Copyright © 2009 Pearson Education, Inc. Chapter 3 The Science of AstronomyCopyright © 2009 Pearson Education, Inc. Internet Anything you write or post assume can be read on internet. Be careful! The American Astronomical Society finds itself at an important tipping point. Funding in Washington DC is declining and yet we are training more and more astronomers. As your Vice President, I will bring Bold & Fresh ideas to help the membership deal with these substantial issues. As my new Bold & Fresh approach, I would work to bring back Disembowelment and Human Sacrifice to astronomy, as was once practiced by the great astronomers. At one time, we had the ears of kings and Gods as we guarded the astronomical secrets from the unwashed. We had the funding agencies and GS workers build palaces and temples to our knowledge and we got to wear cool hats and stuff with red feathers. We have lost this momentum, and I will work to bring back our former glory. It is important to insure that historically underrepresented groups such as women, solar astronomers, and string theorists would be encouraged to participate. By narrowing the human sacrifices to astronomers that by consensus could easily be decapitated, we would also reduce the total number of members as we regain the prestige and funding we so obviously deserve. I have no doubt that the society at large could easily nominate astronomers for this important service to our profession, starting perhaps with department chairmen, thesis advisors, Deans, or the guy that wrote IRAF.Copyright © 2009 Pearson Education, Inc.Copyright © 2009 Pearson Education, Inc. Tycho’s star was the real “revolution” Tycho showed that the new star which appeared for a few months had no parallax, and thus was farther away than the Moon, in contradiction to Aristotle and the Church. Aristotle was wrong and the Church was not infallable.Copyright © 2009 Pearson Education, Inc. Kepler’s Three Laws • Planets revolve on elliptical orbits • Planets sweep out equal areas in equal times • Semi-major axis cubed equals period squared P2 = a3Copyright © 2009 Pearson Education, Inc. Question: if the period is 16 years, what is the semi-major axis? • A. 64 years • B. 4 light years • C. 36 years • D. 32 years trick question! (16)2 = a3, or a3=256 a=6.35AU. Understand how to do this formula!Copyright © 2009 Pearson Education, Inc. How did Galileo solidify the Copernican revolution? Galileo (1564–1642) overcame major objections to the Copernican view. Three key objections rooted in the Aristotelian view were the following: 1. Earth could not be moving because objects in air would be left behind. 2. Noncircular orbits are not “perfect” as heavens should be. 3. If Earth were really orbiting Sun, we’d detect stellar parallax.Copyright © 2009 Pearson Education, Inc. Galileo’s experiments showed that objects in air would stay with a moving Earth. Overcoming the first objection (nature of motion): • Aristotle thought that all objects naturally come to rest. • Galileo showed that objects will stay in motion unless a force acts to slow them down (Newton’s first law of motion). nbs’s opinion – both were right, they just had different theoriesCopyright © 2009 Pearson Education, Inc. Overcoming the second objection (heavenly perfection): • Tycho’s observations of comet and supernova already challenged this idea. • Using his telescope, Galileo saw: — Sunspots on the Sun (“imperfections”) — Mountains and valleys on the Moon (proving it is not a perfect sphere) — nbs’s opinion. I have never understood how anyone could think the Moon was “perfect.” To my eye, it clearly has splotches.Copyright © 2009 Pearson Education, Inc. • Tycho thought he had measured stellar distances, so lack of parallax seemed to rule out an orbiting Earth. Tycho miscalculated the effects of refraction from the Earth’s atmosphere, among other small errors. • Galileo showed stars must be much farther than Tycho thought—in part by using his telescope to see that the Milky Way is countless individual stars. • If stars were much farther away, then lack of detectable parallax was no longer so troubling. • nbs’s opinion: this is all well and good, but it is a difficult theory to find other predictions, if the stars are indeed very far away. Overcoming the third objection (parallax):Copyright © 2009 Pearson Education, Inc. Galileo also saw four moons orbiting Jupiter, proving that not all objects orbit Earth. This was the killer argument. This was just like the Solar System, with a similar law to Kepler’s 3rd Law.Copyright © 2009 Pearson Education, Inc. Galileo’s observations of phases of Venus proved that it orbits the Sun and not Earth. The recent Kepler results have seen this in a planet around another star. There they see a small increase in brightness before the planet goes behind the star – which would not happen in a geocentric theory. It also means that with really good measuremnets we should be able toCopyright © 2009 Pearson Education, Inc. Galileo Galilei In 1633 the Catholic Church ordered Galileo to recant his claim that Earth orbits the Sun. His book on the subject was removed from the Church’s index of banned books in 1824. Galileo was formally vindicated by the Church in 1992.Copyright © 2009 Pearson Education, Inc. What have we learned? • How did Copernicus, Tycho, and Kepler challenge the Earth-centered idea? — Copernicus created a Sun-centered model; Tycho provided the data needed to improve this model; Kepler found a model that fit Tycho’s data. • What are Kepler’s three laws of planetary motion? 1. The orbit of each planet is an ellipse with the Sun at one focus. 2. As a planet moves around its orbit it sweeps out equal areas in equal times. 3. More distant planets orbit the Sun at slower average speeds: p2 = a3.Copyright © 2009 Pearson Education, Inc. What have we learned? • How did Galileo solidify the Copernican revolution? — His experiments and observations overcame the remaining objections to the Sun-centered solar system.Copyright © 2009 Pearson Education, Inc. 3.4 The Nature of Science • How can we distinguish science from nonscience? • What is a scientific theory? Our goals for learning:Copyright © 2009 Pearson Education, Inc. How can we distinguish science from nonscience?
View Full Document
Unlocking...