Astronomy 1 Fall 2016

Transcription

1 Astronomy 1 Fall 2016 Lecture 17; November 29, 2016

2 Announcements Final grade will be calculated as stated on the course web page. The final exam is 40% of your total grade. Gaucho Space does not show the cumulative grade. Office hours this week: TODAY, Tuesday: Professor Martin 3:15-4:00 pm Wednesday: Mr. Burke 2:00-3:30 Friday: Ms. Ho 11:30-12:30 (PSR) Friday: Mr. Burke 2:30-3:30 (PSR) If you are unsure of the answer to any midterm #2 problem, please come see us. No class this Thursday. Use the time to study.

3 Final Exam (Tuesday Dec. 6 th, 4-6 pm) Bring a large, red ParScore, calculator, and #2 pencil. NOTE: COMPLETELY FILL IN THE BUBBLES! An opportunity to demonstrate that you ve learned material you missed on the midterms. Cumulative & focused on concepts. Covers chapters 22 & 23 and 1-8, 10, multiple-choice questions 17 questions on new material from ch ; think of these as a third midterm 68 review questions (roughly 4 from each of the chapters)

4 Planets, Stars, Galaxies, and the Universe are governed by the same laws of physics as laboratory experiments. Can you draw some analogies?

5 The Study of Planets, Stars, Galaxies, and the Universe is intimately connected to atoms Can you give some examples?

6 Light How long does it take sunlight to reach Earth? Travel to the center of the Galaxy? How can astronomers take pictures of infant galaxies less than a billion years old? What is light? How do we know? How do atoms emit and absorb light? What are the properties of the light emitted by opaque sources such as stars, dust grains, planets, gas in galaxy clusters, etc? Can you give an example of a light source that is not a blackbody?

7 Your Universe: Structure of the Solar System How do you know the earth spins? Are you sure the Earth orbits the Sun (and not vice-versa)? Do the nearest stars beyond the Sun have planets? Do most stars like the Sun have planetary systems? Are they like the Solar System?

8 Review: The Celestial Sphere Why does the night sky change? 1. Earth s rotation 2. Earth s orbital motion about the Sun 3. The moon s orbit around the Earth 4. The orbits of the outer planets about the Sun 5. The precession of the Earth s spin axis

9 Earth s Rotation

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11 Celestial Coordinates

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14 Celestial Pole

15 Precession of Earth s Rotation Axis

16 Earth s Orbit E W Because of the Earth s motion along its orbit, we don t see the same stars overhead at the same time each night. If Cygnus is overhead at midnight in July, then 1. where would you see it in September at midnight? a) Draw a line toward Cygnus b) Draw the horizon c) So, West of the zenith 2. and when in September would Cygnus be overhead? Earlier. 24 hours of RA / 12 months So the RA that s overhead at midnight must shift by 2 hours per month

17 Let s Check (iclicker Question)

18 Wandering of Mars in 2016 East West South When was Mars in retrograde motion? Retrograde motion was central to the debate about Earth s place in the solar system. Note: The green line above is the ecliptic.

19 North Celestial Equator East West Just Checking Ecliptic Ecliptic Plane

20 Retrograde Motion of Planets (heliocentric perspective)

21 Galileo s Discoveries with a Telescope (supported the heliocentric model) The year 1610 ended a debate dating back thousands of years. 1. Phases of Venus 2. Moons of Jupiter

22 Changing Appearance of Venus in a Heliocentric Model

23 Your Universe: Age of the Solar System How old are oldest meteorites? The Earth? In the mid 1800s, Lord Kelvin and Hermann von Helmholtz argued that the Sun could not be more than years old. What was their argument? What objects do shine by Kelvin-Helmholtz contraction? Why will the Sun actually remain at roughly 1 solar luminosity for years? What will happen to the Sun then?

24 The Hertzsprung-Russell Diagram Stars on the Main Sequence are all burning H in their cores. What property sets them apart? Degeneracy pressure sets the minimum mass of a star. Why? He ignition White dwarfs Which stars spend the least time on the main sequence?

25 iclicker Question

26 Your Universe How was the carbon and oxygen in your body made? What about the nitrogen? How about the calcium and phosphorus? How do elements get out of stars? Stellar winds Thermal pulses & planetary nebulae Supernova explosions

27 iclicker Question

28 iclicker Question

29 iclicker Question

30 Since Midterm 2 Key Topics from ch. 22 Milky Way Galaxy Contains ~2x10 11 stars Sun is in a nearly circular orbit 8 kpc from the center Stars (Pop I) in disk are young and metal rich Stars in halo (Pop II) are older and metal poor The central bulge has a radius of 1 kpc and a mass about 1000 times larger than the supermassive BH. Is still growing today via mergers with other galaxies Rotation curves indicate nonluminous matter Spiral arms are Density waves Locations where gas clouds pile up and trigger star formation Traced by dust lanes and HII regions

31 Since Midterm 2 Key Topics from ch. 23 The Universe contains billions of galaxies Why wasn t this clear to Einstein as late as 1920? The importance of Hubble s discovery of Cepheids in Andromeda. The cosmic distance ladder Discovery of the expansion of the Universe Hubble s Law Cosmological redshift Redshift as a distance measurement Large-scale structure of the galaxy population Groups, clusters, and voids Cosmological principle Formation of galaxies Small galaxies merged into larger galaxies We can see galaxies at a time when the Universe was less than onetenth its current age (13.8 billion years) Evolution of galaxies Galactic winds Mergers (of galaxies and clusters)

32 The Milky Way Galaxy Was probably visible to Paleoindians living on Santa Rosa island some 13,000 years ago. How can it be that by the time North America was colonized by Europeans in the mid-18 th century, scholars of the time believed the Solar System was at the center of the Galaxy? How did a California astronomer (Robert Trumpler of Lick Observatory) and Harvard astronomers (Henrietta Leavitt and Harlow Shapley) map out the true size and shape?

33 A Universe of Galaxies The idea that vast collections of stars lie beyond the Milky Way dates back to at least 18 th century philosophers. Why then were Shapley and Heber Curtis (another California astronomer at Lick Observatory) debating the nature of spiral nebulae on a national stage in 1920? Why did Edwin Hubble s images of the Andromeda Nebula resolve this debate in 1923? [Another California astronomer, working on Mt. Wilson though]

34 Hubble s 2 nd Remarkable Discovery: All the Galaxies are Flying Away from Us! Hubble s Law v = H 0 d v = shift of spectral lines in km/s d = distance to galaxy in Mpc H 0 = fitted constant of roughly 73 km/s/mpc

35 The Cosmological Principle states that the Universe is homogeneous and isotropic on large scales. Is this supported by observations? How? Is the Universe the same at all times? Well, no, and this surprised many scholars!

36 The Universe is a Dynamic Place Can you give some examples of objects that move (and why they move)? What is surprising about the motions of stars within galaxies? What is surprising about the motion of galaxies with respect to one another? Where are new stars born?s

37 Astro 1 The End? My hope is that it s actually a beginning that cultivates your notions about the universe and your place within it!