Chapter 1 Astronomy Lecture PDF

Chapter 1 What are We? How Do We Know? Guidepost As you study astronomy, you will learn about yourself. You are a planet walker, and you should understand what it means to live on a planet that whirls around a star drifting through a universe of stars and galaxies. You owe it to yourself to know...

Chapter 1 What are We? How Do We Know? Guidepost As you study astronomy, you will learn about yourself. You are a planet walker, and you should understand what it means to live on a planet that whirls around a star drifting through a universe of stars and galaxies. You owe it to yourself to know where you are. That is the first step to knowing what you are. In this chapter, you will meet four essential questions about astronomy: Why should we study astronomy? How do scientists know about nature? Where are you in the universe? How does human history fit on the time scale of the universe? Guidepost (continued) Besides learning about astronomy, you will consider important questions about science: How do we know? How does science work? How do we know? What is the difference between a scientific argument and an advertisement? In this chapter, a cosmic zoom takes you roaring outward through the universe checking out its major features. In the next chapter, you will return to Earth and begin your study by looking at the stars in the night sky. Scales of Size and Time Astronomy deals with objects on a vast range of size scales and time scales. Most of these size and time scales are way beyond our every-day experience. Humans, the Earth, and even the solar system are tiny and unimportant on cosmic scales. A Campus Scene 16 x 16 m  Let us zoom out by a factor of 100, Let us travel throughout the Universe A City View 1.6 km x 1.6 km  The Landscape of Pennsylvania How much time does it take to cross this distance? Car (100 km/hr)  1.6 hr Plane (900km/hr) 10 min Rocket (10,000km/hr)  1 min Light (300,000 km/s)  0.0005 s 160 km x 160 km The Earth Car (100 km/hr)  5.3 days Plane (900km/hr) 14 hrs Rocket (10,000km/hr)  1.3 hrs Light (300,000 km/s)  0.043 s Diameter of the Earth: 12,756 km Earth and Moon Car (100 km/hr)  160 days Plane (900km/hr) 18 days Rocket (10,000km/hr)  1.6 days Light (300,000 km/s) 1.3 sec Distance Earth – Moon: 384,000 km Earth Orbiting Around the Sun Car (100 km/hr)  171 yrs Plane (900km/hr) 19 yrs Rocket (10,000km/hr)  1.7 yrs Light (300,000 km/s) 8.3 min Distance Sun – Earth = 150,000,000 km Earth Orbiting Around the Sun (2) In order to avoid large numbers beyond our imagination, we introduce new units: 1 Astronomical Unit (AU) = Distance Sun – Earth = 150 million km Mercury Venus The Solar System Car (100 km/hr) - --------- Plane (900km/hr) - --------- Rocket (10,000km/hr)  171 yrs Light (300,000 km/s) 14 hrs Approx. 100 AU Curiosity on Mars  Latest Pluto’s Flyby New Horizons July 2015  Pluto Mars Sun Earth Neptune Venus Mercury Uranus Saturn Jupiter The Motion of the Planets The planets are orbiting the sun almost exactly in the plane of the Ecliptic. te r J up i s Venus Ma r Ear th Mercury Satur n The Moon is orbiting Earth in almost the same plane (Ecliptic). (Almost) Empty Space Around Our Solar System Car (100 km/hr) - ------ Plane (900km/hr) - ----- Rocket (10,000km/hr) - ---- Light (300,000 km/s) 60 days Approx. 10,000 AU The Solar Neighborhood Approx. 17 light years The Solar Neighborhood (2) New distance scale: 1 light year (ly) = Distance traveled by light in 1 year = speed of light x one year = 300,000 km/s x 365.25 x 24 x 60 x 60 s = 9.5 x 1012 km = 1013 km = 10,000,000,000,000 km Approx. 17 light years (= 1 + 13 zeros) Nearest star to the Sun: = 10 trillion km Proxima Centauri, at a = 1016 m distance of 4.2 light years =  63,000 AU  (90 kmph) (60,000 kmph) The Extended Solar Neighborhood 300,000 km/s – 1700 yrs Approx. 1,700 light years The Milky Way Galaxy 300,000 km/s – 100,000 yrs Diameter of the Milky Way: ~ 100,000 ly Sombrero Galaxy (M101) How are galaxies classified? (More in Chapter 10) The Local Group: Our Cluster of Galaxies Distance to the nearest large galaxies: several million light years The Universe on Very Large Scales Clusters of galaxies are grouped into superclusters. Superclusters form filaments and walls around voids.  Video Trailer 3: Scale of the Universe How Do We Know? The Scientific Method Observed facts - phenomenology Possible explanation – hypothesis / theory Testable predictions: What else should we see if the hypothesis / theory is true? Further observations to test predictions Observations contradict Observations confirm predictions predictions Support for Modify or reject hypothesis/theory – hypothesis Develop further predictions  Powers of ten 100 = 1 101 = 10 102 = 10 x 10 = 100 103 = 10 x 10 x 10 = 1000 104 = 10 x 10 x 10 x 10 = 10,000 105 = 10 x 10 x 10 x 10 x 10 = 100,000 106 = 10 x 10 x 10 x 10 x 10 x 10 = 1000,000 (million) 109 = 1000,000,000 (billion) 1012 = 1000,000,000,000 (trillion) 10-1 = 1/10 = 0.1 10-2 = 1/100 = 0.01 10-3 = 1/1000 = 0.001 (millimeter) 10-6 = 1/1000,000 = 0.000001 (micrometer) 10-9 = 1/1000,000,000 = 0.000000001 (nanometer)  Some Common Misconceptions Light-year is a unit of time… Stars look like disks when seen through a telescope… People often say “galaxy” when they mean “solar system’, and they sometimes confuse both terms with “universe.”