Updated: 18 April 2005 Monday.
Modified: 11 April 2007 Wednesday.
Monday 4/18, Tuesday 4/19: OFFICE HOURS 10am-3pm.
Wednesday 4/20: PHYS-104 Final Exam (2 hours) 8am-10am, 1104 Rood Hall
Thursday 4/21: Dr. Phil may not drive in today -- if you have to make up the Final Exam, please contact Dr. Phil ASAP
Friday 4/22: OFFICE HOURS 10am-3pm. Last chance to make-up Final Exam before a Zero or Incomplete.
Wednesday 1/5: Class begins. Nova on PBS Tuesday night -- Discussing the missions of the two Mars rovers, Spirit and Opportunity, still operating after a year on the Martian surface. Located half a world apart, so only one at a time is in Martian daylight and running. Martian sol (its day) is 24 hours 40 minutes long and the teams working the rovers are working on Martian time, not Earth time. What is the significance of the "blueberries" found by Opportunity? They are hematite nodules and are eroded from layered, not volcanic rock. Hematite on Earth is formed by iron leached from rock by water, and layered rocks on Earth are formed by sedimentary processes. Both of these suggest liquid water once was on the surface of Mars. And if there is/was water, then possibility there was/is life on Mars increases. Exciting times, even for our local neighborhood.
Friday 1/7: What do we see in the daytime sky? The Sun, clouds, fog, birds/planes/flying objects, smoke, dust/dirt/sand, rain/snow... and BLUE. Why is the sky blue? "Because it's not green," will satisfy a small child for a few seconds. What we call white light is the distribution of light wavelengths from Red to Violet (ROYGBIV) that we can see in sunlight. Dust and water vapor in the atmosphere can scatter blue light (it's the "right size"). The scattered blue light bounces around and appears to come from everywhere, hence the blue sky. At sunrise/sunset, the sunlight has to go through more of the atmosphere, scattering more blue light and making sunlight appear reddish in color, because we're removing the blue. The evening/night sky can still look blue to a camera taking a long exposure, long after we would call it black. In 1976, the Viking I landed on Mars. The first color photographs released by NASA showed a red planet with a blue sky. Later, when they corrected the color, the Martian sky ended up a pale salmon color instead. Different planet, different atmosphere. Light pollution caused by our use of outdoor lighting makes it harder to see the night sky. Light travels at 186,000 miles/sec. The Moon is 250,000 miles away -- it takes light about a second and a half to get there -- three seconds round trip. You can almost have a conversation. The Sun is 8 light minutes away. But light might take 15 minutes to get to Mars (except right now when it is really close) and the Outer Planets are even further away. And this is just still in our neighborhood. The Light Year: How far light travels in a year. The nearest star is over 4 light years away! Distribute syllabus. Q1 - Attendance and choosing a PID (Personal ID number).
Monday 1/10: Nighttime: why is the sky black? What does one see? Moon, Planets, Stars, Comets, Meteors/Meteorites. Other than the stars, most of these are "local" -- within our Solar System. Discussion of size. Miles. Kilometers (km). The Astronomical Unit: 1 AU = 93 million miles = orbital radius of Earth's orbit. The speed of light, c = 186,000 miles/sec = 300,000,000 meter/sec = 300,000 km/sec
Wednesday 1/12: What shape is the sky? Bowl shape is something of an optical illusion. How do we know the Earth is round? Sailing ships don't just get smaller as they sail away, their hulls disappear first and then the sails as they go over the horizon. And Earth's shadow on Moon during Lunar Eclipse. Distribute Topic 1 Movielist assignment (downloadable PDF file).
Friday 1/14: Discussion of History in the Making -- Huygens Probe just landed on Titan, a moon of Saturn, at classtime -- awaiting first pictures. So Quiz 2 is an assignment on learning something about these new observations. Solar System is a few billion miles across - a few light-hours. Nearest star is 4.4 light-years (LY). Milky Way galaxy is 100,000 LY across and contains 100,000,000,000 stars. Observable universe seems to contain 100,000,000,000 galaxies and is huge. Looking into space is Looking back in time, since it takes time for light to travel from there to here. Universe is expanding. Everywhere we look, most of the galaxies are headed away from us. (This does not mean we are at the Center of the Universe!) "Run the film backwards" and everything collapses to a single point in time -- The Big Bang. How do we know? Red shift / blue shift of light due to Doppler Shift. Example of train horn approaching and then receding -- change of pitch of sound. Doppler radar for cops and weathermen. Same effect with light. Things traveling away from us have white light shifted towards red. Furthest galaxies are the oldest. Traveling away from us at near the speed of light!
Monday 1/17: Dr. Martin Luther King, Jr. memorial observance [No Class Today]
Wednesday 1/19: How do we know what we know about objects in space? (1) Remote Viewing (telescopes and other sensors from Earth or near Earth). (2) Local Viewing (sending probes in the neighborhood -- all the planets except Pluto). (3) Direct Contact (probes landing or making contact -- only a few places). Viewing is through light -- all kinds. Visable Light. The colors of the rainbow: ROYGBIV (Red Orange Yellow Green Blue Indigo Violet). Is Light a particle? Or is light a wave? Wave-Particle Duality says that it's both, but it was a big fight between 19th century physicists before they understood this. As a wave, light has both a wavelength (lamda, the repeat distance) and a frequency (f, how often it repeats in a second). As a particle, light is called a photon. The energy of a single photon is E = h f (Energy = Planck's constant times frequency; Planck's constant is a fundamental constant of our universe.). The Electromagnetic Spectrum. Put ROYGBIV visible light in the middle. As one goes past red, the wavelengths get longer and the frequencies get lower. IR -- infrared light, which we feel as heat. When you hold your hand out in sunlight, it isn't the visible light that feels warm, it's the IR part of sunlight. Microwaves -- including the microwaves in your microwave oven, have a wavelength in the centimeter range. Radio waves -- wavelengths get longer, going into the meter range. Includes the frequencies used by AM and FM radio. TV currently uses two radio frequencies, one for the audio and one for the picture. There is currently a plan to change U.S. television over to a digital HDTV system in a few years, which uses higher frequency radio waves, leaving the old TV channels available for new police and fire department radios. Finally there is ELF -- Extremely Low Frequency, extremely long wavelength radiation. Developed by the U.S. Navy to communicate with submarines in the deep, ELF waves have a wavelength up to miles long.
