Cahaba School                                                                                                                                                                                                                                                                                                  Astronomy Picture of the Day                                                                                                                              | Today's Picture | Archive | Search | Calendar | Cosmos Stars : Binary Stars * Black Holes * Globular Clusters * Individual Stars * Neutron Stars * Nurseries * Open Clusters * Sun * White Dwarfs Galaxies : Clusters of Galaxies * Colliding Galaxies * Elliptical Galaxies * Local Group * Milky Way * Spiral Galaxies Nebulae : Dark Nebulae * Emission Nebulae * Planetary Nebulae * Reflection Nebulae * Supernova Remnants Miscellaneous : Quasars/Active Galactic Nuclei * Dark Matter Solar System Sun * Mercury * Venus * Earth * Earth's Moon * Mars * Jupiter * Jupiter's Moons * Saturn * Saturn's Moons * Uranus * Neptune * Pluto Comets --- Hyakutake * Hale-Bopp * Halley Asteroids Space Technology Rockets/Launch Vehicles * Orbiting Observatories * Space Stations * Earth Observatories Sky Messier Objects * Sky Views People Scientists * Astronauts Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA) NASA Technical Rep.: Jay Norris. Specific rights apply. A service of: LHEA at NASA/ GSFC &: Michigan Tech. U.   Cahaba School Astronomy   You are responsible for all links & homework assignments   Take notes on each chapter   Lab    Portfolio of articles on astronomy (1 each month)     August:  Ch. 1 & 2 September:  Ch. 3 (Project 1 and Planetarium) Project 1:  Constellations What is a constellation? What is the real purpose? Pick a constellation and construct a model.  -Include both names (name and what it represents) -mythical background -which month is it best seen in the sky?  Suggestion: (black board with tack holes to represent stars, include names on front, on back you will include other information) October:  Ch. 4,  5, 6 November:  Ch. 7 December:  Ch. 8  & Project 2 1st Semester Exam Project 2:  Scientific Contributors Choose 1of the following & write a 2 page paper/MLA, Works Cited ·        Pythagoras of Samos (circa 580 - 500 BC) ·        Plato (circa 428 - 348 BC) ·        Eudoxus (circa 408 - 356 BC) ·        Aristotle (384 - 322 BC) ·        Heraclides (circa 388 - 310 BC) ·        Aristarchus of Samos (circa 310 - 230 BC) ·        Eratosthenes of Cyrene (276 - 194 BC) ·        Hipparchus of Rhodes (190 - 120 BC) ·        Ptolemy (circa 140 AD) ·        Nicholas Copernicus (1473 - 1543) ·        Johannes Kepler (1571 - 1630) and Tycho Brahae (1546 - 1601)                  Galileo Galilei (1564 – 1642)                  Isaac Newton (1642-1727) January:  Ch. 9 and Ch. 10 February:  Ch. 11 (Book- A Brief History in Time by Stephen Hawkings) March:  Ch. 12  & Project 3 Project 3:  Planets   (Make a model and include the Sun, all eight planets and their positions from the sun.  Be creative). April:  Ch. 13 May:  Final Exam (Write a paper about Astronomy Today and hopes in the future)   I.                  Chapter 1: Introduction A.     What is astronomy B.     The Scientific Method C.     Astronomy Vs. Astrology II.               Chapter 2:  Our Place in the Universe A.     Solar System Sizes B.     Cosmic Calendar C.     The motions of Earth III.           Chapter 3:  The Sky A.     The Sky B.     Constellations C.     Seasons IV.           Chapter 4:  The Moon A.     Phases of the Moon B.     Eclipses                                     i.      Solar                                    ii.      Lunar V.              Chapter 5:  A.     Shape and Size of Earth B.     Motion of the Planets VI.           Chapter 6:  Astronomy A.     History of Astronomy B.     Ancient Astronomy C.     Greek Contribution to Astronomy D.     Ptolemy E.      Astrology VII.       Chapter 7: A.     Islamic Contribution to Astronomy B.     Nicholas Copernicus C.     Johannes Kepler and Tycho Brahae D.     Galileo Galilei VIII.    Chapter 8: A.     Isaac Newton B.     Newton’s Laws of Motion C.     Circular Motion D.     Law of Gravity                                  i.      Kepler’s 3rd Law                                  ii.      Surface Gravity E.      Planetary Orbits F.      Tides IX.              Chapter 9:  Light A.     Light B.     Electromagnetic Spectrum C.     Doppler Effect D.     What can you learn from light? X.              Chapter 10:  Telescopes A.     Telescopes                                    i.      Purpose                                     ii.      Space telescopes                                      iii.      Detectors XI.              Chapter 11:  Solar System A.     Solar System B.     Planetary Facts C.     Mercury D.     Venus E.      Mars F.      Summary of the Jovian Worlds XII.       Chapter 12:  The Solar System A.     Jupiter B.     Saturn C.     Uranus D.     Neptune E.      Pluto and Charon F.      Asteroids G.     Comets H.     Summary XIII.    Chapter 13: A.     Meteors and Impacts B.     Formation of the Solar System C.     Other Planetary Systems Chapter 1 What is Astronomy? -- A Science. The study of the Cosmos - The Cosmos is all that ever was and all that will ever be - Cosmos is a Greek word meaning the Order of the Universe, it's the opposite of Chaos. The first science - Ancient people noticed that there were cycles in the sky and that the seasons changed with those cycles. Understanding the cycles meant being able to predict the seasons. - Cave drawings indicate that even Crow Magnon Man was aware of the celestial cycles. Astronomy vs. Astrology - Astronomy literally means the knowing (or naming) of the stars - Astrology literally means the study of the stars - But Astronomy has become associated with the scientific study of the stars and Astrology is associated with the mystical pseudoscience that believes that the heavens can directly influence our individual lives. What is Science? -- A Process of Inquiry. The Scientific Method Starts with a Question - the question may be brought on by an observation of a phenomenon - or it may be a "I wonder what if" type question Hypothesis - Once the question has been well formulated as many possible explanations or answers to that question should be formulated. Some times we call these models. - The major constraint on a hypothesis is that it must be testable. You must be able to do an experiment that could, at least in principle, disprove the hypothesis. - Religion and Pseudoscience are not scientific because their hypotheses are not testable. They cannot be disproved. - One should spin as many hypotheses as possible. Experimentation/ Observation - you must now conduct experiments or observations that will weed out your incorrect hypotheses. - this is perhaps the most important part of the scientific process. Report your findings - people make mistakes and the best way to guard against errors made in experiments is to report your findings to fellow scientists and allow them to review your work and repeat your experiments. - The phenomenon you are studying must repeat if it is to be testable in this way. If it does not, science cannot go further with it. - the process of peer review is one of the many error-correcting mechanisms built into the scientific method Draw Conclusions - Once everyone agrees on the experimental facts and observations, the remaining hypothesis that explains your phenomenon is accepted as a working theory. - If there are competing hypotheses that explain the data equally well, we choose the simpler one as the correct one. This is called the Principle of Occams' Razor - Generally a theory will generate new questions and the process repeats ad infinitum. - At many steps along the way new questions or new hypotheses might arise and the process repeats itself also. - If at any time in the future a new fact is discovered that contradicts a theory, the theory is first modified to include the new data. If it cannot be modified or becomes too complicated with the revisions, it must be thrown out. - Science is conservative in the acceptance of such new facts: "Extraordinary Claims Require Extraordinary Evidence" - Carl Sagan. Chapter 2 Our Place in the Universe Light has a a finite speed. Thus the information it brings is time delayed from its origin to us. The speed of light is 186,000 miles/second. The distance between Earth and Sun is 93,000,000 miles. Therefore it takes light about 8 minutes to travel from Sun to Earth. Thus we see the Sun as it was 8 minutes ago. It takes light 4 years to travel the distance to the nearest star system, Alpha Centauri. Thus we see Alpha Centauri as it was 4 years ago. We can define a convenient unit of cosmic distance: Light-Year - The distance that light travels in one-year. Alpha Centauri is 4 Light-Years distant. The Milky Way Galaxy is 100,000 Light Years across. The nearest big Galaxy is the Andromeda Galaxy at a distance of 2,500,000 Light-years. The most distant galaxies are 10,000,000,000 Light-years away or more. So we can See what the Universe was like 10,000,000,000 years ago, when the Universe was newly born. Scale of Space and Time Cosmic Calendar: Scale 12 Billion year History of Universe into one year. --> 1 month = 1 Billion years. Jan 1: The Big Bang Feb. : The Milky Way forms August 13: The Earth Forms December 13: Invertebrate Life Evolves December 25: Rise of Dinosaurs December 30: Dinosaurs Extinct December 31: 9:00 pm Earliest Human Ancestors December 31: 11:58 pm Modern Humans evlove December 31: 11:59:30 pm Agriculture Decmeber 31: 11:59:47 pm Pyramids are Built December 31: 11:59:59 pm Kepler and Galileo prove that Earth orbits the Sun.     Assignment: Chapter 1 & 2 Notes on chapter 1 & 2 (minimum 1 page) What is Cosmos? What is Occams' Razor? What is the speed of light? What is a light year? What is astronomy? What is the difference between astronomy and astrology? What are the steps to the scientific method and briefly explain each. Who is Carl Sagan? What is the nearest star system? How long does it take to travel to the nearest star system? Which planet has the largest diameter? Which planet is the third from the sun?     Chapter 3 The Sky What's in the Sky? (Click on links) Sun Moon Stars Planets     Milky Way Shooting Stars (Meteors) Meteor Showers  Comets  VERY IMPORTANT LINK: NASA http://science.nasa.gov   The Milky Way  A diffuse band of light stretching across the entire sky. Greek mythology held that it was the breast milk of Hera squirted across the sky. They called it Galaxy (which is Greek for "Milky Way"). African cultures referred to it as the backbone of night Galileo first observed that the Milky Way is in fact a vast cloud of countless stars. The Galaxy is a disk of stars in which we are embedded. This is why it looks like a band through our sky. Constellations (click on link for alphabetical listing of constellations and link to a minimum of 5) A constellation is an apparent grouping of bright stars in the night sky. The groupings are highly dependent on who is observing them. Currently, the International Astronomical Union (IAU) divides the sky into 88 regions it recognizes as Constellations. Stars in a Constellation are all in the same direction of the sky, but may not be physically close to one another in space. Stars so far away that there is no sense of depth in the sky. Everything appears as if it were on a sphere surrounding Earth. We call this imaginary sphere the Celestial Sphere. Seasonal Motions: As the Earth revolves about the Sun the Constellations visible at night change. Due to the tilt of Earth's rotation axis relative to it's orbital plane the Sun appears to change its location on the horizon where it rises and sets throughout the year. Cause of the Seasons (click on link)          Earth's Seasons Are Caused by the Axial Tilt! No Tilt, No Seasons. Solstices: Locations in Earth's orbit when the axis is pointed the most toward or away from the Sun. The longest and shortest day of the year depending on which hemisphere you live, North or South. Equinoxes: Locations in Earth's orbit when the axis is not pointed at all toward or away from the Sun, but tangent to it. Length of the day is the same for everyone on Earth. 