where one sea floor plate dips into the earth and under a continental plate * Convection: plates move by convection, when magma rise moves horizontally and falls back inward at the subduction zones
Plate Tectonics * Plate Tectonics: the study of the motion of the earth’s plates across the underlying mantle; tectonic plates about 50-100km thick * Pangaea: the supercontinent believed to have existed about 250 million years ago
The Ice Ages * Climatological and geological records sshow the earth has undergone several periods of extremely cold temperatures * Milutin Milankovich: in 1920 the Serbian scientist proposed that ice ages were caused by minor changes in the obliquity of the earth’s axis and by small changes in the eccentricity of the earth’s orbit * Ice ages have occurred at intervals of 44 and 100,000 years as Milankovich’s theory, now known as the Milankovich Effect, would suggest * Radioactive Decay: the decay of uranium and other elements caused the heating of the earth’s interior over about 900 million years * Volcanic activity: occurred as a result of the heating of the earth’s core * Outgassing: the process of volcanic activity and related gases leading to the creation of earth’s atmosphere * Water vapor and steam are two of the most important gases outgassed—they went up into the early atmosphere and eventually condensed into liquid form and rained down to become oceans * CO2: second most important gas, which combined with surface rocks to create carbonate minerals * Nitrogen: third most important * Argon: fourth most important—a product of certain radioactive decays and hence its relative abundance has helped us to date the earth
The earth’s atmosphere * The density of the earth’s atmosphere decreases with increasing height * Atmosphere is composed of nitrogen 80%, oxygen 20%, minor water vapor amounts, carbon dioxide, argon, and ozone * Photosynthesis: through this process plant life created oxygen; early atmosphere likely did not contain free oxygen * Troposphere: lowest level of the earth’s atmosphere, containing ~75% of its total mass; about 11km in thickness and it's the layer in which our weather occurs * Because the troposphere receives most of its heat as infrared radiation from the ground, the temperature of it cools with increasing height * Generally, temperature decreases with increasing height * The opposite is true in the inversion layers * Ionosphere: once such inversion layer, where the upper atmosphere is being ionized by solar UV radiation * Ozone Layer: located 50 km above earth surface, this layer absorbs UV radiation; the absorption causes the temperature to peak at the height of the ozone layer; release of chlorofluorocarbons during the 20th century has reduced the amount of ozone (through molecular interactions) available to protect us
Global Warming Controversy * Infrared radiation emitted by the earth can be trapped in the earth by CO2 and other molecules; increase in CO2 and other “greenhouse gases” is linked to rising temperature * No longer a question of if global warming is occurring, but rather how severe it will be; what are the relatives roles of solar influences and mankind on global warming? Most scientists believe that mankind has the greater role
Lecture 15
The Moon’s Surface * Can be divided into maria and mountainous, cratered regions * Maria (singular mare): the lowlands of the moon and mars that resemble a sea; named this way by Galileo, who thought they we oceans * Meteorites: interplanetary chunks of matter that has struck a planet or moon; responsible for most of the moon’s craters * Earth has few remaining craters from impacts due to erosion and tectonic plate movement; on other planets where there is no protective atmosphere, eg mercury, the moon, asteroids and satellites of other planets, craters can remain intact for many years * Basalt: one of two minerals covering the surface of the moon * Lunar highlands: light in color * Lunar maria: much darker in color * Moon’s crust is 50-100km thick and thinner on the side that faces the earth * Mountains on the Moon: the result of extensive cratering over eons (not the result of tectonic activity)
History of the Moon * Radioactive dating techniques: the moon rocks brought back from Apollo astronauts have been important in forming a model of the moon’s history * Formed 4.6 billion years ago; moons surface is older than earth’s * Craters formed 3.9-4.2 billion years ago * 3.1 billion years ago: radioactive decay and molten lava caused the moon’s interior to heat for a second time; moon unchanged since then * Micrometeorites: hit the moon still, but no new crater recently
Moon’s Surface * Moons avg density is 60% of the earth’s, due to the smaller lunar mass; density of rocks on moon thought to be same as earth, but earth is denser due to overlying material inward * Weak Magnetic Field: suggests the presence of a small iron core, although unconfirmed * Weak Natural Moonquakes: occur when micrometeorites bombard the moon or when the moon is at pedigree (pedigree is moon at farthest point from earth, apogee is moon at closest)
No Permanent Lunar Atmosphere * Low Surface Gravity: no possibility of retaining a substantial atmosphere * Any early atmosphere would have evaporated * Temporary atmosphere: solar wind does knock off some sodium atoms from the lunar surface, forming a low density, temp atmosphere
Theories of the origin of the Moon * ~4.6 billion yrs ago: estimated from radioactive dating of rocks brought by Apollo mission * Double Planet Theory: 1800s theory says the earth and moon formed at the same time from the same rotating disk of material * Fission Hypothesis: Pacific ocean is where the moon was ejected from earth; doesn't explain moon’s orbit or what force could have ripped the moon from earth * Capture Theory: early 20th century, says that the moon was originally solar system debris and was captured by earth gravity; this would require a third object and the chance of this is remote * Moon has less volatile substances: more easily vaporized, maybe caused by the smaller mean density of the moon * Large Impact Theory: 1970s, says the moon was formed by an impact between a mars-sized object and the earth; the theory explains the relative compositions of the earth and moon, the orbit of the moon, and the rotation rate of the earth; has been modeled on supercomp.