Friday 1/21: On the other hand, as one goes beyond violet, the wavelengths get shorter and the frequencies get higher. UV -- ultraviolet light, including UV-A and UV-B, the light that causes tanning and skin cancers. X-rays -- more penetrating radiation, useful to look inside things, but Superman's X-ray vision is impractical. Gamma-rays -- even more dangerous and penetrating radiation, photons are much more particle-like than wave-like. They come from nuclear reactions inside the nucleus of atoms.
Monday 1/24: Two views: (1) The Earth surrounded by the Celestial Sphere and (2) an observer standing on a flat surface surrounded by the Celestial Sphere. The second view will vary depending on where on the Earth you are standing. Half the Earth is lit by the sun and half is in shadow between sunrise and sunset. Thinking about Local view: horizon line, straight up is Zenith. Celestial Sphere -- "most" bright sky objects fixed on the Celestial Sphere, which appears to rotate on the axis through the Celestial North/South Poles. The sun, moon, planets, comets, asteroids, etc. are not "fixed" on the Celestial Sphere. The sun follows a path 23½° to the equator called the Ecliptic, which is responsible for the seasons. The angle of the Ecliptic to the horizon, at sunrise in the East and sunset in the West. Latitude (angle north or south of equator). Equator is 0°. Topic of Cancer and Tropic of Capricorn are ±23½° from the Equator. Arctic Circle and Antarctic Circle show lands with 24-hour sun in summer and 24-hour dark in winter. Longitude (angle east or west of Prime Meridian, which goes through Greenwich, England). Local time: sunrise, sunset, noon. Standard time: allows clocks to keep same time over a large geographic area -- time zones. If we give the equitorial position on the Celestial Sphere in hours, then 360° ÷24 hours = 15° per hour. Almanac tables give adjustments for days and location.
Wednesday 1/26: An alignment of planets, 5 March 1953 BC, appears to be the Year One start of the old Chinese calendar. The development of astronomical tables and solar system models, long before computers, has allowed people to calculate position, lunar phases, eclipses, and events (interesting coincidences) in the night sky. In 2004 the Transit of Venus allowed astronomers to witness the planet venus passing in front of the Sun. (In the words of Brother Guy, Vatican Astronomer, "This is cool!" Asked what the scientific significance of observing the Transit of Venus, Brother Guy told the reporter, "Well, this is cool!" And so it is.. grin.) The last Transit of Venus resulted in many amateur astronomers going to great lengths to view, see or photograph the event -- and John Phillip Sousa wrote a Transit of Venus March. Really. In a more serious vein, the development of a sound theory of the solar system and the night sky means that we can anticipate events and understand why they occur -- and not be frightened when strange things appear in the heavens above and superstitious people have to worry about what they did wrong to make the sun disappear, the moon to appear dark and red, or the bright wandering planets to all gather in the same morning sky. The Chinese survived 5 March 1953 BC, and so started the calendar at the Year One, commorating their rebirth because they had survived and were therefore worthy.
Friday 1/28: The majority of the Solar System falls in The Plane of the Ecliptic. Mercury & Venus: The Morning Star and The Evening Star. The angle of the Ecliptic to the horizon, at sunrise in the East and sunset in the West. (Reversed Down Under in the Southern Hemisphere.) Life on Earth dominated by three natural cycles. The 24-hour day due to the rotation of the Earth on its axis. The 365 day year due to the Earth's orbit about the Sun. Finally, we get the approximately one-month cycle of the Moon orbiting the Earth. Phases of the Moon as seen from the Earth. The Moon, when visible, provides light for work and travel. The lunar day, or time to rotate on its axis, is the same as the sidereal period, so we primarily see just one face of the Moon. (The fact that the Moon's orbit is not quite circular and is tilted, allows us to see about 59% of the Moon's surface over time.) The far side of the Moon was not seen until a Soviet spacecraft with a camera went past the Moon in 1959 and sent back pictures. This is NOT "the dark side of the Moon", because the far side of the Moon gets day and night from the Sun just the same as the near side. Solar eclipses occur when the New Moon actually passes in front of the Sun. A total solar eclipse blocks the bright disk of the Sun complete -- the apparent size of the Moon is roughly equivalent to the apparent size of the Sun. An annular eclipse occurs when the Moon is a little further away and does not completely cover the Sun, leaving a bright ring. Eventually, all solar eclipses will become annual, as the Moon slowly moves away from the Earth. Tides: High and Low (oceans more or less attracted by Moon's Gravity). Combination effects of Moon and Sun on the Tides: Spring tides (unusually large high tides, low low tides), Neap tides (lower high tides and higher low tides). The Sun may be bigger and have more gravitational force on the Earth than the Moon, but the change in the force as a result of going from one side of the Earth to the other as a 1/r² law, means that the Moon has a bigger effect on the tides than the Sun. Discussion of Lunar Calendars versus Solar Calendars. Q3/4 Take-Home, due Wednesday 2 February 2005.
