Our Place in Universe

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Published on November 3, 2008

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Chapter 1,2 Our Place in the Universe, Night sky : Chapter 1,2 Our Place in the Universe, Night sky To understand the universe, astronomers use the laws of physics and construct testable theories and models. : To understand the universe, astronomers use the laws of physics and construct testable theories and models. Scientific method Based on observation, logic, and skepticism. Hypothesis A collection of well thought-out ideas to explain a phenomena Model. Hypotheses that have withstood observational and experimental tests. Theory A well-founded body of related hypotheses and models that form a self-consistent description of nature. Science, religion, and pseudo-science : Science, religion, and pseudo-science Scientific theories are experimentally verifiable (or falsifiable) and predictive. They address how questions (e.g. How do stars form? When will the next lunar eclipse be?) Religious and ethical statements are (generally) not verifiable. They address why questions (e.g. Why does the Universe exist? What kind of life is worth living?). These are not intrinsically less worthwhile than scientific inquiries, they are simply addressing different questions. Pseudo-science theories pretend to be scientific but are either not falsifiable (e.g. seances, intelligent design) or supporters or use anecdotal evidence to support claims (e.g. astrology, magnetic ‘healing’, ). Scepticism and Truth : Scepticism and Truth Role of scepticism. An essential part of the scientific method. Scientists always question the basis for an scientific assertion. This is often considered ‘impolite’ behavior in social settings, but is not impolite in scientific discussion. ‘What is truth?’ - Scientific theories are not statements of truth. They are the best explanation for observed facts, but are subject to revision or falsification. Example: Gravitation (Newton vs. Einstein). Which are valid scientific hypotheses? : Which are valid scientific hypotheses? Pluto is made of green cheese. The soul lives on after the body dies. Jon Stewart is the funniest person alive. Osama Bin Laden is dead. All asteroids contain fossil material. God made all things. Astronomers use angles to denote the positions and apparent sizes of objects in the sky. : Astronomers use angles to denote the positions and apparent sizes of objects in the sky. Angular Measure : Angular Measure Basic unit of angular measure is the degree º Full circle measures 360º Right angle measures 90º Angular distance is the number of degrees across the sky between two points. Angular diameter or angular size is the number of degrees from one side of an object to the other side. The angular sizes of the Moon and the Sun are both 0.5º Try this: Estimate approximate angular size of this disk? (use your hand) : Try this: Estimate approximate angular size of this disk? (use your hand) Angular Measure for Small Angles : Angular Measure for Small Angles 1º = 60 arcminutes = 60′ 1′ = 60 arcseconds = 60″ e.g., On January 1, the planet Saturn had an angular diameter of 19.7″ as viewed from Earth. Moon: Angular sizes : Moon: Angular sizes Sea of Tranquility (Apollo 11 site) Example: On November 28, 2000, the planet Jupiter was 609 million kilometers from Earth and had an angular diameter of 48.6″. Using the small-angle formula, determine Jupiter’s actual diameter. : Example: On November 28, 2000, the planet Jupiter was 609 million kilometers from Earth and had an angular diameter of 48.6″. Using the small-angle formula, determine Jupiter’s actual diameter. D = 48.6″ x 609,000,000 km / 206206 = 143,000 km Powers-of-ten notation is a useful shorthand system of writing really large numbers. : Powers-of-ten notation is a useful shorthand system of writing really large numbers. 100 = 1 101 = 10 102 = 100 103 = 1,000 104 = 10,000 106 = 1,000,000 109 = 1,000,000,000 One Ten (deca-) Hundred (centa-) Thousand (kilo-) Ten thousand Million (mega-) Billion (giga-) Powers-of-ten notation is a useful shorthand system of writing really small numbers. : Powers-of-ten notation is a useful shorthand system of writing really small numbers. 100 = 1 10-1 = 0.10 10-2 = 0.01 10-3 = 0.001 10-4 = 0.0001 10-6 = 0.000001 10-9 = 0.000000001 One One-tenth (deci-) One-hundredth (centi-) One-thousandth (milli-) One-ten-thousandth One-millionth (micro-) One-billionth (nano-) Scientific Notation example: Population of Earth : Scientific Notation example: Population of Earth 6.5 billion = 6.5∙109 (6,500,000,000) Astronomical distances : Astronomical distances Astronomical Unit (AU): One AU is the average distance between Earth and the Sun (150 million km or 93 million miles). Light Year (ly): One light year (ly) is the distance light can travel in one year at a speed of about 3 x 105 km/s or 186,000 miles/s (9.46 X 1012 km or 63,240 AU). Parsec (pc): One parsec (pc) is the distance from which Earth would appear to be one arcsecond from the Sun. One parsec = 3.27 light years. 1.2 The Scale of the Universe : 1.2 The Scale of the Universe How big is Earth compared to our solar system? How far away are the stars? How big is the Milky Way Galaxy? How big is the universe? How do our lifetimes compare to the age of the universe? Guiding questions: How big is Earth compared to our solar system?Let’s reduce the size of the solar system by a factor of 10 billion; the Sun is now the size of a large grapefruit (14 cm diameter).How big is Earth on this scale? : How big is Earth compared to our solar system?Let’s reduce the size of the solar system by a factor of 10 billion; the Sun is now the size of a large grapefruit (14 cm diameter).How big is Earth on this scale? an atom a ball point a marble a golf ball Let’s reduce the size of the solar system by a factor of 10 billion; the Sun is now the size of a large grapefruit (14 cm diameter).How big is Earth on this scale? : Let’s reduce the size of the solar system by a factor of 10 billion; the Sun is now the size of a large grapefruit (14 cm diameter).How big is Earth on this scale? an atom a ball point a marble a golf ball The scale of the solar system : The scale of the solar system On a 1-to-10 billion scale: Sun is the size of a large grapefruit (14 cm) Earth is the size of a ball point, 15 meters away. How far away are the stars?On our 1-to-10 billion scale, it’s just a few minutes walk to Pluto.How far would you have to walk to reach Alpha Centauri? : How far away are the stars?On our 1-to-10 billion scale, it’s just a few minutes walk to Pluto.How far would you have to walk to reach Alpha Centauri? 