12 hours of day and 12 hours of night. Seasons happen because sunlight is distributed over the surface of Earth differently throughout the year, NOT because the Earth is closer or farther away. When Sunlight is direct is delivers more energy per unit surface area than when it is indirect (or oblique). Tilt also causes length of days to change. During summer, days are longer and sunlight is more direct. During winter, days are short and sunlight is more oblique.     Assignment:   Notes on chapter What is the Milky Way? What is a constellation? Name and describe 5 constellations Are all constellations visible at night? Why/why not? What causes the seasons? What are solstices? What are equinoxes? What is the Celestial Sphere? What are days like during the summer and during the winter? Project #1:  Constellations  (Include the following information in your class presentation) Pick a constellation and construct a model.  -Include both names (name and what it represents) -mythical background -which month is it best seen in the sky?  Suggestion: (black board with tack holes to represent stars, include names on front, on back you will include other information) Chapter 4: The Moon  (click) Phases of the Moon  http://tycho.usno.navy.mil/vphase.html (click on to get today’s virtual reality phase of the moon)  Over the course of about a month the Moon is observed to cycle through a sequence of phases. As it changes its phase it also changes its position in the sky relative to the Sun. Hence, it rises and sets at progressively different times during the month. The phases and their positions relative to the Sun in the sky are given below: New Moon : With the Sun in the Sky Waxing Crescent : between 0° and 90° East of the Sun First Quarter : About 90° East of the Sun Waxing Gibbous : between 90° and 180° East of the Sun Full Moon : Opposite the Sun in the sky (180° East and West of the Sun) Waning Gibbous : between 180° and 90° West of the Sun 3rd (Last) Quarter : About 90° West of the Sun Waning Crescent : between 90° and 0° West of the Sun       Phase 1 - New Moon - The side of the moon that is facing the Earth is not lit up by the sun. At this time the moon is not visible.   Phase 2 - Waxing Crescent - A small part (less than 1/2) of the moon is lit up at this point. The part that is lit up is slowly getting bigger.   Phase 3 - First Quarter - One half of the moon is lit up by the sun at this point. The part that is lit up is slowly getting bigger.   Phase 4 - Waxing Gibbous - At this time half of the moon is lit up. The part that is lit is slowly getting bigger. Waxing means to slowly get bigger.   Phase 5 - Full Moon - The side of the moon that is lit up by the sun is facing the Earth. The entire moon is lit up at this point.   Phase 6 - Waning Gibbous - The moon is not quite lit up all the way by sunlight. The part of the moon this is lit is slowly getting smaller. Waning means to slowly get smaller.   Phase 7 - Last Quarter - Half of the moon is lit up but the sun. The part that we can see lit up is slowly getting smaller.   Phase 8 - Waning Crescent - A small part of the moon is lit up at this point. It is getting smaller by the minute. FUN FACT: Did you know that a full moon can happen twice in one month? When this happens, the second full moon of the month is called a Blue Moon! One possible explanation for this phenomenon is that the phases are caused by clouds covering up parts of the Moon. This idea is quickly defeated when one observes a non-full Moon when there is not a cloud in the sky. Plus it's highly unlikely that clouds would cover the Moon the same way every month. Another explanation is that the Moon is being covered by Earth's shadow in some kind of partial eclipse. Two things here don't make sense. One is that the Moon is Full when it's opposite the Sun in the sky that should be when it is covered the most by any Earth shadow. Also we would predict to see shapes where the Earth's shadow has taken only a tiny slice out of the Moon, and another where it has taken a sizeable slice. Neither shape is seen as part of the normal phases. The answer is that the Moon is always illuminated by the Sun and that as it orbits Earth we see different amounts of the part of the Moon in sunlight and the part of the Moon in darkness. First Note: Earth appears to have phases as seen by the Moon, but they are the exact opposite phases as those seen of the Moon by Earth inhabitants at the same time. Second Note: The Moon always shows the same face to Earth. Thus, it makes one complete spin on its axis per orbit around Earth. -> Synchronous Rotation. Eclipses (click for pictures)   We live in a special time in the history of the Earth-Moon system. In the present epoch the Moon is at sufficient distance to appear in the sky exactly the same angular size as the Sun. The Sun is 390 times bigger than the Moon, but the Moon is 390 times closer. This means that when the Moon moves in front of the Sun to eclipse it it does so exactly. In the past the Moon was closer and in the future the Moon will be further away. Eclipses occur when the Earth, Moon, and Sun are lined up to allow one body to fall into the path of the other's shadow. An eclipse of the Sun occurs when the Moon is between the Earth and Sun and it's shadow touches the surface of Earth. A Lunar Eclipse occurs when the Moon is opposite the Sun in the sky and passes into Earth's shadow. Why don't these eclipses happen every month at New and Full Moon? Because the Moon's orbit around the Earth is tilted with respect to the ecliptic by about 5°. So most of the time they miss each others shadows. Solar Eclipses    (click) There are two basic types of Solar eclipses: Annular Eclipses: these occur when the Moon is at it furthest distance in its elliptical orbit and appears slightly smaller in angular size than the Sun. Thus it does not cover the Sun completely but leaves a ring (annulus) around it during the eclipse. Total Eclipse: These occur when the Moon completely covers the disk of the Sun. It lasts for only a few minutes as seen from any given location. The Shadow that is moving across the Earth is only a few hundred miles in diameter and moving at a couple of thousand miles an hour across Earth's surface. Those places not inside the direct path of the shadow may see some kind of partial eclipse. During totality the Chromosphere and Corona of the Sun can be seen. Normally they cannot because they are too dim compared to the Photosphere. Lunar Eclipses When the Moon is eclipsed it is visible from everywhere on Earth. It lasts for many hours as the Moon first moves into the Penumbra of Earth's shadow and then finally into the Umbra. It often turns a deep red color because some light is still reaching it. This light is light being lensed by Earth's atmosphere and is red for the same reason that sunsets are red. Time Keeping 1 Day = 1 Diurnal Cycle of the Sun = 24 hours ~ 1 rotation of the Earth 1 Month = 1 Synodic Cycle of the Moon. ~ 30 days ~ 1 revolution of the Moon 1 Year = 1 Revolution of Earth about the Sun = 365.25 days Chapter 5 The Shape and Size of Earth What is the Shape of the Earth? Looks Flat - The closer to Earth's Surface you get the more and more you cannot discern the curvature and it looks flat. Evidence for Curvature - As ships head out to sea they don't disappear all at once, but rather their masts disappear last. - The Sun's position in the sky is different from different locations on the same day. - As you move north or south you can see different stars that were previously hidden by the horizon. Not possible on a flat Earth. Evidence for Spherical - The Moon and the Sun are circular in projected appearance (the Moon's Phases give away its spherical shape), Why not Earth? - Earth's shadow on the Moon during a lunar eclipse is circular. Eclipses happen at all altitudes so Earth must be Spherical (Aristotle ~300 B.C.) What is the size of Earth? Eratosthenes figures it out. Reads a report about the Sun being seen at the bottom of a well and no shadows being cast at noon on the Summer Solstice in Syene. He never observed this to happen in Alexandria. Must be due to Earth's curvature. Meausure the angle of the shadow made by objects in Alexandria, on June 21st: 7° Measure the distance between Alexandria and Syene: 500 Stadia = 800 km (hires a man to pace this out) The ratio of the angle to that of a full circle would be equivalent to the ratio of the distance between Alexandria and Syene and the Circumference of the Earth: 40,000 km. Real Answer: 40,030 km   Motion of the Planets in the Sky (click) After you observe the sky long enough you will notice that there are few special "stars". They do not twinkle like the other stars, and they do not keep the same annual rhythms. These were known as the wanderers by the Greeks, or Planets. There are 5 naked eye Planets: Mercury, Venus, Mars, Jupiter, and Saturn. Named after the Olympian Gods of classical mythology. The planets Uranus, Neptune, and Pluto were not discovered until well after the invention of the telescope. Days of the week are names after the wanderers: - Sunday: The Sun - Monday: The Moon - Tuesday (martes): Mars - Wednesday (miercoles): Mercury - Thursday (jueves): Jupiter - Friday (viernes): Venus - Saturday: Saturn The planets are known as wanderers because they change their positions with respect to the stars but all with different periods. The planets all wander through the Zodiac. They do this because all of the planets in our solar system orbit the Sun in a plane. Their individual planes are all a tiny bit different from ours. So as seen from Earth they will all be very close to the ecliptic plane (Earth's orbit). If they were all in exactly the same plane they would all lie exactly on the ecliptic. The planets' motions are sufficient slow that you need to watch over the course of several days/weeks/months to notice them. So they still always rise in the East and set in the West. Their general motion through the Stars is from West to East. This is because they are all orbiting the Sun in the same direction as Earth is. Occasionally they move East to West through the stars for a few months. This is called retrograde motion. The planets do not actually change their directions in their orbits. Rather it's an optical illusion caused when Earth passes the planet by. The majority of ancient Greek thinkers preferred a model of the Universe with the Earth at the center: