## Lectures in PHYS-104 (1)

Updated: 09 December 2003.

### Week of December 8, 2003.

THURSDAY 12/11: FINAL EXAM - 10:15am to 12:15pm - 1104 Rood Hall

### Week of August 29, 2003.

Friday 8/29: Class begins. Distribute syllabus. Introduction to Dr. Phil (videotape presentation). Scare students to death. The Solar System is our local neighborhood. Mars in the current night sky -- closer to Earth at end of August than in a long time.

### Week of September 1, 2003.

Monday 9/1: LABOR DAY HOLIDAY - No Class.

Wednesday 9/3: What color is the sky? Daytime: why is the sky blue? Nighttime: why is the sky black? What does one see? Daytime: Sun, Moon, occassionally other things. Nighttime: Moon, Planets, Stars, Comets, Meteors/Meteorites. What shape is the sky? Bowl shape is something of an optical illusion. Looking up in the sky in ancient times, before city lights made it hard to see the stars and electric lights kept us inside.

Friday 9/5: Discussion of size. Miles. Kilometers (km). The Astronomical Unit: 1 AU = 93 million miles = orbital radius of Earth's orbit. The Light Year: How far light travels in a year. 1 LY = 186,000 miles/sec x 3600 sec/hour x 24 hours/day x 365 days = 5,865,696,000,000 miles or almost six trillion miles. The nearest star is over 4 L.Y. away. 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. 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.

### Week of September 8, 2003.

Monday 9/8: Chapter 1 images -- Size and Scale of the Solar System, starting with 52 foot by 52 foot square and increasing each dimension by a factor of 100 between images. Get up to 10,000 miles x 10,000 miles and show Earth as the big blue marble.

Wednesday 9/10: Chapter 1 images (con't.) -- From the Earth up to 1 trillion miles (1,000,000,000,000 miles). Note that a light year is nearly six times this. Relative size between Earth and Moon. Relative size between Earth and Sun. Orbits of the Inner Planets (Mercury, Venus, Earth, Mars) and Outer Planets (Jupiter, Saturn, Uranus, Neptune and Pluto). Pluto is the "odd" planet. Topic 1 assigned (see Movielist).

Friday 9/12: Chapter 1 images (con't.) -- From 1 trillion miles out to the nearest stars, the Orion Arm of the Milky Way galaxy, the Local Group of galaxies. Quiz 2 take-home obstensibly due Monday 15 September 2003, but date may be extended if people have questions.

### Week of September 15, 2003.

Monday 9/15: We classify or categorize objects in the sky by Size, Brightness, Color, Place, Association, Orientation, etc. Need to differentiate between "Apparant" values of these classifications and their "True" values. "Apparant", because our observations are based on what we can see from the Earth. Stars linked in our view of the sky, may not be close to each other in real life. As you move away from Earth, the arrangement and order of the stars will change, as well as their visibility, so if you were on another planet around another star, you would not necessarily see the same constellations as we do today. Also, our view of the stars is a snapshot in time. As the stars move, their place in our sky changes. Not everyone sees the same thing. "Normal human vision" can see 6 stars in the Pleiades (The Seven Sisters), but someone with 20:15 vision might see seven. 88 Constellations by international agreement. Some groupings of stars that we take as constellations are in fact considered to be an asterism and are subsets of one of the listed constellations. The Big Dipper is part of Ursa Major (the Big Bear). Of the thousands of stars that can be seen in the night sky, a few have unique names that are remembered today. Most star names are assigned to a constellation with a Greek letter in descending order of brightness (alpha Canis Major), or from some astronomer's star catalog. Quiz 2 take-home now due Wednesday 17 September 2003.

Wednesday 9/17: Some useful geometry info: Circles (C = 2(pi)r ; A = (pi) r²), Spheres (A = 4(pi) R² ; V = (4/3)(pi) R³). The brightness of an object falls off as 1/r², the total light from an object divided by the surface area of a spherical "bag" put around the object. Apparent Magnitude, Absolute Magnitude. Old form: visible stars ranked first class through sixth class stars. New form: visible stars are magnitude 6 and brighter. Quiz 3 in-class. Quiz 2 due today.

