Ast 111.. chapter 2
Ast 111.. chapter 2 AST 111
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This 104 page Class Notes was uploaded by Rupak Kadel on Tuesday September 20, 2016. The Class Notes belongs to AST 111 at University of Southern Mississippi taught by Christopher Sirola in Fall 2016. Since its upload, it has received 4 views.
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Date Created: 09/20/16
Notes for Astronomy: Part 2 Dr. Christopher Sirola Department of Physics & Astronomy University of Southern Activity: Astronomy vs. Astrology The Sun passes in front of many constellations (the “zodiac”) during a year. Most are animals, thus the “zoo” in “zodiac”. Astrology Activity Astrology is the notion that one’s future and personality are determined by where the Sun is at the moment of Astrology Activity Look below to find your astrological sign: Aquarius: 1/20 – Leo: 7/23 – 8/22 2/18 Pisces: 2/19 Virgo: 8/23 – 9/22 – 3/20 Aries: 3/21 Scorpio: 10/23 –/22 – 4/19 aurus: 11/22 4/20 – 5/20 Sagittarius: 11/22 – Gemini: 5/21 – 12/21 Capricorn: 6/20 Cancer: 12/22 – 1/19 6/21 – 7/22 Astrology Take the astrology • Answer as honestly as ppossiblety quiz! • There are no “right” or “wrong” answers • Each sign has a different quiz • Tally your “yes” answers when finished • What is our threshold for success? • We will do a class comparison Astrology Activity While you wait - what the signs mean: Aquarius: Water Leo: Lion Bearer Pisces: Pair Virgo: oung of fish Aries: Ram maiden Libra: Taurus: Bull Scorpioncorpio: Gemini: Twin Sagittarius: boys Cancer: Archer/Satyr Crab Capricorn: Goat/Fish/Satyr Astrology ActiThey Results: • What was our threshold? • Did you personally meet the threshold? • Did the class meet the threshold? Astrology After sharing results with neighbors: • What can you say about the quizzes? • Why did you get the answers you did? • Has this changed your opinion? Astrology Activity It has been claimed that one’s sign determines one’s athletic abili.y Let’s examine a sample of highly successful athletes. Astrology Below is a histogram of 120 athletes’ astrological signs. e Astrological Signs for Athletes l t f 15 14 14 r 12 12 b 10 11 m 10 9 8 8 9 N 7 6 5 0 Astrology Activity The average athleteper is 10 Are any s far sign. signs very from averag t Astrological Signs for Athletes h e? 15 14 14 e 12 12 11 m 10 9 9 10 u 8 8 7 N 6 5 0 Astrology What do youActivity does a think – sign person’s determint thAstrological Signs for Athletesic l ability? 15 14 14 e 12 12 11 m 10 9 9 10 N 8 8 7 6 5 0 Science vs. Pseudoscience • Offers a model (tScience: • Uses observations & experiments • Its predictions are falsifiable (Selected) History of Astronomy For most of history, people thought the Earth sat at the center of the universe. Geocentric System Note the 7 “planets”, surrounded by a sphere of fixed stars. The “Prime Mover” set it all in motion. Geocentric System The most famous advocate of this “geocentric” system was Aristotle (lived 4 century BCE) of ancient Greece. Geocentric Aristotle’s view was that planets orbited the Earth in circles at constant speed. calleds “uniform circular motion”. Geocentric System Aristotle’s other views of • Objects rise or sink according to what they are made of (“element”) • Objects in the sky are “perfect” • Only what can be seen matters • Laws of nature are different for Geocentric System Howev er, every so often, 5 of the planet s revers Geocentric System For example, here is Mars in 2003. This behavior is called “retrograd e motion.” Geocentric System The Sun & Moon don’t show this, but the other planets do. Geocentric System This issue lay unresolved until Claudius Ptolemy tackled it c. 150 CE. Ptolemy (we think) was a Greek living in Alexandria, Geocentric Ptolemytem suggested planets orbit Earth on an off -set wheel (“epicycle”). This allowed him to keep Aristotle’s uniform circular Geocentric System This sim shows how a planet can trace out retrograde motion in the geocentric system. Geocentric System Ptolemy’s model was the standard for 1300 years. Heliocentric But Ptolemy’s model wasn’t the About the same time Aristotle was at