Geocentric. Ptolemy devised the best geocentric model which accurately explained and predicted planetary motion. Used Epicycles to explain retrograde motion. The model stood for 1500 years. Chapter 6 The History of Astronomy Early Timeline Ancient Astronomy ~17,000 BC, Lascaux cave paintings depicting celestial events Egypt The Pyramids built with celestial alignments accurate to within a few minutes of arc. Used Diurnal Motions as a clock Babylonia Developed sexagesimal (60) counting system: 360 degrees in circle, 60 minutes per hour, 60 seconds per minute, etc. Compiled tables of planetary motion Predicted eclipses No understanding of why events occurred, no pictures of orbits, no geometry! China Well-preserved historical records dating back 3000 years Oldest records of comets, eclipses, sunspots, etc. Astronomy tied to political bureaucracy and functioning of government Decline in the importance of Astronomy after 1200 AD Mayans Developed a complicated and extremely accurate calendar precise tables of for motions of Moon and Venus predicted eclipses All cultures on Earth have made some understanding of the motions of the heavens. But the contribution by the Greeks of the use of a scientific reasoning was special and led to great discovery. The Greek Contribution  Pythagoras of Samos (circa 580 - 500 BC) Mystical understanding of the Cosmos using mathematics Numbers as a bridge between humans and the divine mind Invented the roots of the western musical scales Believed in a spherical Earth, by reasoning alone and not with any evidence whatsoever. Postulated that Sun, Moon, and planets move in concentric circles Believed the distances were in ratio with musical harmony: Music of the Spheres Plato (circa 428 - 348 BC)   Student of Socrates (c. 470 - 399 BC) Ascendency of the role of deductive reasoning. Believed sensory experience to be subjective, that pure thought was preferable to experiment. Urged astronomers to think about the heavens, but not to waste their time observing them. Philosophy was the work of the mind Manual Labor was for slaves The Physical World is merely a shadow of the perfect world of the forms The Pythagorean solids and their correspondence to the 5 Elements: Fire - tetrahedron (4 sides, triangles) Earth - cube (6 sides, squares) Air - Octahedron (8, triangles) Water - Icosahedron (20, triangle) Cosmos - Dodecahedron (12, pentagons) : knowledge of this shape suppressed by Pythagoreans Eudoxus (circa 408 - 356 BC) Devised a model of the Universe as an answer to a challenge put forth by Plato. Universe consisting of nested spheres with the planets attached Retrograde Motion a result of planets being attached to smaller spheres affixed to the larger spheres: epicycles Aristotle (384 - 322 BC)  Student of Plato's Academy Worked in almost every field of known science and philosophy! Believed that every effect has a cause Important innovation: Universe can be described by natural laws inferred by rational thought Invented a system of Physics: mostly quite wrong, but had a strong common sense appeal - suffered from lack of experiment in some cases (Pythagorean bias) Founded science of mechanics (physics of motion) developed the idea of force, impetus theory of motion (wrong, but still widely held even today) Thought force was required to keep a body in motion Separate laws for Earth and the Heavens Gravity on Earth but not in Heavens Natural motion is straight lines on Earth, circles in Heaven Reasoned that Earth was spherical based on observations of Earth's shadow on the moon, the fact that different stars can be seen farther south than Greece, etc. Believed in a Earth-Centered Universe with the Heavens rotating above - Geocentric Heraclides (circa 388 - 310 BC) Proposed that Earth is rotating to explain the daily motions of the heavens. Proposed that Mercury and Venus orbit the Sun because they never get very far from the Sun His ideas were soundly rejected by the Aristotle school of thought Aristarchus of Samos (circa 310 - 230 BC) Measured the relative sizes and distances to the Moon and Sun Found the Sun to be Bigger than Earth! Reasoned that the Sun rather than Earth is the center of the Universe and the Earth is one of the planets His ideas again rejected by Aristotle, no parallax of stars Eratosthenes of Cyrene (276 - 194 BC) Director of the Library of Alexandria Read an account of the Sun's path on the Summer Solstice in the southern frontier city of Syene. He realized that Earth must be curved and correctly calculated its size Hipparchus of Rhodes (190 - 120 BC) Synthesized Babylonian and Greek data with new Greek geometrical models Constructed the largest star catalogs in existence at the time Discovered the precession of Earth's axis Refined Aristarchus' measurements Measured the length of the year to an accuracy of 6 minutes! Devised a system of brightness for the stars: magnitudes: still in use today (much to the chagrin of modern astronomers) Ptolemy (circa 140 AD) Claudius Ptolemaeus, a.k.a Ptolemy, was also a director of the Library of Alexandria in his time. He is sometimes considered the last great natural philosopher of classical times.  He put together a model of the Universe that did not change much for 1500 years. Ptolemy used the collected observations of Hipparchus to build his model and to measure the parallax of the Moon, and thereby make another measurement of its distance. His model was marked by using the geocentric model first developed by Eudoxus. He considered a heliocentric model, like that proposed by Aristarchus, but immediately rejected it based on Aristotelean physics. He made alterations to the geocentric model, added some epicycles within epicycles in order to make the model explain all of Hipparchus' data. He also offset some of the spheres so that they were not necessarily concentric with Earth. The most important thing about this model was that it was able to predict the positions of the planets with great accuracy (at least to the level that people were able to measure in those times). The model contained no explanation for how or why these motions occurred (it had no physics). In subsequent centuries the alterations made to the model would be to add more epicycles into the model. This was done primarily by Arabic astronomers in medieval times. In the end some planets would have as many as 80 epicycles in order to be able to properly predict where they would be. Ptolemy also codified the pseudoscience of astrology into the form which is still in use today. That just goes to show that great genius is no guarantee against being dead wrong. Astrology In the beginning Astrology and Astronomy were one and the same. The basic tenets of modern Astrology (Ptolemy's system) are that a person's character and destiny can be understood from the positions of the Sun, Moon, and Planets at the moment of his/her birth. Astrologers use a chart called a horoscope and claim to be able to predict and explain the course of life and to help people, companies, and governments with decisions of great importance. Scientific investigations of horoscope predictions find them to be no better than random guessing. Furthermore horoscopes tend not to be predictions at all but rather just advice. The advice is clothed in such vague language as to make an interpretation in hindsight seem as if the horoscope had actually predicted something. Sun sign descriptions of personality are so general that any person can identify some of themselves in the description. Read a couple and figure out the percentage of the description that is actually fitting. Typically no better than 50%. Random guessing again. Skeptical Questions for Astrology: What is the likelihood that 1/12th of the world's population is having the same kind of day? If astrologers are as good as they claim, why aren't they richer? Are all the horoscopes done before the discovery of the three outermost planets incorrect? Why do different schools of astrology disagree so strongly with each other? If the astrological influence is carried by a known force, why do the planets dominate? If astrological influence is carried by an unknown force, why is it independent of distance? If astrological influences don't depend on distance, why is there no astrology of stars, galaxies, quasars, etc.? Why can twins have different fates?   Assignment:  Chapter 4, 5, and 6 Notes on chapters 4,5,6 What are the phases of the Moon? When do eclipses happen? What are the two types of eclipses and explain each. What is the shape of the Earth? What is the size of Earth? What did the Greeks call the Planets? ______________Why? _______________________________________ The days of the week are named after them, what are they? Sunday Monday Tuesday Wednesday Thursday Friday Saturday What is retrograde motion? What does Geocentric mean? What happened in 17,000 BC? Briefly describe what each of these people contributed. Pythagoras of Samos Plato Eudoxus Aristotle Heraclides Aristarchus of Samos Eratosthenes of Cyrene Hipparchus of Rhodes Ptolemy What is your astrological sign? What is your horoscope for today?  Lunar Puzzlers (Hot Science)  Click on and answer the  4 questions. How did you do?  Test on chapters 4/5/6 Chapter 7 The Islamic Contribution to Astronomy After the Library of Alexandria was sacked in 5th Century AD and the Roman Empire collapsed, the knowledge of the ancient Greeks and their scientific tradition was lost. Islamic scholars salvaged what they could from the dying Hellenic culture and created their own center of knowledge in Baghdad (in modern day Iraq). They built a library that rivaled that in Alexandria. They combined the knowledge of the East and the West. Made great mathematical contributions by inventing Algebra. Made careful observations of the heavens. During this time the geocentric model of Ptolemy was still used but the Arab scholars found it necessary to continue to modify the model adding epicycle within epicycle. At one point the geocentric model had as many as 80 epicycles within epicycles. Quite ridiculous! When the Byzantine capital of Constantinople fell in the 15th Century AD many Eastern scholars fled into Europe and brought with them the knowledge they had been accumulating over the centuries. This return of Classical knowledge and tradition to Europe marked the beginning of its Renaissance after a long period of darkness.      Nicholas Copernicus (1473 - 1543) A Polish Catholic Physician and Lawyer. In his text, On the Revolutions of the Celestial Orbs he put forth a heliocentric model of the Universe, like the one Aristarchus had proposed some 2000 years earlier. The work was not published until Copernicus was on his deathbed in 1543. Sun at the center of the Universe Earth 3rd planet from the Sun. daily motions of the Sun and Moon were the result of Earth spinning. yearly motions of the stars and Sun are explained by the motion of Earth in a circular orbit about the Sun. retrograde motion of planets was simply the optical illusion of backward motion during the occurance of one planet being "lapped" by another. With the model Copernicus was able to calculate the relative spacing between the planets...  