Sizes and Distances in the Solar System * Diameter of sun is 109 x earth * Jupiter is 11 x earth * Pluto is 1/5 earth
Measuring distances in the Solar System * Copernicus used geometry to determine relative distances * Today we use radar
Measuring Mass and Density * The Sun contains 99.85% of the mass of the solar system
Planetary Motions * Planetary orbits are elliptical but nearly circular (except merc and pluto) * Planets revolve around sun eastward * All planets rotate counterclockwise: except for Venus, Uranus, Pluto * Inclination of Orbit: angle between plane of a planet’s orbit and the ecliptic plane; mercury is inclined at 7` and pluto at 17`
Classifying the Planets * Terrestrial and Jovial planets: all of the planets are classified into two groups other than pluto * Size, Mass, Density: jovian planets have bigger diameters, larger masses, but less dense; terrestrial planets are smaller, less massive, but denser * Satellites and Rings: 4 Jovian planets have 159 total satellites and each has a ring; 4 terrestrial have 3 satellites and no rings
Rotational Periods * Solar Day: the amount of time for sun to cross a location’s celestial meridian * Celestial meridian: an imaginary great circle that rune north to south from the north celestial pole through the observers zenith * Sidereal Day: the amount of time for passage of the vernal equinox across the meridian; one solar day is longer than a sidereal by 3.95 minutes
Lecture 16
Planetary Atmosphere * Escape Velocity: the minimum velocity an object must have to escape the gravitational pull of a planet; earth’s is 11km/s, the moon is only 2.5km/s * Gases and Escape Velocity: 1) as gas molecules interact, different molecules have different speeds 2) the avg speed of molecules depends on the temp of the gas 3) at given temperatures, less massive molecules have grater speeds than heavier ones * Temperature of a substance is defined by the avg energy of its molecules * Little free hydrogen in earth’s atmosphere because these low-mass molecules can achieve escape velocity at the temp of the upper atmosphere
Atmosphere of Planets * If a planet’s escape speed is at least 5-6 times the avg speed of molecules at the planet’s atmospheric temp, then the planet will retain an atmosphere for more than 5 billion yrs * Due to size and mass, Jovian planets have retained most of their gases
Terrestrial vs Jovian planets * Terrestrial: near the sun, small, mostly solid, low mass, slow rotation, no rings, high density, this atmosphere, few moons * Jovian: far from sun, large, liquid and gas, great mass, fast rotation, rings, low density, dense atmosphere, many moons
The Formation of the Solar System * Evolutionary and Catastrophic * A successful theory must explain: * 1) all the planets revolve around the sun in the same direction, an all planetary orbits are nearly circular * 2) all of the planets lie in nearly the same plane of revolution * 3) most rotate in the same direction except for Venus, Uranus and Pluto (VUP), which rotate retrograde * 4) the majority of planetary satellites revolve around their parent planet in the same direction as planets revolve around sun * 5) Titus and Bodes Law: a pattern of spacing among the planets as one moves out from the sun; no known physical cause * 6) planets have similar chemical composition with some differences; outer planets contain more volatile elements and are less dense than inner * 7) ALL planets and moons with a solid surface show evidence of craters * 8) ALL Jovian planets have at least one ring or ring system * 9) asteroids, comets, and meteoroids populate the system along with planets and each category of object has its own pattern of motion and location * 10) the planets have more angular momentum than the sun, even though the sun has most of the mass * 11) evidence suggests that planetary systems in various stages of development may exist around other stars * Volatile Element: a chemical element that exists in a gaseous state at low temp * Non-volatile Element: an element that is gaseous only at high temp and condenses to a liquid or solid when temp decreases
Evolutionary Formation Theories * Renee Descartes’ Whirlpool or Vortex Theory: 1644 * Immanuel Kant (1755) and Pierre Simon Laplace (1796): modifies Descartes’ vortex theory into a rotating cloud of gas that was contracting under its own gravity into a flattened disk * Conservation of Angular Momentum: states that such a rotating, contracting disk should speed up (remember the anology of the figure skater who spins more rapidly when she pulls her arms inward toward her body) * Problem with Evolutionary Theory: the sun(center of rotating cloud) should be rotating much faster; total angular momentum of planets is faster than sun, which shouldn’t occur according to Newton’s laws; lost favor in 20th cent.