Friday 9/19: Extend apparant magnitude scale to include objects fainter than can be seen by naked eye, and brighter up to the Sun as seen from the Earth. Compare brightness of objects with differing magnitudes. Every 5 magnitudes difference is a factor of 100 in the Intensity (brightness). Every magnitude difference is a factor of about 2.5 in Intensity. The magnitude system is a log scale -- allows things of wildly different levels to be plotted easily. More next week. Start talking about coming up with a coordinate system for the sky. Earth tilted on axis (turns out to be 23½°).

### Week of September 22, 2003.

Monday 9/22: Fall Equinox scheduled for Tuesday 9/23 in the early morning. 12 hours 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. The sun, moon, planets, comets, asteroids, etc. are not "fixed" on the Celestial Sphere. Celestial North/South Poles. Star trails -- long exposures of film -- show the motion as the stars "wheel" around the heavens.

Wednesday 9/24: Using equations for finding Apparent Visual Magnitude and Intensity (Brightness) Ratio. Example: The Sun is magnitude -26.8 as seen from the Earth. What is its apparent visual magnitude as seen from Neptune? Further discussions of coordinates on the Celestial Sphere. "Distances" between objects given by angular separation. Using hours and degrees. Q4 Take-Home will be handed out on Friday, though Dr. Phil set up the problem in class.

Friday 9/26: If we give the equitorial position on the Celestial Sphere in hours, then 360° ÷24 hours = 15° per hour. 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. The Moon, when visible, provides light for work and travel. Tides: High and Low (oceans more or less attracted by Moon's Gravity). IMPORTANT NOTE: Exam 1 has been moved from Wednesday 1 October 2003 to Wednesday 8 October 2003.

### Week of September 29, 2003.

Monday 9/29: 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. Phases of the Moon as seen from the Earth. Q4 Take-Home now due Wednesday 10/1.

Wednesday 10/1: "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. 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.) Next, we defined the lunar year which we call a month ("moonth"?). But we have to be careful with definitions. There's the sidereal period -- 27 days, 7 hours, 43 minutes, and 11.5 seconds -- the time for the Moon to make one orbit about the Earth by returning to the same point in the sky. Another period of some 28 days, brings the Moon back to the orbital path of the Earth (which is curved around the Sun). And finally, the synoptic period -- 29 days, 12 hours, 44 minutes, and 2.8 seconds -- which brings the Moon back around in relationship to the Sun (which moves through the celestial sphere as the Earth goes around the Sun), and gives one full cycle of phases of the Moon. 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. Q5 Take-Home due Monday 10/6.

Friday 10/3: Eclipses can only occur when the New or Full Moon is in the plane of Earth's orbit around the Sun -- otherwise the relevent shadows miss their targets. This happens about every six months. Angles: we can divide the full circle into 360°, we can divide each 1° = 60 arcminutes = 60', and each 1' = 60 arcseconds = 60". So 1° = 3600". Small Angle Approximation -- confirm that the apparent angular diameter of the Moon and the Sun as seen from the Earth are about the same. Solar Eclipses occur at New Moons. Lunar Eclipses occur at Full Moons, when the Moon slips into the Earth's shadow. Actually the shadow is divided into two parts -- the total shadow (umbra) and the partial shadow (penumbra). The umbra only extends so far from the Earth -- when the apparent visual size of the Earth is less than the apparent visual size of the Sun, you cannot have a total shadow. As the Moon moves into the penumbra, the Full Moon begins to dim from one side to the other. As the Moon moves into the umbra, there is a small amount of red light "leaking" around the Earth (what's left after the blue light is scattered in the daytime sky) and so the Moon turns blood red at totality. Like Solar Eclipses, we can have partial or total lunar eclipses. Since the Earth's shadow is larger, half a lunar month before or after a Solar Eclipse, the Full Moon is still likely to be close enough to the plane of the Earth's orbit to get a Lunar Eclipse -- so in general there at least twice as many Lunar as Solar Eclipses.