Click on below. Martin Luther described Copernicus as an "upstart astrologer". He cited biblical scripture where Joshua commands the Sun to stand still and not the Earth as disproof. In 1616 the Catholic Church place the work on a list of banned books, until all copies could be "corrected" by local ecclesiastical censors. It remained on this list until 1835. A recent survey of medieval texts found the censorship to have been ineffective. Only 60% of copies in Italy were censored and none had been in Iberia.Some of Copernicus' supporters suggested that Copernicus himself had never truly believed in the model, but found it more convenient for calculating planetary motions than Ptolemy's cumbersome geocentric model. Key Point Copernicus' model did not do any better at predicting the positions of planets than did Ptolemy's model, but it did just as well. This is mainly because Copernicus assumed that planetary orbits were circular. They are not. Also people stubbornly held onto Aristotelean physics. If the Earth moves why do the stars not exhibit parallax? Some scholars at the time suggested that perhaps the stars were so far away that their parallax could not be measured. Then there was the argument as to the fact that we do not feel the Earth move. How can it then be moving? It would take Newton to explain this. Thus Ptolemy's model still held sway for at least the next 50 years. But its time was at hand. Johannes Kepler (1571 - 1630) and Tycho Brahae (1546 - 1601) Born in Germany in 1571 Johannes Kepler was a Protestant in a land dominated by Catholic thought. He was sent to a Protestant seminary as a young boy. He was withdrawn and sad. But he found solace and joy in the study of Geometry. In the geometry of Euclid, Kepler believed he had glimpsed the mind of God. He eventually left the seminary and went off to study for the clergy. It was here that his teachers exposed him to the dangerous mysteries of Copernicus' heliocentric Universe. This idea resonated strongly with Kepler. The Sun was a metaphor for God in his mind and it seemed right to have the Universe revolve around it paying homage. Before becoming ordained Kepler took a job as a teacher in Graz, Austria. There he taught middle school mathematics. He was a terrible teacher, and his students payed his lectures little attention. It was while in the midst of one of his long dronings that an idea struck him. This idea would forever change the course of Astronomy. There were only 6 planets known in Kepler's time. He wondering why only 6? Why not 1 or 20? Why did they have the spacing deduced by Copernicus? There were known to be only 5 perfect solids, whose sides were regular polygons. Kepler's idea was that the two numbers must be connected. There are only 6 planets because there are only 5 perfect solids. He thought that the solids when inscribed or nested one within the other would specify the distances of the planets from the Sun. He believed that he had envisioned the invisible support structure for the planetary spheres. He called this revelation The Cosmic Mystery. In this connection he believed there could be only one explanation: The Hand of God, Geometer. Kepler tried and tried to build a model that would fit his idea of the nested solids to the spacings inferred by Copernicus. He could not. When he finally realized that it was simply not possible, he did what all good theorists do: he sought better data... Enter Tycho Brahae. Tycho was born of Danish nobility and was flamboyant, boisterous, and arrogant. He wore a golden nose, his original nose having been lost in a student duel over who was the better mathematician. His goal in life was to be the greatest naked eye observer that ever lived. He claimed to all that would listen that he was. He was right. Using his great wealth he designed instruments that were more accurate at measuring angles and positions in the sky than any other such device previously known. Tycho rejected the heliocentric theory on the basis that if it were true stellar parallaxes must be measured. Since not even he was capable of this he concluded that it must not be so. He preferred a hybrid model in which all of the other planets went about the Sun and the Sun went about the Earth. Despite the argument that had lost him his nose he was not a great mathematician and he knew it. Thus he was not fully equipped to make sense of the extremely accurate data that he had been amassing on the motions of the planets. The irony in this was that he had been appointed to the post of Imperial Mathematician in the court of the Holy Roman Emperor, Rudolf II. Tycho had heard of a brilliant young mathematician by the name of Kepler and invited Kepler to join him in Prague. In 1598 Kepler's school was closed by order of the local Catholic archduke and Kepler was exiled. He decided to take Tycho up on his offer. The two men were as different as night and day. Kepler was a monkish, pious, and scholarly country bumpkin. Tycho was a party animal, continuously surrounded by a rowdy entourage of revelers who often mocked poor Kepler. The two men distrusted one another. Tycho only gave Kepler little scraps of his data at a time and Kepler kept his findings a secret from Tycho. During one particular festivity Tycho was in the company of the Baron of Rosenberg. He had drank quite excessively and was in dire need to relieve himself. But he felt that it would be disrespectful to the Baron to excuse himself. So he held it... as a result he developed a nasty urinary tract infection and ignored his doctors' advise to lay off the excessive drinking and eating. In just a few short months he was dead. On his deathbed Tycho repeated deliriously to Kepler, "Let me not seem to have lived in vain...Let me not seem to have lived in vain." He did not. After Tycho's death Kepler inherited the sum of all Tycho's work. Tycho had data for the planets over the course of many years. The precision was exquisite. He used the same method as Copernicus to determine the distance of Mars from the Sun at various places in its orbit. He started with Mars, because its orbit was the one that did not fit his nested solids model the most. Much to his dismay this newer, and better data did not conform to his model either. After 3 years of intense mathematical calculations Kepler made a brave decision. He abandoned his idea and concluded that the planetary orbits were not circles afterall as has been assumed by everyone previous to him. The data simply did not support it. In fact the data outright demanded the correct answer: the planets orbit the Sun in ellipses. Kepler's work would eventually lead him to formulate 3 laws of planetary motion: 1. Planets move in elliptical orbits with the Sun at one focus of the ellipse.           The orbital speed of a planet varies so that a line joining the Sun and the planet will sweep over equal areas in equal time intervals. This means that a planet moves faster closer to the Sun and slower farther away. The amount of time a planet takes to orbit the Sun is related to its orbit's size, such that the period, P, squared is proportional to the semi-major axis, a, cubed: P2 a3 This last law is the one to remember. It is true for any object in orbit around another. The only thing that changes is the constant of proportionality (because it depends on the masses of the objects). For the planets, asteroids, and comets in our solar system the constant is the same. The best way to use it is in a ratio. You know that the Earth orbits the Sun in 1 year. We define the Earth's average distance from the Sun (93 million miles) to be one Astronomical Unit (1 AU) which is the same as the semi-major axis of the ellipse. So what is Jupiter's average distance from the Sun if its orbital period is about 11 years? Well, Kepler's 3rd law states that: P2 a3 or put another way P2 = ka3 Where k is the constant of proportionality, and is the same for Earth and Jupiter (and all the other planets in the Solar System). So we may write P2/a3 = k For both Jupiter and Earth. So we have P 2/a 3 = k = PJ2/aJ3 Plugging in what we know gives (1 year)2/(1 AU)3 = (11 years)2/aJ3 Algebraicly rearranging the equations says that aJ3 = (11 years)2 x (1 AU)3/(1 year)2 And so, doing the arithmetic gives a = (11 AU)2/3 = 5 AU Kepler now wondered what would cause the planets to slow down in their orbits as they move away from the Sun and speed up as they approach the Sun. He suggested that there was some force akin to magnetism (which was known at the time) that the Sun exerts on the planets. Kepler was foreshadowing the discovery of gravity by Isaac Newton as that force.  Galileo Galilei (1564 - 1642) Kepler's interpretation of Tycho's data absolutely insisted that the heliocentric model was more correct than the geocentric model of Ptolemy. But most people in their time were not so willing to accept such mathematical interpretations and required more understandable proof. The Italian scientist Galileo Galilei would give them proof undeniable. Galileo was a contemporary of Kepler's and the two corresponded with each other over their respective discoveries. Galileo had seen a Dutch spectacle maker demonstrate a new instrument which he called a telescope. Galileo built his own telescope and made some minor modifications. He turned the telescope to the stars and again the Universe was forever changed. Through his telescope Galileo observed: that the Moon was marked with great craters and mountains and was not the perfect orb it was believed to be. sunspots on the Sun that he watched go around the Sun and concluded that the Sun must rotate. He calculated the rotation period of the Sun. This proved the Sun was also not the perfect orb it was believed to be. Saturn to have what he called ears. His telescope was not powerful enough to resolve these ears into the beautiful rings that surround Saturn. that the Milky Way was actually a vast cloud of innumerable stars. that Jupiter had 4 moons that circled it and not the Earth or the Sun! These 4 largest moons of Jupiter (Ganymede, Callisto, Europa, and Io) are now known as the Galilean Moons. that Venus went through a full cycle of phases just like the Moon. Something impossible in Ptolemy's geocentric model. The observation of Jupiter's moons showed that at least some objects did most definitely not orbit Earth. But the observation of Venus' phases proved that it must orbit the Sun.           