Monday 1/31: "We can always make the world more complicated." In fact, we start out by simplifying everything so we can get at the underlying Physics. But the real world is messier. The problem is that "everything happens at once". So we had the high tide lining up with the Moon's gravity and the Earth turning underneath the tidal bulges. Then we added in the effect of the Sun's gravity. But friction between the Earth turning and the tidal bulge pushes the tidal bulge slightly off-line from directly towards the Moon. (And this friction is slowly slowing down the Earth's rotation -- the day was only 18 hours long nearly a billion years ago.) Newton's Law of Universal Gravity provides the force that keeps the planets orbiting the Sun. It is a 1/r² law, because it inversely depends on the square of the distance between the centers of the object. It also involves two masses, because it is the interaction of mass-1 with mass-2 which provides the gravitational attraction. Weight is not equal to mass. Mass is a measure of how much "stuff" a matter object contains (and yes, "stuff" is a technical Physics term). Weight is a measure of the force of gravity on the object. So how can Meijer's sell a can of peas which says Net.Wt. 16 oz = 1 lb. = 454 grams? Because on the surface of the Earth, 1 kilogram of mass corresponds to 2.2 lbs. of weight. And Meijer's has only ever sold cans of peas on the Earth. Textbook Appendices and Glossary. Good stuff here! Page A-15, Table E-2 is very useful on current Take-Home Quiz 3/4 assignment.
Wednesday 2/2: Near and far: Most orbits are not truly circular, but elliptical. A circle is a special case of an ellipse with a constant radius. An ellipse is an elongated circle with a major axis and a minor axis. From the center, we can measure the "Semi-Major Axis" and the "Semi-Minor Axis". For something in orbit about the Earth, the distance of closest approach is perigee. The distance of furtherest approach is apogee. (For orbits around the Sun, these are perhelion and aphelion respectively.) If a Solar Eclipse happens at perigee for the Moon, then it may be possible to have a Total Solar Eclipse. If the eclipse happens at apogee for the Moon, then it may be possible to have an Annular Eclipse. How bright is something? Depends on distance (1/r² law again). If emitting light, like a star, depends on size, type, age. If reflecting light, like a planet, moon or gas cloud, depends on size and albedo. Albedo is a measurement of the reflectance -- how much of the light which falls on an object gets reflected back to space. Moon has a low albedo. So Full Moon at night is not nearly as bright as Full Sun at day, because Moon is a reflector not a source of light, and not a very good reflector either. Sometimes near a New Moon, we can see a bright thin crescent moon, but also the outline of the rest of the Moon -- this is because the day side of Earth is facing the Moon, so this is reflected "Earthshine." Thought Question: If one looks up in the sky and sees the Moon, what does someone on the Moon see when looking back at the Earth? (Earth goes through phases, but roughly remains in same part of the sky. The famous Apollo 8 video of "Earthrise" was taken in lunar orbit and the Earth "rose" because they were going around the Moon.) Apparent Magnitude (as seen from Earth), Absolute Magnitude (as seen from a Standard Distance). Old form: visible stars ranked first class (brightest) through sixth class (dimmest) stars. New form: visible stars are magnitude 6 and brighter. Most stars in the galaxy are small dim ones, which we mostly don't see. Further discussion of the take-home quiz 3/4, extending due date to Monday 7 February 2005. Solution to Sample Exam 1 is given on the class webpage.
Friday 2/4: Exam 1 re-scheduled for here.
Monday 2/7: Models of the Universe eventually became Models of the Solar System as we began to understand just how big the Universe is. Early Man would certainly have felt as if the Earth was the Center of the Universe (geocentric). But the Sun is very bright and powerful, and it is also possible to construct models where the Sun is the Center of the Universe (heliocentric). One could also suggest which objects in the sky were nearer and which were farther. The BIG stumbling block was that some of the planets, most especially Mars, exhibited this bizarre retrograde motion, whereby the seem over the course of some nights to slow down, stop, turn around, go backwards against the fixed stars, then resume the normal progress through the stars. The Greeks weren't nearly as dumb as some modern textbooks make them out to be. Pythagoras (he of the right triangle and the Pythagorean Theorem, a² + b² = c²) and Aristotle both were able to show that the Earth was round and not flat. Aristarchus argued for a heliocentric model around 400 B.C. On the one hand, it roughly predicted the retrograde motion of Mars. But it also suggested stellar parallex, which turns out to be too small for the Greeks to have measured. It was Ptolemy in the early The real problem with the models was that the Greeks and their intellectual descendents were very fond of the perfect geometric shapes and solids. So orbits which are perfect circles are to be preferred, especially as one ascends into the more perfect heavens.
Wednesday 2/9: Often the major solar system models are broken into 3 categories: Ptolemy (geocentric), Copernicus (heliocentric) and Kepler (heliocentric with ellipitical orbits). But there are more systems, and each offered some improvements. (Aristarchus, Aristotle, Ptolemy, Copernicus and Kepler.) Ptolemy versus Copernicus -- geocentric versus heliocentric. The concept of elegance and beauty in scientific theories. Perfectly circular orbits (needing epicycles) versus elliptical orbits. William of Occaam, 14th century. Occaam's Razor: "It is vain to ask Nature to do with more, that which can be done with less." (Used by engineers as the KISS Principle -- Keep It Simple, Stupid.) Just as the heliocentric model replaces the geocentric model, ellipses supplant the circles & epicycles. Now we have one continuous curve at work and all the planetary orbits are treated the same. Tycho Brahe's astronomical observations and data, Kepler making it work.
Friday 2/11: Kepler's Three Laws of Orbits: (1) All planetary orbits are ellipses with the Sun at one focus. (2) Equal Area Rule -- The time it takes to sweep out an arc length 1 that subtends an area 1, is the same time as another arc length 2 that subtends an area 2 = area 1. This tells us that when planets are closer to the Sun, they are faster (fastest at perihelion) and when they are farther way, they are slower (slowest at aphelion). (3) The Period Rule. T² = a³.For the orbits about any given body, the square of the period (T or p, in years) is proportional to the cube of the radius (use average radius a in AU). Question: What is Accuracy? What is Precision? (Or Precise vs. Accurate) Q5 Take-Home, due Wednesday 16 February 2005.