work, Aristarchus of Samos (also Greece) suggested a different Heliocentric System Aristarchus noted that the Moon & Sun subtend the same angle on the sky. Heliocentric System From lunar eclipses, he estimated the Sun to be 20 times further from the Earth than the Moon. Heliocentric If the Sun looks the same size as the Moon, but is really 20 times further away, it must be 20 times larger across. (The true ratio is 400, but the basic idea is correct) Heliocentric System In Aristarchus’ “heliocentri c” system, the Earth is just another planet orbiting the Sun. Heliocentric Most Systeat the time people thought this his was silly, model was so ignored. Can you think of a reason why? Heliocentric System In 1453, Nicholas Copernicus of Poland published an updated version of the heliocentric system. Heliocentric Thestem heliocentric system dramatically simplifies the explanation for retrograde Heliocentric System The Earth now orbits the Sun as a planet. Note the Moon still orbits the Earth. Heliocentric System So retrograde motion is an apparent effect that shows up when one planet passes Heliocentric System It doesn’t matter which planet moves faster; the effect shows up in both Heliocentric Copernicus’ version did have a problem, though. He kept Aristotle ’s uniform circular motion. Heliocentric System With the observations available, nobody in Copernicus’ day could tell definitively which version was better. Laws of Planetary Motion In the last decades of the 16 century, the Danish nobleman T ycho Brahe created the first modern research institute. Laws of Planetary MotionTycho made the best astronomical instruments before the advent of the telescope. Tycho was able to measure positions of planets to within 2 arcminutes of precision. Laws of Planetary Motion For comparison, the Full Moon is 30 arcminutes across. precision This is about as good as anyone can do without a telescope. Laws of Planetary When Tycho died in 1603, Johannes Kepler took over his data. With them, Kepler discovered how planets really 1 Law of Planetary Motion (1609Planets do not orbit the Sun in Aristotelian circles; rather, the shape of an orbit is an ellipse. 1 Law of Planetary Furthermore, the Sun is not at the center of the ellipse, but off to the side (at one focus of the ellipse). 2nd Law of Planetary Motion (1609) Second, the closer a planet is to the Sun, the faster it moves. 2nd Law of Planetary Motion More specifically, planets sweep out equal areas in equal times. 3 Law of Planetary Motion (1619) rd The 3 law relates the distances of the planets from the Sun to their orbital periods. 3 Law of Planetary Motion where P is the period measured in years and a is the average distance to the Sun in AU (“Astronomical 3 Law of Planetary Motion Example: Suppose a new planet is discovered 4 AU from the Sun. What is its period? 3 Law of Planetary Motion Astronomical Telescopes: Part #1 The person credited with the invention of the telescope was a Dutch eyeglass maker named Hans Lippershey. Telescopes: Part #1 This was in 1608. By 1609, word had reached an Italian scientist named Galileo Galileo quickly built his own telescope. Telescopes: Galileo was the first to train a telescope at the sky. From 1609- 1610, he made One of Galileo’s 5 separate original discoveries. telescopes. Telescopes: Part #1 Though Galileo and Kepler never met, their work began the scientific A reproduction ofrevolution. antelescope.lean Galileo’s Discoveries Prior to Galileo, nobody knew what to make of the Milky Way. Photo taken via ISO 400 camera on Sept. 5 2013 Galileo’s Galileo showedes the Milky Way was simply a collection of faint stars. This implies there are objects we can’t see. Galileo’s Discoveries Before Galileo, people generally assumed the Sun was “perfect” (i.e. no blemishes or features). Galileo’s Discoveries Galileo described sunspots in detail and used them to show the Sun rotates on its aThis implies objects in space are not Galileo’s Before Galileo,ries people assumed different laws applied to the heavens compared to the Galileo’s Discoveries Galileo measured features (craters, mountains etc.) on the Moon.bjec This ts in space