Catastrophic Theories * Catastrophic Theory: the creation of the universe involves an unusual coincident such as the collision of the sun with another star; rare; recent discoveries of planetary systems orbiting other stars further discredit this theory * George Louis de Buffon: 1745, came up with first catastrophe theory that a comet pulled material from the sun to form planets; we now know comets are not massive enough to cause the breakup of the sun * Triple Star Theory: Sun, part of triple star system, gave birth to the solar system through tidal disruption; discredited once shown that material pulled from the sun would have been too hot to condense to form planets and would have dissipated
Present Evolutionary Theories of Formation * Carl von Weizsacker: eddies (aka vortices) would form in a rotating gas cloud and that the eddies nearer the center would be smaller; the eddied would condense and grow into planetsimals, which would sweep up smaller particles through collision and gravitational attraction * An object shrinking under force of gravity heats up; high temp near the protosun (newly formed sun) would have prevented the condensation of more volatile elements; planets formed near the sun would be made of non-volatile, dense material; farther out eddies would be larger and cooler so that larger planets composed of volatile elements formed * Ionized gas: as the young sun heated up gas of solar system was ionized; the sun’s magenetic field swept through the ions in the inner solar system causing them to speed up; * Magnetic Breaking: Newton’s third law says transfer of energy to the ions caused the sun to slow its rate of rotation * Stellar Wind: the flow of nuclear particles from a star; if the early sun went through stage of exhibiting strong solar wind, inner solar system would have been swept of all volatile elements; giant outer planets then would have collected these outflowing gases * Explaining other clues: over time, planetesimals likely fell onto the moons and planets causing craters; comets are likely material that coalesced in the outer solar system from the remnants of small eddies * Formation of Jupiter must have resembled that of the solar system; moons close to Jupiter are denser, moons farther out decrease in density and increase in volatility * Catastrophes may have played a minor role in our solar systems formation, but overall origin is evolutionary
Planetary Systems around Other Stars * Binary Star System: a pair of stars that are gravitationally linked so that they orbit one another * Stars with a noticeable wobble can be evidence of an unseen companion—such as a large planet or group of planets * Astromeric Method for Detecting Extra-Solar Planets: method of observing wobbles in motion of stars * Doppler Method: 1995 * Infrared Companion: such as is seen with the star T Tauri, can be evidence of possible planetary bodies * Dust Disks: provide evidence that conditions for planet formations exist around many sun-like stars * Pulsar: a compact object that emits regular radio waves; Doppler measurements have confirmed a companion orbiting a pulsar
Lecture 17
Mercury
* Hardest planet to see from earth; because planet is so close to sun, it can be seen low on the horizon just before sunrise in east or after sunset on west * Mercury has phases as does Venus * Mariner 10: flew by Mercury 1974 and returned many phtographs; mercury is covered with craters similar to the moon, but has greater gravity thus less prominent craters * Mercury cooled more slowly than the moon: thus meteors were able to penetrate mercury longer allowing lava to flow out longer and obliderated older craters, created plains between craters; mercury has smaller maria * Scarps: long cliffs seen in a line on mercury; more than the moon * Shrinking of Mercury’s crust: as planet cooled, crust shrank creating the scarps * Caloris Basin: large bulls eye crater visible from earth * No Permanent atmosphere: on Mercury confirmed by Mariner * Thin Temporary atmosphere: similar to the moon, solar wind knocks some atoms off the surface of the planet * Large iron core: is likely as mercury has surface rocks similar to earth’s * astronomers estimate that a large asteroid may have collided with mercury and blasted away most of its mantle rock * Magnetic Field 1% as strong as Earth: detected by Mariner 10 * Dynamo effect: liquid molten core moves to create electric current which creates magnetic field; mercury’s magnetic field suggests part of its metallic core must be molten * Weak Magnetic Field: is likely due to Mercury’s relatively slow rotation rate, 59 earth days