Monday 2/14: Return X1. Go over exam. Ptolemy to Copernicus to Kepler. In trying to determine the scientific truth, we see one path which goes from Observation to Data to Empirical Formula. (Experimental/Observational) Another path looks to develop from First Priniciples of Physics (ab initio in Latin) to Theories/Equations/Laws. (Theoretical) A third path uses Numerical Methods and Computation to build computer models and simulations and test/measure things which cannot be done in the lab. Example: Starting from a dust cloud or debris field of such a size, composition and rotation, using only gravity and collisions, and let it run for hundreds of years to billions to see what one gets. Example: Problems of computer weather forecasting.
Wednesday 2/16: Although Kepler's model uses elliptical and not purely circular orbits, most planetary orbits are "fairly" circular. So let's consider some of the physics that is at play. Newton's Law of Universal Gravity provides the force that keeps the planets orbiting the Sun. For an object traveling in a circle, the velocity is tangent to the circle, while the centripetal acceleration points towards the center of the circle. We can use the equations for Uniform Circular Motion (UCM), combined with Universal Gravity to try to find the period T, to make one orbit. Newton's Three Laws of Motion: First Law - An object in motion tends to stay in motion, or an object at rest tends to stay at rest, unless acted upon by a net external force. Second Law - F=ma. Third Law - For every action, there is an equal and opposite reaction, acting on the other body. (Forces come in pairs, not apples.).
Friday 2/18: But Kepler's orbits are elliptical. His Equal Area law tells us that a solar system body (planet, comet, asteroid, etc.) will be moving faster at perihelion and slower at aphelion. At those two points, perihelion and aphelion, the gravitational force from the Sun is radial inward and perpendicular to the velocity -- exactly as in UCM. However, at other points along the ellipse, the gravitation force from the Sun will point at the Sun and is not perpendicular, so coming in from aphelion, the planet will be accelerated and speed up. After perihelion, the Sun's gravity will work to slow down the planet. So Kepler's Equal Area law has a basis for existing. The more elliptical (eccentric) an orbit it, the longer it spends near aphelion. Most comets spend nearly all their lives near aphelion, diving down around the Sun and back only for brief periods of time. Sedna is a Kuiper Belt object, past Pluto. Perihelion is around 75 AU, aphelion around 1000 AU. We observed it because it was near. The Oort Cloud is suggested to be a spherical shell around the Solar System, which is otherwise more of a flattened disk, and we observe about one comet a year coming in from any direction, with a calculated orbital period of ~ 1 million years, which suggests there are at least a million comets out in the Oort Cloud. Quiz 6 Take-Home, due Wednesday 23 February 2005. (Solution to Q5 which is useful!)
Monday 2/21: The Milankovich hypothesis: The Earth's weather will vary over time as a result of the confluence of three different variations in the Earth-Sun system over time. (1) The shape of the Earth's orbit varies over a 100,000 year cycle. Right now about ±1.7% from true circular orbit. (2) Precession of the spinning Earth (the slow circular "wobble" of a spinning top) changes the direction the Earth's axis points over a 26,000 year cycle. (3) The orbital inclination (angle between the Earth's axis and the solar system axis) varies between 22° and 24° over a 41,000 year cycle (currently it is 23½°). Discussion on Global Warming and the problems of detecting whether we have it today. News media can't make up their mind if we are heating up or ready to have the next Ice Age -- you can't use short-term local data. Evidence supporting Milankovich. Core samples. The Wisconsin Desert. Example: temperature data for cities only goes back so far.
Wednesday 2/23: Exam 2.
Friday 2/25: <Spirit Day> No classes. Effective start to Spring Break.
Monday 2/28 to Friday 3/4: WMU Spring Break. No classes.
Monday 3/7: Our Sun. A completely average and boring, ordinary star -- and a good thing, too. And most of our neighboring stars are also not all that exciting either -- also a good thing. It's radius is 697,000 km or 109 times the radius of Earth. That makes it just under a million miles in diameter. But the volume of the Sun is 109³ times as big or 1,295,000 times the volume of the Earth. Technically, our Sun is a Class G2 star, Luminosity Class V. Stars with Luminosity Classes I-IV are brighter, but more unstable. The surface of the sun corresponds to a temperature of 5800 Kelvins, which we think of as our friendly, bright yellow sun. The basic classification of stars O B A F G K M covers bright blue Class O stars at 40,000 Kelvins, down to small, red Class M stars at 3500 Kelvins. (Temperature Scales: °F, °C and K (Kelvins). In the U.S. we mainly use the Fahrenheit scale, while most of the world uses Centigrade/Celsius. However in many Physics equations, it isn't good to have zero or negative temperatures, so the Kelvin scale is an Absolute Temperature scale. Absolute Zero is the coldest possible temperature.) If the Sun were a little cooler, it would be a little redder and have less harmful UV light, but otherwise it's good to have a G2 star. You can't really look at the Sun directly, except under special circumstances. If you try, you should trigger the Sun-eye-blink reflex and either blink or sneeze. By the 1800s, astronomers and physicists had a good idea of the size of the Sun and came up with an intriguing mechanism to explain how it glows -- gravitational contraction causes the Sun to shrink because the gas is slowly being pulled it. This mechanism would light the Sun for about 25,000,000 years. Sounds impressive, but in the 20th century we learned the Earth is billions of years old. It takes nuclear physics to explain how the Sun works. The light from the Sun originates in the core -- intense pressures heat the core to a temperature of millions of degrees, to where atoms can fuse together in nuclear reactions to form new atoms.