### Week of October 6, 2003.

Monday 10/6: Comments on Elliptical Orbits. 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. Exam 1 Review.

Wednesday 10/8: Exam 1.

Friday 10/10: 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. Early Astronomers. The Greek Philosophers may not have been the first scientists, but we know much of what they wrote. They believed in perfect cycles and perfect geometries, even when their models didn't support their observations.

### Week of October 13, 2003.

Monday 10/13: 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. Plato / Aristotle, Ptolemy, Copernicus and Kepler.

Wednesday 10/15: 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. NOTE: Exam 2 is scheduled for Wednesday 22 October 2003. It is correct in the syllabus except on the last page.

Friday 10/17: Return Exam 1 and go over answers. 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, combined with Universal Gravity to try to find the period T, to make one orbit, in Quiz 6 Take-Home, due Wednesday 22 October 2003.

### Week of October 20, 2003.

Monday 10/20: Kepler's Three Laws of Orbits: (1) All planetary orbits are ellipses with the Sun at one focus. (2) Equal Area Rule -- The time is 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. (3) The Period Rule. For the orbits about any given body, the square of the period (T) is proportional to the cube of the radius (semi-major axis, r). 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.). Galileo comes in between Kepler and Newton. Galileo's observations and his trial.

Wednesday 10/22: Exam 2.

Friday 10/24: Return Exam 2 and go over answers. 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)

### Week of October 27, 2003.

Monday 10/27: 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 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. On the other hand, 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 by 2006, 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.

Wednesday 10/29: Telescopes -- Optical: Refractors (lenses) and Reflectors (mirrors and mixed mirror-lens systems). Radio telescopes. UV, X-ray, Gamma-ray telescopes. Q7 Take Home, due Monday 3 November 2003.

Friday 10/31: Our Sun. A completely average and boring, ordinary star -- and a good thing, too. 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. 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. The radiation can't get straight out -- it gets absorbed, reflected, re-radiated at lower frequencies. Eventually, after over seven million years, the light finally reaches the surface, where it takes just eight minutes to cross space to the Earth.

### Week of November 3, 2003.

Monday 11/03: 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. NOTE: Unless you handed in a DRAFT paper, your Topic 1 movie report is due today, Monday 3 November 2003 by 5pm. If you handed in a DRAFT paper, please remember to turn in both your marked-up DRAFT paper and FINAL paper.

Wednesday 11/05: The structure of the sun: central core, photosphere (bright), thin chromosphere above (dimmer), high temperature thin corona away from surface. Solar winds carry small fraction of mass away at speeds up to 1000 km/hour, but still 10,000,000 tons/year. Sunspots are magnetic effects -- they come in pairs. The leading spot is a North magnetic pole and the trailing is a South. The 11-year sunspot cycle. 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. 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. Granularity of the solar surface. Dr. Phil's "Oatmeal model". Q8 Take-home, due Monday 10 November 2003.

Friday 11/07: The "heliopause", where the Sun's solar winds meets the interstellar wind. The edge of the Solar System. Of the four deep space solar system probes launched in the 1970s (Pioneer 10 and 11, Voyager 1 and 2), Pioneer 10 was launched first, but Voyager 1 is the furthest out -- about 8.5 billion miles, maybe 90 A.U. They have recorded one event, possibly a shockwave near the heliopause, but not the actual edge itself. Next, remember those solar flares last weekend? Well, despite our being in a solar minimum period, the solar flare that occured on Tuesday was one of the largest recorded -- fortunately the sunspot was just going around the edge of the sun and so we did not get hit with the full effect of the blast. You can read a more full report at space.com -- and also about the Solar Flare of 1859, which causes fires up and down the United States and England along their telegraph lines. Oh, and we moved Exam 3 a week later from November 12th to November 19th.

Saturday 11/08: As the Moon was rising in the East, up by us there were clouds coming in from the West. Would tonight's Lunar Eclipse get cut out, too? No -- we went out at around 9pm and saw a Moon mostly dark, with a bright crescent running along the bottom left edge. Very cool.

### Week of November 10, 2003.

Monday 11/10: 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.