If Venus orbits the Sun, then why not all the planets? This was the death-blow to the geocentric model. Galileo published his observations and interpretations touting the heliocentric model widely. He made no attempt to hide these discoveries, and it got him into a lot of trouble. In 1633 Galileo was compelled to stand trial for "vehement suspicion of heresy" by the Catholic Church. The Church had liked the idea of a Universe centered on Earth. It had taught the Ptolemaic model as the correct one reinforced by biblical scripture. Galileo was threatened with excommunication and death if he did not recant his claims. Eventually he capitulated. There is a story (likely apocryphal) that when Galileo recanted his belief that the Earth went around the Sun to the Church court he muttered under his breath so that only those nearest could hear him say, "and yet, it moves." Galileo was placed under house arrest for the remainder of his life. It was hardly a punishment. He continued to do physics experiments involving rolling balls on inclined surfaces, studying the motions of a pendulum, and dropping balls of different masses to see which would fall fastest. The results of his experiments and his interpretations would later lead Newton to reinvent physics and once again change the Universe. Chapter 8 Isaac Newton (1642 - 1727)  (click on) Isaac Newton was born in an English village the year that Galileo died. His were very humble beginnings, and yet he would rise to become arguably the greatest scientist the world has ever known. When he was 20 years old he bought a book on astrology at a fair, "out of curiosity to see what was in it." He came upon a figure in the book that he did not understand because it involved trigonometry and he was ignorant of trigonometry. So he bought a book on trigonometry. When he couldn't follow the geometrical arguments in that book he bought himself a copy of Euclid's Elements of Geometry. Two years later he invented differential calculus. In 1666 he was an undergraduate at Cambridge University when an outbreak of plague forced him to spend a year away in the isolated village of Woolsthorpe, where he had been born. In that year he invented differential and integral calculus, made fundamental discoveries on the nature of light, and began to think on the law of Universal Gravitation. It was quite a year. Newton's Laws of Motion In 1687 Netwon finally published his Principia were he laid out his laws fundamental laws of motion. The Law of Inertia: If the sum of the forces on an object add to zero then the object's velocity will remain constant. "An object in motion tends to stay in motion, and an object rest tends to stay at rest." do nothing to an object and it will keep doing what it has been doing all along. inertia is the idea that an object will resist a change in its motion (either making it move or trying to stop it from moving). Note: since neither speed nor direction of motion changes that we always have motion in a straight line when there are no forces. F = ma acceleration experienced by an object is directly proportional to the amount of force exerted on it. The constant of proportionality is the object's mass. This is how mass is essentially defined. Sometimes it's refered to as inertial mass. Action and Reaction: When two bodies interact, they create equal and opposite forces on each other. (Examples: Two gravitating bodies exerting the same gravitational force on each other, two skateboarders pushing on one another, a ball bouncing off the wall, astronaut throwing a hammer, etc...)  Circular Motion The law of inertia tells us that if there are no forces acting on an object then its motion is in a straight line. So how do we produce circular motion, like that of the planets in their orbits? We have to apply a force. The force that we need to apply must constantly change the direction of of the object's motion without altering the tangential speed of the object. We can show this with an object tied to the end of a string. If we swing the object around in a circle above our heads the force that is causing the object to go around is the tension in the string. You can feel the tension as you swing the the object. If we were to suddenly cut the string the object would continue off on a tangential line from the spot it was released. It will not continue on in a curved path. Click Below The force that keeps planets, moons, etc. in orbits is gravity, the natural attraction of all matter to other matter. We can visualize how to put something in orbit by imagining firing a canonball from a very high mountain. The greater the initial velocity we give the ball the farther down range it will go before falling to the Earth. If we get it at just the right speed it will continue to fall toward the Earth, but the Earth's curvature will continue to curve away from it and it will make a full circle and eventually hit the back end of the canon. So an object in orbit is indeed experiencing gravity. For example the Space Shuttle when it is in orbit around the Earth is always falling toward the Earth, but it is also heading tangentially at just the right speed to stay in a circle (or ellipse). So it is always under the influence of gravity. The astronauts appear weightless because they and the Shuttle are all falling together at the same rate. The Universal Law of Gravity Newton made the connection between the "magnetic" force that Kepler had supposed caused his 2nd law implied and the everyday force of gravity. The old story goes that one day Newton was out sitting under an apple tree looking at the Moon. The story goes that when he saw an apple fall he wondered if the force that was keeping the Moon in orbit around the Earth was the same force that made the apple fall to the ground. That would mean that the Moon is always falling toward Earth in the way we described above. He also then reasoned that it must be gravity that holds the Earth and planets in orbit about the Sun. So we are always falling toward the Sun. He studied Kepler's 3rd law of planetary motion and his own laws of motion to come up with a Universal Law of Gravitation. Given two masses, m1 and m2 the force between them is given by F = - Gm1m2/r2 Where r is the distance between the two objects and G is a constant found empirically, G = 6.67 x 10-11 m3*g-1*s-2. By Netwon's 3rd law this is the force felt by both objects. The negative sign indicates that the force is attractive it draws the two bodies together. For example the force of attracttion that your body feels toward the Earth is the same force of attraction that the Earth feels toward you. But since Earth is way more massive than you its acceleration is much, much, much less than yours. You can see this by relating the law of gravitation to Newton's second law. F = - GM myou/r2 = - myouayou = -M a So your acceleration toward Earth is ayou = GM /r2 And the Earth's acceleration toward you is a = Gmyou/r2 And so the ratio of Earth's acceleration to yours is a /ayou = myou/M Which is a very small number. And so Earth doesn't react much to your presence, but you react alot to Earth's. Kepler's 3rd Law Netwon also found that he could derive Kepler's 3rd law using his new fangled-dangled invention: calculus. In doing so, he realized that he could figure out what that constant of proportionality was in Kepler's 3rd Law. It turns out that it depends on the masses of the two objects in question. He found the general form to be P2 = 4 2/G(m1 + m2) * a3 So the constant k = 4 2/G(m1 + m2). IMPORTANT: If m2 << m1 then we may ignore m2 such that m1 + m2 m1 then the relation becomes P2 = 4 2/Gm1 * a3 This is the case for all the planets in the solar system compared to the mass of the Sun and likewise for most of the moons in the solar system compared to their mother planets. This fact can be used to measure the mass of the Sun. For all planets in the Solar System we may write P2 = 4 2/GM * a3 Let's rearrange the equation in the usual way to isolate the quantity that we want to know. M = 4 2/G * a3/P2 We know all these values for Earth and if we plug them in we find that M = 2 x 1030 kg Surface Gravity Newton spent many extra years thinking about a certain problem involving the gravity of a spherically symmetric mass. He believed that the body would behave as though all of its mass was concentrated at the center. But in order to prove this he would need to invent integral calculus. Indeed his intuition was correct. That means if you have mass, m, and are standing on the surface of a planet with Mass, M, and Radius, R, then the force of gravity acting on you is F = -GMm/R2 . Now notice also that it is true by Newton's 2nd Law that F = -GMm/R2 = ma Simplifying the expression... a = -GM/R2 This says that the acceleration you feel due to the planet is independent of your mass. That's just what Galileo showed in his famous experiment of dropping canon balls from the leaning tower of Pisa. NOTE: the force you feel due to gravity is your weight Escape Velocity If you wish to escape from the surface of a gravitating object there is a special velocity you must have in order to accomplish this. It's called the escape velocity. The best way to understand this is to think in terms of energy. In order to be able to escape from a planet you want to have an initial velocity that will make your total mechanical energy be at least zero or greater (unbound). Recall that the total mechanical energy is written as E = KE + PE In our initial system we have KE = 1/2 mvesc2, and PE = -GMm/R. We want E to at least be equal to zero to be unbound. So we may then write E = 1/2 mvesc2 - GMm/R = 0 Let's now solve this for the escape velocity. 1/2 mvesc2 = GMm/R So, again we see that the mass, m, of the object is unimportant to the calculation. vesc = (2GM/R)1/2   An interesting idea that was raised not long after Newton's time was that if an object were to have just enough mass enclosed in a small enough radius the escape velocity would be greater than the speed of light, and then not even light could escape the surface of this object. It was then known as a "Black Star". Today this is rather similar to the idea of a Black Hole. Planetary Orbits Planetary orbits were found by Kepler to be ellipses. But Newton found that they are even more general than ellipses, they are conic sections. How the Moon Effects Tides http://home.hiwaay.net/~krcool/Astro/moon/moontides/ Tides:  How the Mood Effects Ocean Tides  (Click) Because the force of gravity is weaker with increasing distance the gravitational pull an extended object will feel will be different across its length. This differential gravity is called a tidal force. The Moon exerts a differential pull on Earth and this is the cause of the tides on Earth. The side closest to Earth is accelerated toward the Moon the most the center a little bit less and the far side of Earth less still. This causes the shape of Earth to be squished out like a football.Since the rock of Earth is less likely to distort, the oceans do most of the distorting. High tide occurs when the Moon is overhead or at the nadir of its overhead position. Likewise, low tide is when the Moon is 90° from overhead. There are two high tides and low tides every day. The Sun also contributes to this, but the Sun's tidal distortion on Earth is half that of the Moon's because of its distance. The maximum tides occur when the Earth, Sun, and Moon are all in a line (new and full Moon). The minimum tides occur when the Moon is in either quarter phase. The Earth will one day reach a similar state. Then the day will be as long as a month, which will also be longer than the current month because the Moon will be farther away. The Moon's angular size in the sky will be smaller and there'll be no more total solar eclipses. Also Earth will show only one face to the Moon just as the Moon currently does to Earth. This will actually never happen because the Sun will die out and destroy Earth first.   