Mercury’s Motions * 88 days per orbit around sun at 48 km/s * Most eccentric orbit other than pluto * Spin Orbit Coupling: 58.65 days per rotation which is precisely 2/3 of its orbital period * Unbalanced Mass: responsible for unusual coupled rotation/revolution period * Lopsided: object that created the caloris basin was dense and its presence under the surface caused lopsidedness, leading to the spin orbit coupling * Mercury’s Solar Day: is 176 Earth days * Temp can reach 842`F, well above melting point; on the night side temp can fall to -250`F * Albedo: fraction of incident sunlight that an object reflects; radar shows a high albedo, suggesting presence of ice at poles, how it hasn't evaporated is mystery
Venus’s Motions * Sidereal orbital period of 225 days; almost circular orbit * Surface shrouded by clouds; we have been bouncing radar off it since 1961 to learn about it * Rotates Backward compared to most other rotations in the solar system * Rotation Period 243 days * Revolution Period 225 days * Solar day that is 117 earth days * Retrograde rotation: venus’s axis is tilted 177`, since greater than 90 we know it has ret. Rotation
Surface of Venus * 19 spacecraft landed since 1962 * Pioneer Venus 1 (1978) and Magellan (1990) produced radar maps of surface * Mostly rolling hills, very few highlands, many craters a few km in diameter * Surface estimated twice as old as earth’s * Past evidence of tectonic activity: mountains, large lava flows, volcanoes * Evidence of possible recent volcanic/tectonic activity * Atmospheric pressure: 90 times that of Earth’s
Lecture 18
Hypothesis for Venus/Earth Differences * Run-away Greenhouse effect was caused by higher surface temperature * Water did not condense out of the atmosphere into oceans to absorb the CO2 * CO2 remained in the atmosphere and trapped Venus’s own infrared radiation creating clouds and high temp; forewarning to earth about the effects of greenhouse gases * Earth’s temp is increased naturally by greenhouse effect; human contribution to CO2 could increase temp 5-10`F
Mars as Seen from Earth * Best seen from earth at opposition: when it is opposite the sun in our sky 55-100km; every 2.2 yrs * When Mars is seen at conjunction it is 377 mil km away
Mars’s Motions * Orbits Sun at avg 1.524 AU or 228km * Orbit more eccentric than earth * 1.88 yrs to complete orbit around sun
Mars
* Sidereal Rotational Period is 24h37m; its day is 24h40m * Equator tilted 25.2`, earth is 23.4`—almost identical obliquity * Seasons on Mars: 6 months long; greater shift in temp in southern hemisphere * Evidence of polar caps
The Martian Canal Controversy * Giovanni Schiaparelli: 1887 drawing of canali or channels on mars misinterpreted by the public to mean canals dug by intelligent life * Percival Lowell: opened observatory in AZ 1894, reported seeing many canals
Mankind’s Invasion and Its Results * Mariner spacecraft late 60s early 70s returned images ending canal speculation * Very Thin Atmosphere: about 1/200 of Earth’s; smallest atmosphere of 3 terrestrial planets * Surface: craters, volcanoes and canyons * Olympus Mons: volcano on mars twice as large as earth’s biggest; mars can grow volcanoes because it has no tectonic plates, the earth’s crustal motion would move a volcano before it can become as large as this * Thin Crust: may be responsible for the lack of tectonic plates; too thin to remain in large pieces; however Magellan radar suggests possibility of tectonic activity * Thick Crust: may lack tectonic plates because it cooled too quickly leaving the crust too thick and strong * Valles Marineris: enormous canyon on mars that stretches 4800km * Surface magnetic field indicate a striped pattern similar to that of the earth’s near Mid-atlantic ridge, meaning possible tectonic activity
Mars
* Viking probes: landed on mars in 1976 * Viking orbiters: confirmed that mars has dry riverbeds * CO2 polar caps during winter; when polar caps shrink CO2 sublimes into atmosphere * Sublime: does not melt, goes directly from solid to gas
