Goals of the day. Who should take this course? MATH REVIEW SESSION: ASTR 1120 General Astronomy: Stars & Galaxies

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1 ASTR 1120 General Astronomy: Stars & Galaxies Prof. Rosalba Perna TA:Thomas Rogers MAKE SURE TO GO OVER THE SYLLABUS (if you haven t already done so) Goals of the day This Course - basic info review Order of Magnitude Astronomy Reasonable estimates Size Scales - getting used to astronomy Light year Measuring distances in astronomy Who should take this course? No prerequisites, aimed at non-science majors No lab credit Moderate amounts of quantitative work (algebra) More quantitative course ASTR 1040 MATH REVIEW SESSION: Will you attend it? A.YES B. NO In the process of coordinating with other classes

2 Course Information COURSE WEB PAGE: You can find announcements, assignments and handouts, lecture notes, and other useful things there Grades will be shown on CULearn Required Text The Cosmic Perspective by Bennett et al., 2007, 5 th ed Includes: Access to textbook website Ebook (animations, etc), and SkyGazer planetarium software. You will need your own `masteringastronomy account! Most homeworks require it Course ID: ASTR A How to succeed in this course PUT IN THE TIME: 3 credits at CU = 6-9 hours outside of the classroom Read the textbook sections as assigned in class, discuss with friends, do homeworks, come to class Come talk with us Prof. Rosalba Perna s office hours: Tue: 1pm-2pm; Th: 1pm-3pm in JILA Tower 506A (phone: ) rosalba@colorado.edu TA Thomas Rogers office hours: Wed, Fri: 2pm-3:30pm in Duane D1B31 (phone: ). Thomas.Rogers@colorado.edu Or call or (any of us) to make an appointment! Come see us during office hours!

3 Observatory Nights Starting Wed Sept 2nd at 8:30pm, then about every 2 weeks Sommers-Bausch Observatory (next to Fiske): 16 and 18 telescopes Clickers GRADED clicker questions will start NEXT WEEK. Remember to bring your clicker to class always. Clicker questions TODAY UNGRADED. Not mandatory, but you can get extra credit towards your grade (Fill out summary sheet available at observatory) Signup required on CULearn website Clicker Test What class are you in? Clicker Test What is the nationality of your professor? A) Freshman B) Sophomore C) Junior D) Senior E) Other A) French B) Spanish C) Argentine D) Italian E) Greek

4 Reading Clicker Question If the history of the entire universe was condensed into a single year, the earliest humans (hominids) would have appeared about: THE COSMIC CALENDAR A. September 1 B. December 1 C. December 30 D. 9 p.m. December 31 (3 hours before yearend) E. 11:59:30 p.m. December 31 (30 seconds before year-end) Order of Magnitude Astronomy Astronomy frequently deals with very BIG numbers When dealing with really big quantities, the small details become trivial For example, when we say that the nearest galaxy is 2 million (2,000,000) light-years away, does it really matter if its actually 2,000,001? 2,000,100? How far is it to drive from here to Los Angeles? (centimeters won t matter ) What s a factor of! between friends? More on order of magnitude Astronomy How many piano tuners are there in Boulder County? A. 2 B. 20 C. 200 D E. Too many to count!

5 Start with known facts and reasonable guesses Population of Boulder County? ~300,000 people How many people have a piano? 1 in 30? Could be off but probably not by much! More reasonable estimates How long does it take to tune a piano? 3-4 hours? = 2 tunings per day How many pianos? ~10,000 pianos in Boulder County How often do you need to tune a piano? Once a year?? 10,000 piano tunings/year Earth Scales in the Universe: our Cosmic Address Scale models of the Universe Scale Sun as a grapefruit (1:10,000,000,000) Sun/Solar System Milky Way Galaxy Local Group Local Supercluster

6 What about distances from the Sun on the same scale? Earth = tip of ball point pen, 15 meters (49 feet) Moon = 4 cm away from earth Mars = tip of ball point pen, 23 meters (75 feet) Jupiter = marble, 78 meters (255 feet) Moving out of the solar system On this scale, the nearest stars would be a system formed by a cantaloupe, a small apple and a kiwi fruit, located in the middle of Alaska (with solar system in Boulder) There is essentially nothing in between!! New Scale for the Galaxy: Stars are microscopic - located a few mm apart Milky Way galaxy is 100 meters in diameter, contains 100,000,000,000 s (100 s of billions) of stars 1 to 10^19 scale - MW=100 m 3000 yr to counts all the stars in the MW, one per second Yet Another Scale for Everything Else Galaxies are 10 paper plates Milky Way and nearest neighbor Andromeda) are 5 meters apart Galaxy groups and clusters contain 10 s to 1000 s of galaxies Solar system: dot ~20 meters away from center