Assignment: Chapter 7 and 8 Astronomy HW #4 Notes on chapters Briefly write about Nicholas Copernicus Johannes Kepler and Tycho Brahae Galileo Galilei Isaac Newton Explain the following: circular motion Universal Law of Gravity Kepler’s 3rd Law Tidal Force Project #2:  Scientific Contributor Choose 1of the following & write a 2 page paper/MLA, Works Cited ·        Pythagoras of Samos (circa 580 - 500 BC) ·        Plato (circa 428 - 348 BC) ·        Eudoxus (circa 408 - 356 BC) ·        Aristotle (384 - 322 BC) ·        Heraclides (circa 388 - 310 BC) ·        Aristarchus of Samos (circa 310 - 230 BC) ·        Eratosthenes of Cyrene (276 - 194 BC) ·        Hipparchus of Rhodes (190 - 120 BC) ·        Ptolemy (circa 140 AD) ·        Nicholas Copernicus (1473 - 1543) ·        Johannes Kepler (1571 - 1630) and Tycho Brahae (1546 - 1601)                  Galileo Galilei (1564 – 1642)                  Isaac Newton (1642-1727)             Chapter 9 Light Radiant energy Interacts with matter via either: Emission: Light is released Absorption: Light is captured Transmission: Light is allowed to pass through Reflection: Light is bounced away Moves through a vacuum a constant speed, c. Exhibits Wave Nature Diffraction Exhibits Particle Nature Reflection The waves consist of self-propagating, oscillating electric and magnetic fields. Electric Field -- the region in which electric forces can be observed, e.g. near an electric charge. As a field, it may also be viewed as a region of space modified by the presence of electric charges. Magnetic field -- a region in which magnetic forces can be observed. Magnetic fields are created by moving charges (current). Changing electric fields create magnetic fields, and changing magnetic fields induce changing electric fields. If a charge accelerates the electric field around it will change, creating a magnetic field, which as it forms and collapses with induce an electric field, and an Electromagnetic wave is born... Properties of waves Wavelenth = (greek "lambda") = distance from one crest to another. Typical units for are angstroms, 1 Å = 10-10 m = 0.1 nanometers (nm). Frequency = (Greek "nu") = number of crests/troughs passing some fixed point per unit time. Typical unit for frequency is hertz, 1 Hz = 1 s-1. [NOTE: -1 = 1/ = P = Period = length of time between the passing of one crest to another as seen from a fixed point] Speed: the speed, v, of a wave is the distance that a crest travels per unit time. We can write that in terms of wavelength and frequency as = v = c Where, c, is the specific value that we use for the speed of electromagnetic waves. It is a constant in empty space (a vacuum). c = 3 x 108 m/s Visible light is the light that human eyes are sensitive to. It comes in colors as seen when white light is passed through a prism and broken into a rainbow. Violet Indigo Blue Green Yellow Orange Red Different colors correspond to electromagnetic waves having different wavelengths ( ).             Wavelengths of the visible colors: Color (Å)   Red 7000 Yellow 5800 Green 5000 Blue 4800 Violet 4000 White Light: Is the presence of all the colors with equal intensities. If, for example, we had the presence of all the colors but red was more intense than the others then the light would look reddish-white, or pinkish.   The Electromagnetic Spectrum Visible light is only a very tiny fraction of the total amount of possible wavelengths that an electromagnetic wave can take on. The entire range of wavelengths (or equivalently, frequencies) is referred to as the electromagnetic spectrum. Name (meters)   Gamma-rays < 10-11 X-rays 10-11 - 10-8 Ultraviolet (UV) 10-8 - 4 x 10-7 Visible (Optical) 4 x 10-7 - 7 x 10-7 Infrared (IR) 7 x 10-7 - 10-3 Microwave 10-3 - 10-2 Radio 10-2 - 104 + Energy Carried by Electromagnetic radiation Light can behave as discrete particles: Photons Photons are little "wave packets" of energy Collectively, lots of photons having the same color ( ) make up an electromagnetic wave, with wavelength . White light is then made up of equal numbers of photons of all wavelengths. Shorter wavelength radiation has more energy than longer wavelength radiation. X-rays are more energetic than Microwaves. Brightness (intensity): a measure of the amount of energy being received by an observer. Can be thought of as the number of photons (the greater the number the greater the brightness) or the amplitude of the electromagnetic waves.   Putting it Together Three kinds of spectrum from matter are: Continuous Spectrum: typically thermal radiation from opaque objects Emission Spectrum: emitted light of specific energies from a diffuse gas Absorption Spectrum: light of specific energies absorbed from a continuous spectrum by an intervening diffuse gas. Doppler Effect We can measure the velocity of an object by analyzing the apparent wavelengths of spectral lines from it. Objects in motion compress the light waves in front of them making them appear more blue (blue shift), the light waves behind are stretched out and appear more red (red shift). Can calculate the velocity of motion along the line of sight: / 0 = v/c Where c is the speed of light, 0 is the wavelength of the light as seen at rest, and is the measured change in wavelength. This is extremely important in astronomy. We can measure the velocities of stars with respect to us. We can measure their rotational velocities. We can measure their speeds of orbit in binary systems. Plus we can measure their change in velocity caused by a planet in orbit around them. What can you learn from light? Breaking light from an object into a spectrum can tell you: The Chemical Composition The Temperature The Velocity along the line of sight Chapter 9 Questions What are the four ways in which light interacts with matter? Define the following: electric field Magnetic field Wavelength Frequency Speed Visible light What are the visible colors? What is the electromagnetic spectrum? Name the wavelengths? Do shorter wavelengths have less energy than longer wavelengths? What are the three kinds of spectrum from matter? What can you learn from light? What is white light? What are the many ways in which astronomers analyze light?   Chapter 10 Telescopes Click on for history: http://www.omni-optical.com/telescope/ut104.htm   Analysis of light is by far the major way in which astronomers gather information about the Universe. So, we need to collect as much as possible and study it in great detail. Use telescopes to gather more light than our eyes can, and to provide greater clarity. We record and measure light with electronic detectors. Use spectrographs, etc. to obtain more information about the physical conditions from which the light escaped. Study the entire electromagnetic spectrum -- not just visible light. Use radio and space telescopes, etc. Use computers for detailed, quantitative analysis Purpose of Telescopes The primary purpose of a telescope is to collect more light. The secondary purpose of a telescope is to provide greater resolution Space Telescopes There are several advantages to having telescopes in space. There is no distortion or blurring by the atmosphere of Earth. Telescopes can reach their diffraction limit. The telescope mirrors do not flex under their own weight as they do on the ground. The sky is darker. No scattered light from nearby human populations or from the Sun. The atmosphere also glows at certain wavelengths, especially in the infrared. The infrared sky is very bright. You can see ultraviolet, x-rays, gamma-rays, and infrared light blocked by the atmosphere. Even at optical wavelengths the atmosphere absorbs some light.   Hubble Space Telescope:  http://hubble.nasa.gov/index.php  (click on) Answer questions   Hubble Telescope Who is the Hubble Telescope named after? ______________________________ What is the Hubble Telescope and what does it do?   When was the Hubble launched?  _____________________________________ What is Hubble’s orbit around earth? __________________________________ How many miles above the earth does the Hubble orbit?  __________________ Who is the NASA administrator? _____________________________________ When will the next service mission be sent?  ____________________________ Describe what will be accomplished on the service mission.   Who will be making the trip to service the telescope?   What two new instruments will be in stalled?            Where is Hubble’s location right now?  Latitude __________Longitude ________             Altitude __________________ What is the size of the Hubble?  _______________________________________ How many miles does the Hubble travel each year?   _______________________ Which space center performs the daily orbital operations, serving mission development and overall management of the Hubble Program   How does the Hubble take pictures to send to mission control?       16.  Are the colors in Hubble images the colors we’d see if we were able to visit the imaged objects in a spacecraft? Explain   Detectors Astronomers no longer use their eyes to record images. After the invention of photography in the 1800s astronomers developed photographic plates. These were glass plates that had photosensitive emulsions on them that would be placed at the focus of the telescope. Light was then allowed to collect on the plates for long exposure times. The plates were then developed just like photographs still are today. Today, we no longer use photographic plates. We now use CCDs (Charged-Coupled Devices). They are solid-state semi-conductor chips that work on the principle of the photoelectric effect discovered by Einstein. Photons can knock electrons loose when they collide with certain elements. These loose electrons created a charge that we can measure. CCDs are used in video and digital cameras. Science grade CCDs have arrays of pixels of 2048 x 2048 or more. Each pixel stores electric charge in direct proportion to the amount of light that has been incident upon it. CCDs have many advantages: Linear response: double the exposure time or star brightness, double the charge Extremely sensitive: up to 80% of photons are detected Digital Output: analyze with computers Wide dynamic range: very faint or bright stars are measured accurately.   Chapter 11:  The Solar System Mercury: The Messenger Planet #1 from the Sun; 0 moons. Difficult to study: always near the Sun in the sky. Sets or rises within 1 to 2 hours of the Sun -> blurred images since light is traveling through lots of atmosphere. The rotation rate was finally measured with Radar. "Day and Night" cycle on Mercury = 176 days (88 consecutive days each of sunlight and darkness). The planet spins 3 times for every 2 orbits. Tidal friction brings the planet into synchronous rotation, but elliptical orbit keeps it from being 1:1. The orbital period is 88 days. Because of the orbit it is possible for the Sun to appear to move West to East for a brief period in the orbit. Almost no atmosphere. Planet not massive enough to retain atmosphere, and too close to the Sun which heats gases to enough energy so that it can escape from the surface. Without an atmosphere to circulate heat around the surface the temperatures are very extreme. Daytime, T = 430°C. Night, T = -170°C Mariner 10 (1974/5): flew past Mercury 3 times. Photos reveal the surface to be heavily cratered like the Moon. There are few if any uncratered Maria such as those on the Moon, however. There is no evidence for plate tectonics. Seems to be a geologically inactive world today. Not massive enough to generate sufficient heat in core, too small to retain any heat produced. Interior structure inferred from density and mass. Mass measured by encounter of Mariner spacecraft with the planet. Recall that with Kepler's 3rd law one can measure the mass of planet by the orbital properties of a satellite. Venus: Goddess of Love Planet #2 from the Sun; 0 moons. Shrouded in highly reflective clouds: bright "evening (or morning) star". Also relatively close to the Sun in the sky. Clouds are composed of sulfuric acid. Thick Atmosphere: (90 times Earth's surface pressure!) 