ASTR 1120 General Astronomy: Goals of the day Stars & Galaxies • This Course - basic info review • Order of Magnitude Prof. Rosalba Perna Astronomy – Reasonable estimates TA:Thomas Rogers • Size Scales - getting used to astronomy • Light year http://amalfi.colorado.edu/~rosalba/astro1120/astro1120.html – Measuring distances in astronomy MAKE SURE TO GO OVER THE SYLLABUS (if you haven’t already done so) Who should take this course? MATH REVIEW SESSION : • No prerequisites, Will you attend it? aimed at non-science majors A.YES • No lab credit • Moderate amounts of quantitative work B. NO (algebra) In the process of coordinating with other classes • More quantitative course – ASTR 1040
Required Text Course Information The Cosmic Perspective COURSE WEB PAGE: by Bennett et al., 2007, 5 th ed http://amalfi.colorado.edu/~rosalba/astro1120/astro1120.html You can find Includes: announcements, Access to textbook website www.masteringastronomy.com , assignments and Ebook (animations, etc), and handouts, lecture notes, SkyGazer planetarium and other useful things software. there You will need your own Grades will be shown on `masteringastronomy’ account! CULearn Most homeworks require it Course ID: ASTR11202009A Come talk with us How to succeed in this course • Prof. Rosalba Perna’s office hours: Tue: 1pm-2pm; Th: 1pm-3pm in JILA Tower 506A (phone: 303-492- • PUT IN THE TIME: 0389) rosalba@colorado.edu 3 credits at CU = 6-9 hours outside of the classroom • TA Thomas Rogers office hours: Wed, Fri: 2pm-3:30pm in Duane D1B31 • Read the textbook (phone: 720-308-9382). sections as assigned in Thomas.Rogers@colorado.edu class, discuss with friends, do homeworks, • Or call or email (any of us) to make come to an appointment! class • Come see us during office hours!
Clickers Observatory Nights GRADED clicker questions will start NEXT WEEK. Remember to bring your clicker to class always. • Starting Wed Sept 2nd at 8:30pm, then about every 2 weeks Clicker questions TODAY UNGRADED . • Sommers-Bausch Observatory (next to Fiske): 16” and 18” telescopes • 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 Clicker Test • What is the nationality of your professor? • What class are you in? • A) French • A) Freshman • B) Spanish • B) Sophomore • C) Argentine • C) Junior • D) Italian • D) Senior • E) Greek • E) Other
Reading Clicker Question THE COSMIC CALENDAR If the history of the entire universe was condensed into a single year, the earliest humans (hominids) would have appeared about: A. September 1 B. December 1 C. December 30 D. 9 p.m. December 31 (3 hours before year- end) E. 11:59:30 p.m. December 31 (30 seconds before year-end) More on order of magnitude Order of Magnitude Astronomy Astronomy How many piano tuners are • Astronomy frequently deals with very BIG there in Boulder County? numbers • When dealing with really big quantities, the A. 2 small details become trivial – For example, when we say that the nearest galaxy B. 20 is 2 million (2,000,000) light-years away, does it C. 200 really matter if its actually 2,000,001? 2,000,100? – How far is it to drive from here to Los Angeles? D. 2000 (centimeters won’t matter…) E. Too many to count! What’s a factor of � between friends?