Atmospheric and Surface conditions * Noontime can reach 20`c or 68`f; the thin atmosphere can’t hold the infrared heat and temp falls to -140`c or -220`f at night * Escape velocity: 5km/s, less than ½ earth’s * Low escape velocity and lack of ozone allowed water vapor to escape which is broken up by UV radiation; as this is broken up the hydrogen escapes and the oxygen reacts with the iron rich crust to form rust—giving mars its red color * Seasonal color changes are caused by spring winds moving the light colors top soil * Possibility has not been ruled out for life on mars
Mystery Meteorite * Meteorite found in Antarctica several years ago purportedly was knocked of from mars’ surface; controversial because some scientists claim to have discovered evidence of fossils
Lecture 19
The Moons of Mars * Two small moons: Phobos and Deimos * Both shaped like potatoes, dark, and similar to many asteroids; may be captured asteroids * Mars is most oblate terrestrial planet but still spherical, this is because all t. planets are massive enough for their gravity to shape them spherically; phobos and deimos are not massive enough, they are non-spherical like asteroids
What we have learned by exploring Mars * May tell us more about earth’s history and future * Mars pathfinder with Sojourner rover landed on July 4, 1997
Recent Martian Surface Exploration * Mars Exploration Rovers: called Spirit and Opportunity Jan. 2004, landed and both detected evidence of standing and possibly moving water during some point in the Martian past * Spirit and Opportunity: were still operational in Jan. 2011, but Spirit recently became stuck is soft soil and stopped responding to commands
Additional recent Martian discoveries * Dec. 2006 Mars Global Surveyor Spacecraft had detected evidence for current flows of water down sides of some craters * Phoenix Lander: aka Mars Polar Lander, in May 2008 discovered water ice frozen in Martian soil; also discovered perchlorates * Perchlorates: chemicals found in Martian soil which means Mars could possibly support growth of plants if oxygen rich atmosphere existed * Curiosity: aka Mars Science Lab, Aug. 2012 landed on Mars to search for evidence of conditions suitable for development of life in the past
Jupiter’s Mass * 318 x more massive than earth, 11x earth’s diameter, 1300 x earth’s volume * Jupiter has more than twice the mass of all the other planets, their moons, and asteroids combined * Jupiter’s density is only 1/3 Earth’s meaning it is composed of more light elements like hydrogen and helium than are terrestrial
Jupiter’s Motions * 5.2AU from Sun, takes 12 years to complete one orbit * revolves quickly, once every 9h50m; Jovian planets all have much quicker rotation rates * Differential Rotation: the rotation of an object where different parts have different periods of rotation; other Jovian and the Sun exhibit this * Very oblate, caused by rate of rotation
Jupiter from Space * Pioneer 10 and Pioneer 11: 10 flew within 130,000km in 1973, 11 came within 50,000 km a year later; they measured the magnetic field * Voyager 1 and 2: returned improved images of Jupiter in 1979
Jupiter’s Cloudy Atmosphere * Weather patterns last longer because surface features have little effect on Jup’s upper atmosphere unlike terrestrial planets * Great Red Spot: high pressure storm system that rotates counter clockwise with a period of 6 days, is larger than the Earth in diameter 15,000km * Giovanni Dominico Cassini who later changed name to Jean Dominique Cassini after moving to France, is 1 of 3 accredited with observing the Great Red Spot—though unknown if it was same spot; he also discovered the gap in the rings of Saturn * Samuel Schwabe: 1831, from Germany, noted the same spot we see today
Composition of Jupiter * The Galileo showed that it is about 86% hydrogen, 14% helium, small amounts of water, methane and ammonia; close in composition to Sun than Earth * Ammonia: Jupiter’s highest clouds are composed of this * Photochemical Reactions: induced by sunlight and/or lightning are responsible for the colors seen in upper atmosphere * The zones: aka light areas are high pressure regions of rising gas * The belts: aka dark areas are low pressure regions of falling gas