96% CO2, < 4% N2 (Earth: 79% N2, 20% O2) (Earth's CO2 is trapped in rocks and oceans) Temperature of surface: 480°C! Hottest planet, due to runaway greenhouse effect.: visible sunlight penetrates atmosphere atmosphere blocks infrared light surface heats up due to visible light; radiates thermal energy in the infrared Infrared trapped by the atmosphere -> Hot! If there were an increase in the CO2 (or other greenhouse gases) in Earth's atmosphere, the surface would heat up -> release more CO2 into atmosphere -> runaway greenhouse In 1990-1993 NASA's Magellan spacecraft orbited Venus taking detailed radar maps of the surface. 100m resolution! The spacecraft saw craters, volcanos, large plains, valleys. 2 large "continents" 2-3 km above plain, but crust consists of only 1 plate (thick crust). Planet is still geologically active! Russian spacecraft, Venera, landed on Venus and was destroyed promptly by the corrosive atmosphere. Has long retrograde spin period. Perhaps the result of a great collision with a large planetesimal in its early formation. Mars: God of War Planet #4, 2 tiny, irregular moons. Red appearance due to rust (iron oxide). Surface visible through thin atmosphere. Clouds of ice particles visible in atmosphere. Mars has polar ice caps (mostly CO2) that grow and shrink with the seasons. Thin atmosphere (1% Earth's): 90% CO2. Windy: major dust storms occur. Atmosphere thicker in the past -> more greenhouse effect -> warm enough for liquid water to exist on the surface. Some great catastrophe may have blasted away the atmosphere some 2-3 Billion years ago, or perhaps the atmosphere was slowly lost because the planet's surface gravity isn't strong enough to hold onto the thicker atmosphere. T = -130°C to 30°C : generally cold. Spacecraft (1960s - 1970s): saw craters, volcanos, canyons. No plate tectonics, planets seems geologically inactive. Amount of cratering indicates that erosion has not been at work for several billion years. Volcanic activity (Olympus Mons) may have continued up until 250 Million years ago, however. Volcanic activity rather light and does not help replenish the atmosphere. No planet-wide magnetic field. So likley no molten rock in interior. Ancient river beds! water was abundant long ago. Now it is believed to be frozen in a permafrost layer and in the polar ice caps. Mars Pathfinder (1997) and Mars Global Surveyor: flood plains, dried up lake beds, morning fog in valleys, etc. Two moons: Phobos and Deimos (Fear and Panic). Both irregular in shape because they are not massive enough to be self-gravitating. They are likley captured asteroids. They show some cratering. Phobos has cracks indicating that it was once struck so violently as to nearly break it in two. Life on Mars: Lowell's canals not real. 1976 Viking landers' tests were inconclusive. 1996: a meteorite from Mars is reported to have microscopic tube-like structures that look like fossilized tiny bacteria + several lines of chemical evidence. Very controversial. Extraordinary Claims Require Extraordinary Evidence Summary of the Jovian Worlds Assignments: Ch. 11 Notes on chapter Give facts about each planet in chart form Mercury Venus Mars Chapter 12 Jupiter: King of the Gods Planet #5 from the Sun, at least 28 known moons. Its radius is 11 times Earth's (R = 11R ), and one-tenth the size of the Sun (R = 0.1R ). Jupiter's mass is 320 times that of Earth (M = 320M ) and one-thousandth that of the Sun (M = 10-3M ). The planet is composed of mostly hydrogen and helium just like the Sun. Colorful bands parallel to the Equator. Lot's of swirls, spots: stormy. One storm, the "Great Red Spot" is 2 times the size of Earth, and has lasted for at least 300 years (Galileo saw it in his telescope). It's a gigantic hurricane. The planet appears oblate (squashed) this is due to rapid rotation (once every 10 hours!). Planet has very thin rings seen for the first time by the Voyager spacecraft, they lie at a radius of 1.8R . The spacecraft also witnessed lightening storms in the clouds. Spacecraft visits: Voyager 1 and 2 (1979), and Galileo (1996/1997 - today). Beautiful close-up views of the planets and its moons. The Galilean Satellites: the 4 largest moons of Jupiter each is larger than the Moon. Ganymede: The largest moon in the Solar System, it has an old, cratered surface. Callisto: Heavily cratered like Ganymede, lots of ice on the surface and frozen into the crust. Europa: Smooth surface with narrow, dark stripes running across, few craters. The surface seems to be fractured ice (water ice). Recent information from the Galileo spacecraft suggests that there is world-wide ocean of liquid water beneath the frozen surface. Life? Io: Erupting volcanos! The most geologically active body in the Solar System. The interior is molten, this is due to tidal forces which change throughout its elliptical orbit. A tortured world. The other known moons are all rather small; many are captured asteroids. Some have retrograde orbits.       Saturn: Father of the Gods (Father Time) Planet #6, 30 known moons. Saturn has a remarkably low density (0.7 g/cm3): it could float on an ocean of water! Like Jupiter and the Sun it is mostly composed of Hydrogen and Helium, with an Earth-like core. It also has atmospheric bands of clouds like Jupiter, but they are less colorful. It's most outstanding feature are its magnificent rings. The rings are mad of chunks of rock and ice. It is material that failed to coalesce into a moon, due to tidal forces of Saturn (inside the "Roche Limit"). The rings lie in the planet's equatorial plane (which is inclined 27°) to its orbital plane. This makes the rings appear "edge-on" twice per 29-year orbital period (e.g. in 1995). Only 4-5 of the rings are generally visible from Earth. There is a dark division between the 2 main rings ("Cassini's Division"). Spacecraft visits: Voyager 1 and 2 (1980): spectacular details! More than 100,000 "ringlets" only about 20 meters thick! Cassini spacecraft on its way... Saturn has more than 20 moons (new ones being discovered all the time). The largest of the Moons (visible from Earth in a small telescope) is Titan. Titan has a thick Nitrogen atmosphere (like Earth!). It also has the same chemical in smog pervading its atmosphere. There is some greenhouse effect that helps warm it. It's possible that there are methane lakes and a rain of organic materials onto the surface. Life? Uranus: God of Heaven Planet #7, 21 known moons This planet was not known to the ancients. It lies at the threshold of the human eye's brightness detection limit. It was discovered in 1781 by William Hershal a musician and part-time astronomer. It is smaller that Jupiter and Saturn, but still much larger than Earth. It is composed mostly of Hydrogen and Helium, plus some ammonia and methane clouds. The methane clouds absorb red light and reflect blue giving the planet its blue color. Uranus is very cold: 60 K. Its axis of rotation is tipped by 98°! It almost lies in its orbital plane. Thus the planet has extreme season in terms of Sun variability. Approximately 10 very narrow rings were discovered in 1977 when Uranus passed in from of a bright star (the light blinked out many times). The rings are very thin (less than 10 km wide). This is believed to be caused by "Shepard Moons". Spacecraft: Voyager 2 (1986 - just a few days before the Space Shuttle Challenger disaster). It discovered the Shepard Moons around some rings, as predicted. They keep the rings narrow. The atmosphere of Uranus is remarkably featureless. The uneven heating is smoothed out. The moon, Miranda, has quite an amazing surface. It's carved with grooves. Neptune: God of the Sea Planet #8, 8 known moons It is approximately the same size as Uranus (brother planets). It is also mostly composed of Hydrogen and Helium with some methane mixed in for good measure. Neptune was discovered in 1846 (J. Galle), as a result of the analysis of Uranus' orbit: Neptune perturbs Uranus. In 1613 Galileo actually saw it and recorded it in his notebook, but he didn't realize what it was, he just thought it was a star. Spacecraft: Voyager 2 (1989) made an approach within 5000 km of the planet! Discovered complete, but clumpy rings. Atmosphere much more dynamic than Uranus'. Winds up to 1,100 km/hr!. Many white and dark spots (storms). Wispy clouds of methane skirt around. Magnetic field is tilted 50°, and offset from the center (like Uranus'). Triton: is Neptune's largest moon. It has a thin methane atmosphere. Fascinating and varied terrain. Dark plumes - active, icy volcanos! Fault blocks, collapsed basins, craters. The end of Voyager's 12-years Odyssey... Pluto and Charon Planet #9, 1 moon Discovered in 1930 (C. Tombaugh), and its moon, Charon, was not discovered until 1978 (J. Christy) Sometimes Pluto is closer to the Sun than Neptune because of its highly elliptical orbit (e = 0.25). It was closer 1979-1999, it's currently back to being the furthest from the Sun. The orbit is also inclined by 17° with respect to the ecliptic plane. Very large. Despite its being an outer planet, Pluto is completely unlike the jovian worlds. It's actually very similar in composition to Triton (Neptune's largest moon). Charon is has a radius = 0.1R = 0.5R . It's really like a "double planet"! The orbital period is 6 days (tidally locked). Every 250 years there is a 5-year period where Pluto and Charon eclipse eachother as seen from Earth. This allowed astronomers on Earth to determine the physical sizes and densities of the system. The rotation axis is "on it's side" like Uranus. Pluto has a thin, methane atmosphere. Able to keep it because it is so cold there (40 K). 2 thoughts about Pluto: (1) A former moon of Neptune that was stripped away (2) The largest of the Kuiper belt objects .   Asteroids  (click) Often referred to as "minor planets". The majority of these giant rocks occupy a belt between the orbits of Mars and Jupiter (~2 AU) where there could be a planet. The first one discovered was in 1801, named Ceres. Ceres is about 1000 km in diameter and one of the largest asteroids. There are now thousands known and there are estimated to be about 100,000 out there in interplanetary space. There are only about 6 that are larger than 300 km across; most are smaller (< 10 km). Most do not have enough mass to be spherical. 3 types: rocks, iron/nickel, carbon rich Tidal forces exerted by Jupiter likely kept these bodies from being able to form into a planet in the early Solar System.   Comets  Seen in the sky as diffuse, luminous patches, often with long tails. They are basically "dirty snowballs" that evaporate as they approach the Sun. The tail is dust and gas pushed away by the Sun's radiation pressure and solar wind. The tail therefore always points away from the Sun (not always trailing behind the comet!). Comets are like asteroids that are covered with ice. They have typical masses = 10-11 of Earth. They are made of primitive material and provide clues to the early composition of the original "Solar Nebula". Periodic Comets: these comets are bound to the Sun and orbit in very elliptical orbits. They spend most of their existence very far from the Sun and only a short time near it (when the tail develops). Most comets are not periodic. They originate from either the Kuiper Belt or the Oort Cloud: sphere of ~ 1012 comets, ~ 50,000 AU from the Sun. Sometimes the cloud is perturbed by a passing star and sends some comets heading toward the inner Solar System.       