Wednesday 3/9: The structure of the sun: central core (15,000,000 K), photosphere (bright, 5800 K), thin chromosphere above (dimmer, 10,000 K, source of UV light), high temperature thin corona away from surface (1,000,000 Kelvin, source of X-rays). Solar winds carry small fraction of mass away at speeds up to 1000 km/hour, but still 10,000,000 tons/year. Sunspots appear to be dark blemishes on the surface of the sun, but the material we're seeing is still quite bright -- just not as bright as the surrounding surface. Sunspots are magnetic effects -- they come in pairs. The leading spot is a North magnetic pole and the trailing is a South. The light from the Sun originates in the core but the radiation can't get straight out -- it gets absorbed, reflected, re-radiated at lower frequencies. Eventually, after over a million years, the light finally reaches the surface, where it takes just eight minutes to cross space to the Earth. (Hans Bethe dead at 98. He received the 1967 Nobel Prize in Physics for coming up with a method of fusion inside stars.) The sun has burned for billions of years. How do we know if it's still good for a while? Thermonuclear fusion produces neutrinos (named by Enrico Fermi, neutrino means "little neutral one" in Italian). These neutrons come straight out of the Sun at nearly the speed of light, unlike the light we see, and we can detect them on Earth. So we know that fusion is still going on strong in the core of the Sun, which means we get light for "at least" another million years (grin). The formation of our Solar System. Second Generation star system -- otherwise there'd only be hydrogen. Death throes of some large stars throws off higher elements. Gravitational attraction of interstellar dust cloud. Any sense of rotation is exagerated by the Conservation of Angular Momentum -- the rotational speed goes up as the radius gets smaller. Do we have the only solar system with planets? No. Though to be fair, (1) we cannot see any planets around other stars directly, just as we cannot resolve any distant star into a disk in a telescope -- they are too far -- and (2) those planets we detect by indirect means must be very large, very strange planets.If the Sun's output varies over time, how does that affect our climate? Describe computer study during Dr. Phil's college days trying to determine if Earth is maintaing, gaining or losing temperature over the long term.
Friday 3/11: Return X2 and go over it. NOTE: The original date for Exam 3 is inconvient to many and therefore, the class agreed to move Exam 3 from Friday 25 March 2005 to Wednesday 30 March 2005. This does not change the amount of material which will be covered by Exam 3. Q7 Take-Home, due Wednesday 16 March 2005 (has the wrong date on the quiz).
Monday 3/14: The 11-year sunspot cycle. (Can be as short as 7 years or as long as 15 years.) British astronomer Maunder. (1) The Maunder Butterfly -- At the beginning of each sunspot cycle, the sunspots appear in the mid-lattitudes. By the end of the cycle, they are close to the equator. (see text p. 272?) The "butterfly" is what the graph of Lattitude vs. time looks like. (2) The Maunder Minimum -- noted that there were relatively few sunspots from 1645 to 1715, which corresponds to "The Little Ice Age" in Europe -- a period of slightly lower solar output. The sunspot cycle of the Sun is also accompanied by a reversal of its magnetic field. Discussion of the reversal of the Earth's magnetic field in the geologic record and the current decrease of its magnetic field, what it might mean, whether the Earth's magnetic field is going away for good or merely about to reverse polarity after some 720,000 years since the last apparent reversal. Mars once had a magnetic field, now it doesn't. Solar wind may have blown away the atmosphere. Back to Chapter 6 and our Solar System. The "Thousand AU" mission -- a proposal to send a probe 1000 AU (about 100 billion miles) up out of the plane of the Solar System, so it can look back and take pictures of the entire Solar System at once. Without sensitive instruments, what you would see at that distance is the bright spot of the Sun -- that's all. Divide the planets into the rocky or terrestrial planets (Earth-like) and the gas giants (Jupiter, Saturn, Uranus, Neptune). Consider Jupiter to be a failed star -- too small for the hydrogen to compress and ignite in fusion. Many planets have moons -- they are all rocky. Many planets have rings -- Saturns are merely the most spectacular.
Wednesday 3/16: Exercise: What does random look like? Pick five random numbers from the whole numbers (integers) between 1 and 50. The sequence 5-15-25-35-45 is a list of five numbers in the range, but they are evenly spaced. Not common. Likewise 1-2-3-4-5, a straight run, is one of only 46 straight runs in all the possibilities. Often, though, a random sequence has two adjacent numbes: 3-9-22-23-42. This means that it is not unrealistic to imagine an interstellar cloud of gas and dust would have some lumpiness to it, as well as a slight sense of rotation. The formation of our Solar System. Second Generation star system -- otherwise there'd only be hydrogen. Death throes of some large stars throws off higher elements. Gravitational attraction of interstellar dust cloud. Any sense of rotation is exagerated by the Conservation of Angular Momentum -- the rotational speed goes up as the radius gets smaller. Do we have the only solar system with planets? No. Though to be fair, (1) we cannot see any planets around other stars directly, just as we cannot resolve any distant star into a disk in a telescope -- they are too far -- and (2) those planets we detect by indirect means must be very large, very strange planets. The rotating disk of gas and dust flattens as it speeds up. Irregularities and uneveness cause clumps to form -- these may become planets. Most of the planets in the Solar System have their orbits within a few degrees of the plane of the Earth's orbit around the Sun. Most, but not all, of the planets rotate in the same counterclockwise direction, as do the orbits of the moons of other planets. What about the space between the planets? While thinner, it is still full of gas and dust... until the Sun ignites and the solar wind clears out this gas and debris. Quiz 8, take-home, due Wednesday 23 March 2005.
Friday 3/18: The Solar Nebular Theory. A strong model of solar system formation must not only account for the basics of our solar system, but also provide some explanations for some of the anamolous parts, too, such as Earth having a large moon, Uranus' tilt, etc. The solar nebula cloud of gas and dust probably needs some shock to start collapsing, such as the expanding gas cloud from a nearby supernova (possibly from another of the 1st generation stars). Why do we have terrestrial (Earth-like, rocky) and jovian (gas giants, like Jupiter) planets? First of all, 98% of the material in the solar system is hydrogen and helium. Only 2% is everything else. You, for example, have more atoms of hydrogen than any other kind -- after all, you are mostly water and in every water molecule there are two hydrogens for every oxygen. It is usually said that there are 92 naturally occuring elements, which used to be considered hydrogen (H) through uranium (U) in the periodic table. However, element 94 plutonium is probably naturally occuring, while element 43 technitium essentially doesn't occur in nature, so we can still use the 92 element list. (Other elements above 92 in the periodic table have to be made in reactors or accelerator laboratories and mostly don't live very long.) Elements above number 26 iron have to be produced in the "death throes" of a supernova star. So as material concentrates during the collapse of the solar nebula, some will begin to condense around "seeds". Planetesimals form, which can collide and coalesce into the planets, or if they aren't big enough, collide and splash more debris into the mix. The jovian planets will form further out than the terrestrial planets, but their large gravity will leave some rocky material in orbit about themselves -- hence one of the reasons that Jupiter, etc., have numerous moons (other moons are captured asteroids and other bodies passing by). Earth's large moon was not formed by this process and Mars' two moons are small rocks, so their rocky planetesimals coalesced together, but didn't form moons.
