Ch. 2 Discovering the Universe for Yourself

Transcription

1 Ch. 2 Discovering the Universe for Yourself 1

2 2.1 Patterns in the Night Sky Our goals for learning: What does the universe look like from Earth? Why do stars rise and set? 2

3 What does the universe look like from Earth? With the naked eye, we can see more than 2,000 stars as well as the Milky Way. 3

4 A constellation is a region of the sky. Constellations 88 constellations fill the entire sky. 4

5 Often you see this type of diagram... 5

6 Consider the dome of the sky over our heads. mixing bowl 6

7 Consider the dome of the sky over our heads. The Celestial Sphere!! inverted mixing bowl. 7

8 Quiz The brightest stars in a constellation A. All belong to the same star cluster. B. All lie at about the same distance from Earth. C. May actually be quite far away from each other. 8

9 The Celestial Sphere Stars at different distances all appear to lie on the celestial sphere. Ecliptic is Sun s apparent path through the celestial sphere. 9

10 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, counterclockwise as viewed from above the North Pole. 10

11 The Celestial Sphere The 88 official constellations cover the celestial sphere. Imagining a spinning Celestial Sphere surrounding Earth aids in thinking about the position and motion of the sky 11

12 The Milky Way A band of light making a circle around the celestial sphere. What is it? Our view into the plane of our galaxy. 12

13 The Milky Way 13

14 Location: Texas Exposure: 60 min 28 mm lens Credit: Richard Bell

15 The Local Sky An object s altitude (above horizon) and direction (along horizon) specifies its location in your local sky 15

16 The Local Sky Zenith: The point directly overhead Horizon: All points 90 away from zenith Meridian: Line passing through zenith and connecting N and S points on horizon 16

17 Here s the Celestial Sphere... Celestial Sphere Rotation Star B 2 Star A 1 2 Celestial Sphere 3 Celestial Sphere Horizon 4 Celestial Sphere Rotation Figure 2 17

18 Is the horizon shown a real physical horizon, or an imaginary plane that extends from the observer and Earth out to the stars? Celestial Sphere Rotation 1 Star B 2 Star A 2 Can the observer shown see an object located below the horizon? Celestial Sphere Celestial Sphere Is there a star that is in an unobservable position? 4 3 Horizon When a star travels from being below the observer s horizon to being above the observer s horizon, is that star rising or setting? Figure 2 Celestial Sphere Rotation 18

19 Lecture-Tutorial (LT): Position (pp. 1-2) Work with a partner! Read the instructions and questions carefully. Discuss the concepts and your answers with one another. Come to a consensus answer you both agree on. If you get stuck or are not sure of your answer, ask another group. If you get really stuck or don t understand what the LT is asking, ask for help. 19

20 In what Celestial Sphere Rotation direction is the observer 1 Star B 2 Star A 2 facing? Celestial Sphere 3 1 Celestial Sphere 4 1. toward the South 2. toward the North 3. toward the East 4. toward the West 4 Figure 2 3 Celestial Sphere Rotation Horizon 20

21 Where would the observer look to see the star indicated by the arrow? Celestial Sphere Rotation 1 Celestial Sphere Star B 2 Star A 2 Celestial Sphere 3 Horizon A. High in the Northeast B. High in the Southeast C. High in the Northwest D. High in the Southwest 4 Figure 2 Celestial Sphere Rotation 21

22 We measure the sky using angles 22

23 Angular Measurements Full circle = 360º 1º = 60ʹ (arcminutes) 1ʹ = 60ʺ (arcseconds) 23

24 Quiz The angular size of your finger at arm s length is about 1. How many arcseconds is this? A. 60 arcseconds B. 600 arcseconds C = 3,600 arcseconds 24

25 Lecture-Tutorial (LT): Motion (pp. 3-6) Work with a partner! Read the instructions and questions carefully. Discuss the concepts and your answers with one another. Come to a consensus answer you both agree on. If you get stuck or are not sure of your answer, ask another group. If you get really stuck or don t understand what the LT is asking, ask for help. 25