Summary Assignment: Chapter 12 Notes on chapter Comets are in the regions known as the ______________ _________ Astroids are concentrated in the _______________ __________ Give facts about each.: Jupiter Saturn Uranus Neptune Pluto and Charon What is a comet? What is an asteroid? When was the first asteroid discovered? _________ Name _____________     Project #3:  Planets  (Make a model and include the Sun, all eight planets and their positions from the sun.  Be creative).   Chapter 13 Meteors and Impacts Meteors: are the name given any piece of space debris that enters the Earth's atmosphere. Meteorites: are debris which actually touch down on the Earth's surface Meteroids: chunks floating through interplanetary space, not in the asteroid belt. Most are small (< 10 m). Most probably come from the asteroid belt; produced by collisions. When they enter Earth's atmosphere (< 100 km), they burn due to friction. They are coming in with very high velocity and hence have much kinetic energy which is converted into heat and light during the burn. Shooting Star When they are found on the surface they can be studied to give clues as to the composition of the early Solar System and its age. Age = 4.6 Billion years Some meteorites seem to come from the Moon, and Mars. Some meteorites have carbon-rich molecules, like amino acids: life precursors. Meteor Showers occur when Earth passes through the debris field that a comet leaves behind after passing through the inner Solar System. Most re-occur each year since the debris field is in orbit around the Sun as well. Some meteors are bigger and when they enter the atmosphere they burn very brightly and leave smoke trails behind. Others are bigger still (~ 0.5 - 50 m) and blow-up upon entering the atmosphere. Then there are even larger objects that collide with Earth: Some groups of Asteroids (mainly "Apollo") have orbits that cross Earth's orbit. Eventually most of them can collide with Earth. Plus there are many comets and random meteroid that cross Earth's orbit and can collide. Examples: Meteor crater in Arizona: 1.2 km diameter, probably the result of a meteorite ~100 m across about 50,000 years ago. Tunguska Event: in 1908, in Siberia what was believed to be a chunk of comet exploded leveling 2000 km2 forest; 15 megatons of TNT. (largest H-bomb ever exploded: 60 megatons). Despite erosion there are > 140 terrestrial craters found. ~ 200 Earth-crossing asteroids known, with typical diameter = 1 km. There are an estimated 2,000 - 4,000 of them out there. We expect a collision to occur once every 300,000 years; 105 - 106 megatons. The smaller blasts (Tunguska) every ~ 300 years. Statistically, averaged over tens of millions of years, you are as likely to die from a cosmic collision as you are from an airplane crash, flood, or tornado. An asteroid with d = 10 km hits the Earth roughly every 30 million years. Such a collision in our time would likely be the end of human civilization. 108 - 109 megaton explosion devastates surrounding area (r = 1000 km); rest of Earth like an oven set to "broil". This is followed by impact "winter" produced by dust in the atmosphere; sunlight is blocked for many years. Hypothesis: The cause of the Cretacious - Tertiary extinction 65 million years ago, when the dinosaurs along with 2/3 of all other life on the planet went extinct, was caused by such a collision. Luis Alvarez (UC Berkeley) 1979 - excellent evidence: thin iridium layer found in rock strata at t = -65 million years. Also the site of an impact crater in the Yucatan peninsula has been dated at about 65 million years old. A Real Threat: in July 1994 comet Shoemaker-Levy 9 collided with Jupiter and all the worlds telescope were there to watch. The comet had been tidally broken up into 20 smaller pieces by a previous encounter with Jupiter. The chunks crashed into Jupiter with energies released of about 6 million megatons each! Formation of the Solar System To understand the observed characteristics of the Solar System we need a Scientific Model that explains how it formed. Many models have been proposed over the last few centuries (as should always be the case). The one that has come to the forefront and is the best so far is called the Nebular Theory. The Nebular Theory has these key features: Begin with a giant cloud (nebula) of gas and dust (enriched with trace amounts of heavy elements, i.e. those heavier than hydrogen and helium). Cloud may span many light-years. Regions of cloud compress due to accoustic waves, shock waves, or some other kind of density waves. Compressed regions begin to collapse under their own gravity. Region become centrally condensed: more matter in center As a region shrinks it becomes hotter due to conservation of energy: gravitational potential energy is converted to kinetic energy. As a region shrinks it begins to spin faster due to conservation of angular momentum: like the ice-skater pulling in her arms. The material begins to flatten into a disk as a natural consequence of collisions. Protoplanetary disks such as those predicted by the theory have been observed in regions of active star formation. At the center of the disk a Protostar is forming. While in the disk colliding dust grains begin sticking together and condensing into larger and larger bodies: Planetesimals. Planetesimals collide, stick together, and begin self-gravitating. Near the protostar temperatures are hot and light elements in gaseous form do not condense out of the disk: small, rocky planets Farther from the protostar planetesimals can collect vast quantities of gases around them and grow larger and large in mass: A fracturing of the disk into smaller disks occurs: larger gaseous planets with many moons. Star blows a strong wind which eventually clears away all small debris and gas that has not condensed out. Terrestrial planets gain atmospheres through volcanic outgasing and comet impacts. Asteroids, Comets, and Meteoroids are left-over debris from the original Nebula Other Planetary Systems If our ideas about how our own Solar System formed are correct then it is reasonable to conclude that many, many other stars would have formed in the same manner and would have planetary systems of their own. Planets around other stars are hard to find. We cannot see their reflected light (too dim and drowned out by star's light). Until recent years this had only been a hypothesis with no data. But now we have very strong evidence that most stars, in fact, have planets around them. Several teams of astronomers across the world have been using a similar technique to find them. One team lead by UC Berkeley's Geoff Marcy has been very successful. They have found these new worlds by their gravitational influence on their parent star. They look for a periodic "wobble" in the motion of the star due to the gravitational tug and motion of the planet around it. The "wobble" is measured as a Doppler Shift in the light from the Star. Can calculate the mass of the planet using Kepler's 3rd law. There are now over 50 Extra-solar planets known. Most have masses similar to Saturn and Jupiter (and greater) and are very close to their parent star. This is likley a selection effect. The Doppler Shift Method is most sensitive to massive planets with short periods and eccentric orbits.   Assignment: Chapter 13 Notes on chapter Define the following: Meteors Meteoroids Shooting star Meteor showers What are the key features of the Nebular Theory? What is used to calculate the mass of a planet? What do we know about the existence of other planets? Chapter 13 Test Chapter 14  BLACK HOLES Questions What is a black hole? Are black holes now considered to be 'proven' real objects in the universe? Where are the best candidates for black holes? How big and hot can black holes get? What happens to matter when it falls into a black hole? If you stuck your hand into a black hole what would happen? How do astronomers study black holes when they can't see them? How do black holes form? Can black holes really suck things up? If the front of a spaceship crosses the horizon of a black hole in a matter of seconds, what does the back of the spaceship see that is still outside? Could a galaxy ever collapse into a black hole? Do black holes ever get full? What is on the other side of a black hole? Can a star clog a black hole that is swallowing it? Will the black hole at the center of the Milky Way eventually eat all the matter in our galaxy? Do black holes die if they are not fed? How does a black hole make room for all the stuff it sucks up? Has the existence of worm holes been demonstrated yet? If you could survive a trip into a black hole, what would you see? What are worm holes? Could black holes really be gateways to other dimensions or universes? How can you use black holes for time travel? What happens when two black holes collide? How do we know that Einstein's equations actually work just inside a black hole's event horizon? What is the importance of black holes to cosmology?     NASA.GOV + Text Only Site + Non-Flash Version + Site Help & Preferences                         RESEARCH www.nineplanets.org Glossary of technical terms and proper names Introduction and FAQ What's New Express Tour Solar System Overview The Sun Mercury Venus Earth The Moon Mars Phobos Deimos Jupiter Metis, Adrastea, Amalthea and Thebe Io Europa Ganymede Callisto Leda, Himalia, Lysithea, Elara, Ananke, Carme, Pasiphae and Sinope Recently discovered moons Saturn Pan and Atlas Prometheus and Pandora Epimetheus Janus Mimas Enceladus Tethys, Telesto and Calypso Dione and Helene Rhea Titan Hyperion Iapetus Phoebe Recently discovered satellites Uranus Cordelia, Ophelia, Bianca, Cressida, Desdemona, Juliet, Portia, Rosalind, Belinda and Puck Miranda Ariel Umbriel Titania Oberon Caliban, Sycorax, Prospero, Setebos, Stephano, and Trinculo Neptune Naiad, Thalassa, Despina and Galatea Larissa Proteus Triton Nereid Pluto Charon Nix and Hydra Small Bodies Comets Comet Halley Comet Shoemaker-Levy 9 The Kuiper Belt and the Oort Cloud Sedna Asteroids 951 Gaspra 243 Ida 253 Mathilde 433 Eros Meteors, Meteorites and Impacts The Interplanetary Medium Other Solar Systems Seeing the Solar System with your own eyes (or binoculars or a small telescope) Spacecraft involved in planetary science How you can help support the continued exploration of space   Appendices Solar System Data: Orbital, Physical, Misc Extrema, the biggest, brightest, etc. Discovery Chronology The Origin of the Solar System Planetary Linguistics, including the planets' names in various languages Astronomical Names and how they're assigned Hypothetical Planets (Planet X et al, or "Don't believe everything you read") Planetary Picture List: images on the Net; posters, calendars and prints offline Planetary Music: classical music relating to the planets Astronomical People (with images) People from the University of Michigan's wonderful "Windows to the Universe", ·         Spaceflight Glossary of Spaceflight Terminology from JPL NASA Thesaurus NASA NGST Glossary Dictionary Of Technical Terms For Aerospace Use from NASA LeRC ·         Mythology Encyclopedia Mythica, an encyclopedia of mythology and more Bulfinch's Mythology