7 Superclusters 50 meters across (size of buildings in our scale model) are the largest structures we see Observable universe is about size of Boulder county on this scale In this image, each dot is an entire galaxy Which of these are the most likely? A. Two planets colliding B. Two stars colliding C. Two galaxies colliding D. None of the above there s too much space! Measuring cosmic distances Most useful measure is based on the speed of light = 300,000 km/sec Light-year = the distance light travels in a year = ~ 10 trillion kilometers = m Like saying I live 30 min from Boulder Constant speed for light traveling in space Nothing travels faster through space Clicker Question Light-year: which of the following sentences makes sense? (the others are nonsense) A. We ll wait light-years before Mars is as close as it is tonight. B. The Galileo spacecraft has traveled 30 lightyears since its launch in C. The globular cluster M13 is located 16,000 lightyears away from Earth. D. The next generation of the Space Shuttle will be able to travel 1.3 times the speed of light.

8 Measuring Distances with Light: Earth-Moon = 1.5 light-seconds Not A: light-years measure distance, not time. Not B: Light travels 1 light-year in 1 year. Nothing travels faster than light! Earth-Sun (a.k.a. astronomical unit, or AU) = 8 light-minutes Solar system = light-hours C: correct! Not D: Same as B. Nothing can travel faster than the speed of light. Nearest stars = several light-years Milky Way= 100,000 light-years = 10 5 ly Galactic Center is 28,000 light-years away Local group = several million light-years =10 6 ly Observable universe = 14 billion light-years = 1.4 x ly Clicker Question A radio message from outer space arrived today which was sent from planet Buff on the day you were born. The friendly aliens sending you the birthday message live: A. In the Solar System B. From a close-by star in the Milky Way C. In Andromeda, the nearest major galaxy D. In a galaxy outside the local group

9 Answer: you are probably between 10 and 90 years old. Objects at distances between 10 and 90 light-years away from us are relatively close-by stars in the Milky Way. The solar system is light-hours in size The Local group is millions of lightyears in size Over astronomical distances, even light takes a lot of time (from a human s perspective!) to travel between the stars This means that what we SEE in the distant universe is light that has traveled a long time. Our image of the universe is a delayed image. In looking out into space, we are looking back in time! Look Back Time Image of the Orion nebula, 1500 ly away What we SEE is always delayed by the speed of light. In the classroom, our view of each other is only about 10-5 seconds old, so we barely notice (10-5 sec = sec) Satellite communications - noticeable delays The image of the Sun is old? Analogy: what we hear is delayed by the speed of sound - more familiar in our everyday lives (e.g. lightening-thunder delay)

10 When studying the Universe, it is impossible to separate space and time The image of a galaxy spreads across 100,000 years of time Try to think of what we SEE NOW as different from what may EXIST now Clicker Question Last night we saw a bright supernova explode in the Andromeda galaxy (the other big galaxy in the local group). The remnants from such explosions disperse in about 10,000 years. A. The supernova remnant still exists now, and we will watch it disperse over the next 10,000 Earth years. B. In reality, the supernova remnant has already dispersed, but we will watch it disperse over the next 10,000 Earth years. C. The image of the supernova dispersing will not reach us for another 2 million years. D. We will never see the supernova remnant because it has already dispersed. Answer: B This galaxy is millions of light-years away from us. The light left the galaxy millions of years ago and only arrived yesterday. In the intervening time, the supernova remnant has dispersed and no longer exists today. But the light that left on the day after the explosion will arrive here today and we can see that. Discussed so far Cosmic Distances Light-Year vs Year Look Back Time Make sure to become familiar with these concepts!

11 For next class meeting, reading...remains on the entire Ch. 1 Make sure you familiarize yourself also with the (more mathematical) material in the boxes. Make sure you have completed the (UNGRADED) Tutorial on Mastering Astronomy. IF you have problems, please let us know!