Monday 3/21: The Solar Nebular theory model of solar system formation. So far it explains the main features of our Solar System: rotating system with (most) of the rotations in the same direction; jovian gas giants condensing out further from the center than the rocky terrestrial planets; no moons from initial formation on inner planets, many moons around jovians; central star with most of the mass. But the model also has to accommodate or explain the variations: (1) the unusual rotations of Venus and Uranus, (2) Earth's large moon, etc. Much can be explained by collisions. As the seeds bring rise to planetesimals and the planetesimals fracture and coalesce, the growing planets' gravity and previous collisions can put the remaining planetesimals on non-circular orbits. Eventually they can slam into the new planets. Really large events can knock a planet around. In Earth's case, we may have been hit near dead-on with one large object, which kicks out a large, but slower moving blob, which falls back to the Earth and in a secondary collision, what becomes the Moon is ejected. Since heavily made of crust material, the Moon is more metal poor than the Earth. Mercury looks like our Moon -- heavily cratered. But Earth isn't. Why? Because of active geology on Earth -- Plate Tectonics on Earth. Did not have an understanding of plates until early 1970s. (Much like we didn't know that the Milky Way was just one galaxy of billions of galaxies until the 1920s.) Even from the Earth, you can see large craters on the Moon. And also huge smoother regions -- mare or "oceans" -- where lava flow filled in part of the holed surface, and has much smaller, less numerous craters now. (The "big chunks" are much rarer now.)
Wednesday 3/23: The Age of the Solar System can be estimated by dating rocks. Radioactive materials like Uranium-238 are both common and long-lived. The half-life of a radioactive material is the time it takes for half of the original material to decay into something else. In the case of the oldest solar system rocks, about half of the Uranium-238 has decayed into Lead-206, and the half-life of Uranium-238 is 4.5 billion years. The oldest Earth rocks are about 4.3 billion years old, but that only puts a minimum on the Earth's age -- it took some time for the early Earth to cool sufficiently to form a crust and form rocks. We have good chemical evidences that some meteorites that land on Earth are from Mars. Most date to only 1.3 billion years ago, but one dates to 4.6 billion years ago. The Sun appears to be at an age in its life cycle of 5 billion years ± 1.5 billion years, which is in agreement with other data. The Inner/Rocky planets go through a similar set of four stages of planetary development: Differentiation (where different layers form inside the planet), Cratering (when large objects in the solar system are still around to bombard the surface), Flooding (when molten rock heated by radioactive decay wells up to the surface and spreads around) and Slow Surface Evolution (the last 3.5 billion years of Earth history, with plate tectonics, mountain formation, erosion, etc. in play to change the surface of the Earth's crust). Kepler (and others) wanted to make sense of the apparent spacing of the planets - it just looks like it might be meaningful. Bode's law (see Quiz 9, NOT your textbook) is an example of an "empirical law" -- one that mimics the data, but is not a scientific theory that offers an explanation as to "why". It predicts a planet where the asteroid belt exists -- perhaps a planet broke up there or couldn't form due to Jupiter's tidal forces. The orbit of Neptune, however, is not "on the list". Hand out Sample Exam 3. Quiz 9, Take Home -- due Wednesday 30 March 2005.
Friday 3/25: YES -- we have class today. But Exam 3 is moved to Wednesday 30 March 2005. "Flotsam and jetsam" -- the leftover bits from solar system formation. NOTE: Some of this material shows up in Chapter 9 in your textbook, so it appears here out of order, but it is relevant. Two main classes of things: (1) Asteroids (rocky) and (2) comets (icy). Most asteroids are located in the Asteroid Belt between Mars and Jupiter. Our Bode's Law exercise (Quiz 9), "suggests" that a planet could be located there. Perhaps it formed, but was ripped apart by proximity to Jupiter's strong gravity creating large tidal forces every time it passed. Perhaps Jupiter's gravity kept the planetesimals from coalescing into a single planetary object and remained thousands of asteroids. Perhaps the "missing" planet formed and was destroyed in a cataclysmic collision. Some asteroids are closely associated with Jupiter's orbit, some have been plucked out by Jupiter and other planets as moons, either long term or temporary. Some are Earth-crossing asteroids -- their elliptical orbits cross our own. However, some of these are at an angle which poses little threat and most are too small to worry about. A meteor is any object which falls into the Earth's atmosphere and glows. A meteorite is any meteor which survives to the ground and doesn't burn up completely. Your textbook refers to meteorites as falling into two categories: Primitive (likely to contain "primordial" material from the solar system formation) and Processed (material that has been through planetary formation, probably debris blown off from a collision). Meteor showers occur at predictable times in the calendar when the Earth passes through a trail of mainly microscopic debris, usually leftover from the passage of a comet. The Leonids, for example, show up in mid-November. During their peak, one might observe hundreds or even a thousand of bright streaks of light seeming to radiate out from a central point -- in this case the constellation Leo. Comets have been described as "dirty snowballs" and their nucleus consists of water ice and some rocky material. Comets typically travel in very eccentric orbits, spending nearly all their time at aphelion. As they swoop in towards the Sun, they heat up, expel water vapor and form a tail which always points away from the Sun -- that means comets "back" out from perihelion. Why do these smaller objects, comet nuclei and small asteroids and moons, tend to look like lumpy potatoes? Because they aren't big enough to circularize through their own gravity, and heating/collisions tends to make pieces come off irregularly.