Start with known facts and More reasonable estimates reasonable guesses Population of Boulder County? • How long does it take to tune a piano? – ~300,000 people • How many people have a piano? – 3-4 hours? – 1 in 30? = 2 tunings per day • Could be off but probably not by much! • 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 Scales in the Universe: Scale models of the Universe our Cosmic Address Earth • Scale Sun as a grapefruit (1:10,000,000,000) Sun/Solar System Milky Way Galaxy Local Group Local Supercluster
What about distances from the Moving out of the solar system Sun on the same scale? • On this scale, the nearest stars would • Earth = tip of ball point be a system formed by a cantaloupe, a pen, 15 meters (49 feet) small apple and a kiwi fruit, located in – Moon = 4 cm away from the middle of Alaska (with solar system earth • Mars = tip of ball point in Boulder) pen, 23 meters (75 feet) • Jupiter = marble, 78 meters (255 feet) • There is essentially nothing in between!! Yet Another Scale for Everything New Scale for the Galaxy: Else • Galaxies are 10” paper • Stars are microscopic - located a few mm apart plates • Milky Way galaxy is 100 meters in diameter, contains 100,000,000,000’s (100’s of billions) of • Milky Way and nearest neighbor Andromeda) stars are 5 meters apart 1 to 10^19 scale - MW=100 m 3000 yr to counts all the stars in the MW, one per second • Galaxy groups and clusters contain 10’s to 1000’s of galaxies Solar system: dot ~20 meters away from center
Which of these are the most likely? • Superclusters 50 meters across (size of buildings in our A. Two planets colliding scale model) are B. Two stars colliding the largest C. Two galaxies colliding structures we see D. None of the above… there’s too much space! • Observable universe is about In this image, each dot is an entire size of Boulder galaxy county on this scale Clicker Question Light-year: which of the following Measuring cosmic distances sentences makes sense? (the • Most useful measure is based on the speed others are nonsense) of light = 300,000 km/sec – Light-year = the distance light travels in a year A. We’ll wait light-years before Mars is as close as = ~ 10 trillion kilometers = 10 16 m it is tonight. B. The Galileo spacecraft has traveled 30 light- • Like saying “I live 30 min from Boulder” years since its launch in 1989. C. The globular cluster M13 is located 16,000 light- • Constant speed for light traveling in space years away from Earth. D. The next generation of the Space Shuttle will be • Nothing travels faster through space able to travel 1.3 times the speed of light.
Measuring Distances with Light: • Earth-Moon = 1.5 light-seconds • Earth-Sun (a.k.a. astronomical unit, or AU) = 8 light-minutes Not A: light-years measure distance, not time. • Solar system = light-hours Not B: Light travels 1 light-year in 1 year. Nothing travels faster than light! C: correct! Not D: Same as B. Nothing can travel faster than the speed of light. Clicker Question • Nearest stars = several light-years • Milky Way= 100,000 light-years = 10 5 ly • A radio message from outer space – Galactic Center is 28,000 light-years away arrived today which was sent from planet Buff on the day you were born. The • Local group = several million light-years =10 6 ly friendly aliens sending you the birthday • Observable universe = 14 billion light-years = 1.4 x 10 10 message live: ly 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
Over astronomical distances, even light takes a lot of time (from a human’s perspective!) to travel between the stars • Answer: you are probably between 10 and 90 years old. Objects at distances This means that what we SEE in the distant between 10 and 90 light-years away from us are relatively close-by stars in universe is light that has traveled a long the Milky Way. time. • The solar system is light-hours in size Our image of the universe is a delayed • The Local group is millions of light- image . years in size In looking out into space, we are looking back in time! Image of the Orion nebula, 1500 ly away Look Back Time 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 = 0.00001 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)
Clicker Question When studying the Universe, it is Last night we saw a bright supernova explode in impossible to separate space and time the Andromeda galaxy (the other big galaxy in the local group). The remnants from such • The image of a explosions disperse in about 10,000 years. galaxy spreads A. The supernova remnant still exists now, and across 100,000 we will watch it disperse over the next 10,000 years of time Earth years. B. In reality, the supernova remnant has already dispersed, but we will watch it disperse over • Try to think of what the next 10,000 Earth years. we SEE NOW as C. The image of the supernova dispersing will not different from what reach us for another 2 million years. may EXIST now D. We will never see the supernova remnant because it has already dispersed. • Answer: B Discussed so far • This galaxy is millions of light-years away from us. The light left the galaxy millions of • Cosmic Distances years ago and only arrived yesterday. In • Light-Year vs Year the intervening time, the supernova remnant has dispersed and no longer • Look Back Time exists today. But the light that left on the day after the explosion will arrive here today and we Make sure to become familiar with these concepts! can see that.
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