are implies to laws subject nature Galileo’s With Copernicuss (still before Galileo), the debate was whether objects orbited the Earth or the Sun exclusively. Galileo’s Discoveries Galileo found four moons (satellites) orbiting Jupiter. This implies objects can orbit other objects besides Galileo’s Discoveries Here is a page of Galileo’s notes showing moons orbiting Jupiter. Galileo’s Before Galileo (iferies people thought about it), if Earth was at the center, then Venus would show a complete set Galileo’s Discoveries In the heliocentric system, we cannot see a “Full” Venus from Earth. Galileo’s observations failed to show a “Full” Venus; thus the Earth Celestial Mechanics A few decades after Galileo & Kepler, Isaac Newton put math & science together to explain how the solar system works. Celestial Mechanics Pertinent to our current studies are Newton’s Laws of Motion & his Universal Law of Gravity. Law of Motion #1 An object at rest tends to stay at rest; an object in motion tends to stay in motion. Law of Motion #2 Law of Motion #3 When an object exerts a force, it feels an equal & opposite force. Law of Gravitation Law of Gravitation For the Earth & Moon example, pull together via each gravity. Why don’t they collide? Celestial Mechanics The Moon’s motion is a combination of its tendency to keep moving in a straight line (Law #1) and the force it feels from the Earth (Laws #2 & #3). Celestial Mechanics Newton showed that Kepler’s Laws oare consequenceson of his own Laws of Motion & Law of Gravity. Celestial Mechanics Further, Newton’s Laws show that Kepler’s Laws are themselves approximations. Celestial Mechanics For example, the Earth & Moon pull on each other with the same amount of gravitational force. Celestial Mechanics This means that, rather than the Moon orbiting the Earth, both objects orbit a common “Center of Mass”. Celestial Mechanics Astronomers even use this idea to find planets orbiting other stars when the planets are otherwise invisible. Celestial Mechanics Watch as this “orbits” star a Centerabout it of Mass shares with an planet: unseen Celestial Mechanics Celestial Mechanics Celestial Mechanics Celestial Mechanics Celestial Mechanics Celestial Mechanics Celestial Mechanics Celestial Mechanics Celestial Mechanics Celestial Mechanics Celestial Mechanics By observing the “wobble” of a star, astronomers can estimate the mass & orbital characteristics of its planet. Celestial This Mechanics is a plot of a star’s wobble due to an unseen planet. Celestial Mechanics Applications of Astronomy contemporary His(and friend) of Newton’s was Edmond Halley. It was he who arranged to have Newton’s work Application of History #1 Halley is most famous for the comet that bears his name… but why? Halley’s Comet during approach in 1986. Application of In 1705, using History #1 Newton’s laws and historical records, Halley Plaque honoring correctly Halley in predicted Westminster Abbey.a comet’s return in Application of History #1 This showed that (a) Comets are part of the solar system Orbit of Halley’s(b) Newton’s Comet. The Laws are lthe orbitofle is universal. Uranus. Application of History #2 In ancient Greece, Hipparchus mapped the positions of stars on the Detail from Raphael’s The sky to make School of Athensone of the first Celestial Application of History #2 Comparing this & other historical records, Halley argued that stars actually move independently. Application of History #2 Thus Halley showed that space is really 3- dimensional and the Celestial Sphere is an The next planet In the late 1700s, William Herschel emigrated from Hanover (Germany) to England. The next Herschel and his sister planet Caroline were the best lens- grinders in the world. Their telescopes were therefore The next Herschel saw a blue disk that moved slowly but steadily compared to the star background. He concluded the disk must be a new planet. The next Herschel wanted to name the new planet “George”, after his patron, George III. Instead, it was sensibly named Uranus. The next We willanet discuss further solar system discoveries as they arise.
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