1 mile 10 miles 100 miles the distance across the U.S. (2500 miles) Answer: D, the distance across the U.S. : Answer: D, the distance across the U.S. How big is the Milky Way Galaxy? : How big is the Milky Way Galaxy? The Milky Way has about 100 billion stars. On the same ten billion-to-one scale…. Thought QuestionSuppose you tried to count the more than 100 billion stars in our galaxy, at a rate of one per second… How long would it take you? : Thought QuestionSuppose you tried to count the more than 100 billion stars in our galaxy, at a rate of one per second… How long would it take you? a few weeks a few months a few years a few thousand years Suppose you tried to count the more than 100 billion stars in our galaxy, at a rate of one per second… How long would it take you? : Suppose you tried to count the more than 100 billion stars in our galaxy, at a rate of one per second… How long would it take you? a few weeks a few months a few years a few thousand years How big is the Universe? : How big is the Universe? The Milky Way is one of about 100 billion galaxies. 1011 stars/galaxy x 1011 galaxies = 1022 stars As many stars as grains of (dry) sand on all Earth’s beaches… Slide 31: Now let’s step through the Universe in powers of 10: How do our lifetimes compare to the age of the Universe? : How do our lifetimes compare to the age of the Universe? The Cosmic Calendar: a scale on which we compress the history of the universe into 1 year. How do our lifetimes compare to the age of the Universe? : How do our lifetimes compare to the age of the Universe? The Cosmic Calendar: a scale on which we compress the history of the universe into 1 year. Review : Review How big is Earth compared to our solar system? The distances between planets are huge compared to their sizes—on a scale of 1-to-10 billion, Earth is the size of a ball point and the Sun is 15 meters away How far away are the stars? On the same scale, the stars are thousands of km away How big is the Milky Way galaxy? It would take more than 3,000 years to count the stars in the Milky Way Galaxy at a rate of one per second, and they are spread across 100,000 light-years Slide 35: How big is the universe? The observable universe is 14 billion light-years in radius and contains over 100 billion galaxies with a total number of stars comparable to the number of grains of sand on all of Earth’s beaches How do our lifetimes compare to the age of the universe? On a cosmic calendar that compresses the history of the Universe into one year, human civilization is just a few seconds old, and a human lifetime is a fraction of a second 1.3 Spaceship Earth : 1.3 Spaceship Earth How is Earth moving in our solar system? How is our solar system moving in the Galaxy? How do galaxies move within the Universe? Are we ever sitting still? Key questions: How is Earth moving in our solar system? : How is Earth moving in our solar system? Contrary to our perception, we are not “sitting still.” We are moving with the Earth in several ways, and at surprisingly fast speeds… The Earth rotates around its axis once every day. Earth orbits the Sun (revolves) once every year: : Earth orbits the Sun (revolves) once every year: at an average distance of 1 AU ≈ 150 million km. with Earth’s axis tilted by 23.5º (pointing to Polaris) and rotating in the same direction it orbits, counter-clockwise as viewed from above the North Pole. Our Sun moves randomly relative to the other stars in the local Solar neighborhood… : Our Sun moves randomly relative to the other stars in the local Solar neighborhood… typical relative speeds of more than 70,000 km/hr but stars are so far away that we cannot easily notice their motion … And orbits the galaxy every 230 million years. More detailed study of the Milky Way’s rotation reveals one of the greatest mysteries in astronomy: : More detailed study of the Milky Way’s rotation reveals one of the greatest mysteries in astronomy: Most of Milky Way’s light comes from disk and bulge … …. but most of the mass is in its halo How do galaxies move within the universe? : How do galaxies move within the universe? Galaxies are carried along with the expansion of the Universe. But how did Hubble figure out that the universe is expanding? Hubble discovered that: : Hubble discovered that: All galaxies outside our Local Group are moving away from us. The more distant the galaxy, the faster it is racing away. Conclusion: We live in an expanding universe. Are we ever sitting still? : Are we ever sitting still? Earth rotates on axis: > 1,000 km/hr Earth orbits Sun: > 100,000 km/hr Solar system moves among stars: ~ 70,000 km/hr Milky Way rotates: ~ 800,000 km/hr Milky Way moves in Local Group Universe expands Review : Review How is Earth moving in our solar system? It rotates on its axis once a day and orbit the Sun at a distance of 1 A.U. = 150 million km How is our solar system moving in the Milky Way galaxy? Stars in the Local Neighborhood move randomly relative to one another and orbit the center of the Milky Way in about 230 million years Slide 45: How do galaxies move within the universe? All galaxies beyond the Local Group are moving away from us with expansion of the Universe: the more distant they are, the faster they’re moving Are we ever sitting still? No! 1.4 The Human Adventure of Astronomy : 1.4 The Human Adventure of Astronomy How has the study of astronomy affected human history? Key question: How has the study of astronomy affected human history? : How has the study of astronomy affected human history? Copernican Revolution showed that Earth was not the center of the universe (Chapter 3) Study of planetary motion led to Newton’s Laws of motion and gravity (Chapter 4) Newton’s laws laid the foundation of the industrial revolution Modern discoveries are continuing to expand our “cosmic perspective” Review : Review How has the study of astronomy affected human history? Throughout history, astronomy has provided an expanded perspective on Earth that has grown hand in hand with social and technological developments

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