Monday 3/28: Comments on Exam 3 material -- we've talked about the Sun (Ch. 10), light and the EM spectrum earlier (Ch. 5), lots on Solar System formation (Ch. 6), touched on planetary topics (parts of Ch. 7 & 8), and asteroids and meteors/meteorites (part of Ch. 9). Continue looking at Terrestrial planets. Comparison photos in Ch. 7 of Mercury, Venus, Earth, The Moon and Mars -- both same-scale whole planet and close-ups of surfaces. Mercury and our Moon look very similar. Active geology -- plate techtonics -- on Earth has wiped away most of the cratering. And the atmosphere and water has provided weathering and runoff which changes the surface. Evidence for water on Mars includes what looks like riverbeds (but not Percival Lowell's famed but misguided sightings of an elaborate series of Martian canals) and we started the course talking about the hematite "blueberries" which on Earth require water to leech the iron from the rock. BTW- To see "canals" on the surface of Mars from the Earth would make them far larger structures than we have ever built. With naked eye, and not binoculars or telescopes, cannot really see any manmade objects from Low Earth Orbit, though the city lights at night are pretty.
Wednesday 3/30: Exam 3 re-scheduled to here.
Friday 4/1: NOTE: When Dr. Phil got his sinus cold, he got behind in updating the lecture notes -- so the dates are approximate for the next week's worth of material. The sol (local year) for Mercury is 88 days. The Mercury "day" is about two-thirds of this, so it isn't quite rotation locked like our Moon going around the Earth, but it does mean that days and nights are really long -- huge difference in temperature between dayside and nightside. Comparison views in textbook of internal structures of the planets. Varying thickness of crusts and cores, which will change conditions on surface. Line of solidity is near crust on the Earth, so the crust "floats" and we get plate techtonics. Mercury is solid to near core, rigid structure, no plate techtonics. How do we know what the interior of planets looks like? For one thing, we have evidence of the interior to our own planet, from the seismological evidence. Demo: an extra-long Slinky can demostrate both kinds of vibrations. Side-to-side waves (transverse or s-waves) are like the vibrations of a string in a guitar or a piano. Compression waves (longitudinal or p-waves) are like sounds waves in air. When an earthquake or other large event happens on the Earth, s- and p-waves radiate away from the site. They get bent or reflected off the various interior layers -- except that s-waves can't go through the liquid outer core. Detecting stations around the world monitoring the same event get different readings at different times, which we can use to reconstruct the interior of the Earth. Likewise, the Apollo astronauts left seismological gear on the Moon -- and from small impacts, explosive charges and dropping rockets onto the Moon, we know similar information about the Moon.
Monday 4/4: Volcanoes. On Earth, with plate techtonics, the crustal plates may be moving relative to a "hot spot" deeper in the Earth, so that one gets a volcanic "chain", e.g. the Hawaiian islands. On Mars, the crust does not seem to be moving, at least not today, so Olympus Mons, the largest volcano in the Solar System, just keeps on getting bigger. Mars as "the freeze-dried planet". Discussion of freeze drying process, as well as the nature of dry ice -- actually solid carbon dioxide. On the Earth (and on Mars), the air pressure is too low for liquid carbon dioxide to exist, so dry ice doesn't melt, it sublimates -- goes directly into a gas.
Wednesday 4/6: Potential for terraforming Mars? (i.e. making it Earthlike) There is water ice and dry ice in the polar caps. Put something black on the caps and they will heat up during the summer. Black dust? Dark bacteria? (We've found bacteria which can live in extreme environments on Earth, including in Antarctica. Venus similar to Earth in some ways, very different in others. Surface not known before radar mapping, and a Soviet lander, hidden beneath thick cloud layers. High temperatures and pressures in an atmosphere of carbon dioxide and sulfuric acid -- a greenhouse effect run wild. Venus may have had plate techtonic activity, evidence of large-scale surface restructuring, which ended xxx hundred million years -- estimated by looking at cratering density, compared to other terrestrial planets.
Friday 4/8: Return X3 and hand out solution. Gas Giant planets. We believe that all four Jovian planets each started from about the same sized planetesimals -- some 10 times the mass of the Earth. Since they started out with much more mass than the planetesimals which formed the terrestrial planets, they could pull in condensing hydrogen and helium and keep it. Jupiter ended up with over 300 Earth masses of H and He, Saturn pulled in 75 Earth masses of H and He -- it isn't that much smaller than Jupiter, because it simply isn't as dense. Neptune and Uranus are smaller and quite a bit different. Uranus, for example, started with a planetesimal of 10 Earth masses and is currently 14 Earth masses -- so it's rocky core is an appreciable size proportionately. Jupiter is the largest, with 71% of solar system's planetary mass. Mainly hydrogen, followed by helium, plus water vapor, methane, ammonia. Large mass means large gravity means large pressure. Liquid metallic hydrogen starts not so far down. (Without such extreme pressures, we don't think about hydrogen as having a metallic state.) Allows for huge electrical currents and gigantic magnetic field. Magnetosphere of Jupiter is huge, much larger than Earth. Auroras in Jovian atmosphere, like Earth, but bigger. Rocky core, where rocky refers to composition, not necessarily solid rocks. Some years ago, scientists speculated that since Jupiter contains organic chemicals (means containing carbon), the extreme pressure deep inside Jupiter might pull carbon out of molecules and compress into high pressure form of solid carbon -- i.e. a giant diamond. Speculation is one of the things that scientists do -- always throwing new ideas out into the field to see where it might lead. Other scientists pick these speculations apart, suggest experiments to confirm or disprove. Science advances. Belt Circulation Patterns: The Jovian atmosphere rotates at different speeds in great circulation belts at different lattitudes. The Great Red Spot is a huge storm on the face of Jupiter that has persisted, changing in size and color over the centuries. The different colors are different chemicals condensing out at different temperatures at different layers -- much like we have white clouds of water vapor on the Earth. The whistling steam kettle: the white cloud forming outside the teakettle is not steam, but condensed water vapor - it is cool and damp if you wave your hand through it. There is, however, a clear gap between the whistle and the white cloud -- like the gasses in the air we breathe, steam is clear. Do NOT put your hand in that gap, it will get severely burned by steam at a temperature above 212°F or 100°C. Hand out first Sample Final Exam -- see class homepage for some of the answers.