Wednesday 11/12: 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. 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". NOTE: Exam 3 has been moved one week to 11/19 Wed. Q9 Take-Home, Due Monday 17 November 2003.

Friday 11/14: 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).

### Week of November 17, 2003.

Monday 11/17: Run through Sample Exam 3. Continue looking at Earth-like terrestrial planets. The four stages of planetary development. Plate Tectonics on Earth -- active geological surface. 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.)

Wednesday 11/19: Exam 3.

Friday 11/21: Albedo is a measurement of the reflectance -- how much light that 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. 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? Discussion of PBS Nova episode on the decrease of Earth's 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. Mercury's core is almost as large as the Earth's, but very little mantle and crust. Mercury closest to Sun. Describe computer study during Dr. Phil's college days trying to determine if Earth is maintaing, gaining or losing temperature over the long term.

### Week of November 24, 2003.

Monday 11/24: Return X3. I have added Exam Solutions for X1, X2 and X3 to the class webpage -- these are in Adobe Acrobat .PDF format, so you have to have the Acrobat Reader (free), but you will be able to view, magnify and print out the solutions if you so choose. Blue Sheets, too. 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. The Outer Planets: Jupiter (Great Red Spot, largest of our planets), Saturn (with its very visible rings), Uranus and Neptune (once thought to be "twins"), and Pluto (really the Pluto-Charon System, where Charon isn't all that much smaller than Pluto). When Dr. Phil taught an Astronomy course at GVSU in the Summer of 1994, I explained to those students that we had an exact date when their textbook would become obsolete -- the day that the pieces of comet Shoemaker-Levy 9 struck Jupiter. This comet got too near Jupiter, broke into many pieces by tidal forces, then traveling like a train or a string of pearls, Shoemaker-Levy 9 came round again and impacted on Jupiter. First large scale collision witness in modern detection era.

Wednesday 11/26: WMU Classes end at NOON -- Dr. Phil's other two classes are cancelled to keep them in synch -- So no PHYS-104 today either.

Friday 11/28: Thanksgiving Break. No class.

### Week of December 1, 2003.

Monday 12/1: Classes Resume. Gas Giant planets. 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. 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. 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. Gravity rules the giants. Tidal forces from Jupiter might have either broken up a planet between Mars and Jupiter or prevented it from forming -- either way, we have an asteroid belt. Newton's Universal Gravity equation has two masses -- it is a two-body problem and can be solved exactly, if there are no other masses. But in general there are other masses, and the n-body problem (n > 2) cannot be solved in closed form, except for very special cases. Lagrangian points about Earth-Moon system -- L1, L2, and L3 are unstable, L4 and L5 are stable -- radar indicates that junk has collected there. L5 has been proposed as a place to put a big space station. Similarly, Jupiter attracts debris, rubble, asteroids, and some of this junk orbits the Sun ahead or behind of Jupiter at the Trojan points, something like L4 and L5. Why does Saturn have such sharply defined rings that seem stable for so long? Shepherd moons -- two small moons which stabilize a thin ring. Or a moon which clears out a path in its orbit, leaving a division.

Wednesday 12/3: The Moons of Jupiter. The four Galilean moons (Callisto, Io, Ganymeade and Europa) are all around the size of Earth's Moon. Check text for brief descriptions. Life may be possible on one or more of these moons. Many smallers moons, the number changes as (a) we detect more of these small moons and (b) some of them are captured and some are released from Jupiter orbit over time. The Moons of Saturn. Titan is around Mercury's size. Why don't the rings condense into moons? Because they are located inside the Roche Limit. (For materials and planets of around the same density, the Roche Limit is 2.44 times the radius of the planet.) Inside the Roche Limit, tidal forces either pull a moon apart or prevent one from forming by gravity. So why do the shepherd moons and clearing moons persist? Who says they won't be torn apart by the tides? Why doesn't the Space Shuttle and the International Space Space inside Earth's Roche Limit get pulled apart? Because they aren't held together by their gravity, but by bolts and welds. See sidebar story on How does Science get funded?

Friday 12/5: REVIEW. Q10 points awarded as in-class attendance