Monday 4/11: All those moons... First four planets only have three moons -- and the two around Mars are pretty wimpy. The Jovian planets have lots of moons. When Galileo first used his new telescope to look at the heavens, he saw a small disk for Jupiter and four nearby dots. Over successive viewings the four dots moved back and forth around Jupiter -- and Galileo realized he was looking at a small "planetary" system of moons orbiting Jupiter, he had just been seeing them edge-on. The 4 Galilean Moons: Ganymede, Europa, Callisto, Io. Io has terrible weather -- active volcanoes spew sulfurous compounds. Indeed, Io is the most volanically active body in the Solar System. But why is Io geologically active? It is about the same size as our Moon, so it's internal heat should have been shed by now. The answer is tidal heating. Io is close to Jupiter, whose gravity is enormous. So just like a variation in the gravitational attraction to the Moon between the ocean nearest the Moon, the center of the Earth and the ocean the furthest from the Moon creates two High and two Low Tides, the tidal forces on Io as it rotates causes the interior to flex and heat up from friction. In addition, Io's orbit is more eccentric than the other Galilean Moons because of the timing of the orbits. For every orbit by Ganymede, Europa does two and Io does four. When the other moons line up with Io, they pull it away from a perfectly circular orbit. Europa has a cracked, icy surface, but may have liquid water under the ice. The water layer may be up to 100 km (61 miles) deep. Though Europa is smaller in diameter, Earth's seas are relatively shallow (RMS Titanic in the North Atlantic is only 2.5 miles down, and the Marianas Trench, the deepest spot in the ocean, is only about 7 miles deep) in comparison, so there is much more water on Europa than on Earth. Ganymede and Callisto also appear to have water, and there is evidence of water-ice volcanoes which have smoothed out vast crater fields. One more thing about Jupiter. In the Earth-Moon system there are 5 Lagrange Points, L1 through L5, where an object in orbit stays in the same place relative to the Earth-Moon line. L1, L2 and L3 are unstable, drift away from the point and you don't come back. But L4 and L5 are stable -- indeed, radar confirms there is a collection of debris there. The L5 Society wants to build a huge space station at L5, where it will naturally stay put due to gravity. Well, there are two Trojan Points in the Jupiter-Sun system like L4 and L5. And there are two sets of Trojan Asteroids which have collected there, in Jupiter's orbit, but some large distance away
Wednesday 4/13: More moons. Saturn has one large moon, Titan, which we talked about early in the semester. Textbook refers to it as having a "smoggy" atmosphere. Many interesting things happen if a moon/planet has an atmosphere, but frustrating to astronomers when it is opaque and we can't see the surface (Titan and Venus). Earth's clouds are also opaque, but they don't cover the entire surface at once. Mars can have huge sandstorms, but they subside. Saturn also has six medium-sized moons. Why should the icy moons of the gas giants have such active geology? Because they are icy moons and not rocky. The large gravity of the gas giants means there can be tidal heating, and frankly, ice melts at a lower temperature than rock does, so can have icy, slushy, watery interiors, which can leak, well out or erupt from icy volcanos. We see evidence of cracks and fractures on icy surfaces, plus vast areas smoothed out and much less cratering left versus rocky moons. Oddballs: Neptune's moon Triton is an oddity, in that it is a large moon, yet it orbits Neptune in the "wrong" direction and at a steep angle to the equator for such a large moon. Bizarre surface -- part of it is described as like the skin of a cantaloupe. When we talked about Solar System formation models, we indicated that the model had to be robust enough to allow for Uranus' axis of rotation to be tilted on its side, versus other planets. The suspicion is that Triton was captured by Neptune in some large event, and that Triton probably orbited the Sun originally as a large asteroid or a small planet in its own right. All the gas giants have ring structures, but of course we immediately think of Saturn when we talk about rings, because Saturn has the most complete and spectacular set. The other gas giants' rings tend to be thinner and sometimes incomplete. Even from Earth-based observatories, it is possible to see some structure in Saturn's rings -- changes in brightness and gaps. In some of the gaps, there may be a small moon which has cleared the path. Or a very thin band may have two "shepherd moons" on either side of it, whose orbital dance confines the material to a thin line. The rings themselves are made of ice crystals, dust, "small" rocks. One of interplanetary probes dove through Saturn's rings and survived. Does Earth have a ring? Well, maybe. There are certainly bits of debris in orbit about the Earth, and we mentioned using radar to confirm that there is debris collected in the two Lagrangian points L4 and L5. And we are slowly establishing a tiny artificial ring of geosynchronous satellites which must orbit above the equator at a fixed distance of some 25,000 miles in order to appear to remain fixed in the sky, so all of our satellite data and TV dishes point to our south here in Kalamazoo. Some call this the Clarke Belt, named after Arthur C. Clarke who first proposed the concept of geosynchronous satellites. Finish up the day with the course & teacher evaluations for the semester. Q10 Take-Home, due Friday 15 April 2005, but will accept until 5pm on Monday 18 April 2005. Hand out second Sample Final Exam.
Friday 4/15: LAST DAY OF CLASS - AND ALSO DAY THAT FEDERAL AND STATE INCOME TAXES ARE DUE. -- Course Review.