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Physics 20A Week One Notes

by: Joyce Nguy

Physics 20A Week One Notes Physics 20A

Joyce Nguy
GPA 3.82
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Here are my week's worth of notes in Professor Tammy Smecker-Hane's class. Happy studying!
Class Notes





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This 5 page Class Notes was uploaded by Joyce Nguy on Saturday January 23, 2016. The Class Notes belongs to Physics 20A at University of California - Irvine taught by SMECKER-HANE, T. in Summer 2015. Since its upload, it has received 18 views. For similar materials see INTRO TO ASTRONOMY in Physics 2 at University of California - Irvine.


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Date Created: 01/23/16
1/4/15     Intro to Astro ­ Syllabus    1. smartwork homework 0 and 1 due friday   2. smartwork homework 2 due tues, jan 12  3. syllabus stuff   a. we are lecture A   b. username for web: p20A password: exploreASTRO  c. office hours 10 an­12 wednesday   4. material to be covered:   a. moon phases, planets, light, eclipse  5. log on to triple eee message board and tell about yourself   6. textbook: 21st century astronomy (4th edition)   a. has smartwork registration code   b. ebook ­ one that expires after a year or lasts forever   c. comes with study space ­ website with simulations   7. HOMEWORK DUE FRIDAY 9:00 PM   8. SECTION REQUIRED   9. QUIZZES EVERY OTHER WEEK ­ MULTIPLE CHOICE   a. similar to exams ( all exams MULTIPLE CHOICE)   b. ⅓ questions will be numerical, ⅔ conceptual   c. on sunday, quiz is 45 min. any time between close of class friday to sunday at  11:00 pm ON EEE QUIZ  10. 35% final exam, 30% exams 1 & 2, 15% average homework score (highest 13 out of 15  scores), 15% average quiz score (highest 6 out of 7), 5% participation ­ need SEVEN  CLASS PARTICIPATION POINTS ( POST ON MESSAGE BOARD FOR A POINT IF  TOO SHY)   11.  Smartwork enroll ­ use UCI email address, include UCI student ID number,   12. Homework   a. FIVE CHANCES AT EVERY QUESTION but 15% less for every wrong answer   b. ALWAYS CURVED   c. in smartwork, if you answer in numerical answer, you need to give three sig figs  (if 1.23456, then 1.23)  d. 0 is not sig fig, not 0.23, 0.234  e. don’t have to memorize ANY FORMULAS, on the FORMULA SHEET  f. CAN WORK AHEAD ON HOMEWORK   13. Quizzes  a. 5­7 questions   b. based on the readings  14. EXAM DATES   a. Jan 27 ­ Exam 1   15. Makeup policy   a. no makeup homework and quizzes  16. USE MESSAGE BOARD FOR COMMUNICATION ­ EEE   17. calc­ can’t be graphing calc   18.  deadline ­ introduction about yourself due by week one ­  two sentences requirement  intro on messageboard ­ hit the reply button   19.  IF NOT COVERED IN LECTURE WON’T BE IN ANYTHING ELSE     Lecture 1     1. what is modern astronomy?   a. much more than cataloguing objects in the sky   b. how do stars (matter and energy) work?   c. how do the laws of physics apply on different scales: atoms, molecules, humans,  planets, stars and galaxies?  2. our place in the universe  a. earth: 3rd rock from the sun   i. two rocky planets interior to earth : mercury and venus­ (venus is twin  planet, mostly carbon dioxide)   ii. right distance for liquid water to exist ­ primary ingredient for life  b. sun: an average star   c. average spiral galaxy Milky Way ­ about 100 billion stars  d. local group: the approximately 40 galaxies within a 3 million light year radius  around the Milky Way   e. nearest spiral galaxy ­ Andromeda   f. virgo supercluster: a large grouping of galaxy groups and galaxy clusters   g. the universe: 13.7 billion years old, possibly infinite in size   3. the speed of light   a. the sizes and distances in astronomy are vast!   i. distance between earth and sun = 1.5 x 10^11 m   ii. diameter of the Milky Way = 9.5 x 10^20 m   b. in astronomy, we use the distance that light travels in one year (1 year = lyr) as  handy measure of distance   c. as an analogy, we may say a friend’s house is two hours away   d. light travels very fast; around the Earth in 1/7 second!   e. light travels at a speed equal to   i. c (speed of light) = 3 x 10^8 m/s = 3 x 10^2 x 10^6   ii. c = 300 million m/s  f. light year: distance light travels in one year  g. definition of speed: c=d/t   h. ex: time it takes light to travel from earth to sun   i. t=d/c = (1.5x10^11 m) / (3x 10^8 m/s)   ii. t = .5 x 10^3 s   i. ex: light travels in one year distance?   j. C=d/t   k. convert year into seconds ­ 1(3x10^8 m/s) 1 yr (365 days/1 yr) x (1day/24 hr) (1  hr/60 min) (1min/ 60 sec)   l. d = 9.5 x 10^15 m   m. 1 light year = 9.5 x 10^15 m   n. distance to the nearest star Proxima centauri, a binary star companion of the  brighter star alpha centauri, is 4.2 lyr ( so if you look at it, you are looking at it like  it was 4.2 years ago, looking back in time in the night sky)   4. light travel times   a. light takes:   i. 1 ¼ seconds to arrive from moon   ii. 8.3 minutes to arrive from sun   iii. 5.5 hours to pluto from the sun  iv. 4.3 year to nearest star   v. 2.9 million yrs to andromeda   5. science is a process  a. patterns in nature usually hold the clues to understanding nature  b. science is a method for studying the patterns to understand nature   c. the scientific method   i. idea  ii. hypothesis  iii. prediction   iv. test  6. science must be tested  a. all scientific knowledge is provisional   b. all scientific theories must be able to be falsified and rejected  c. as new data is available, might be proven false  7. an important assumption   a. cosmological principle: “nothing special about us ­ any point in universe”        1/6/16    Lecture 2   1. the celestial sphere  a. how the night sky moves due to:   i. earth’s daily rotation (once every 24 hours) and   ii. earth’s yearly orbit around the sun   b. the reason for the seasons  c. an  imaginary sphere with the stars having fixed locations on it and the earth lying  at the center of the sphere   d. star’s coordinates are just the projection of earth’s longitude and latitude (poles  and equator) into space  e. points on sphere correspond to specific directions in space   2. the observer’s sky   a. an observer on earth sees only half of the celestial sphere at a given time  b. some key positions in an observer’s sky are:   i. horizon ­ the great circle where the earth meets the sky (H ­> H’ ­> H)  ii. zenith direction ­ direction right above us (z)   iii. meridian ­ the great circle on which lies the N pole, S pole and the  observer’s zenith (orange line)   iv. ecliptic plane ­ the plane of our solar system where the sun and planets  will lie.  the path the sun appears to take across the celestial sphere in  one year  3. the celestial sphere  a. appears to rotate once around the north and south celestial poles each day  b. celestial equator: the great circle lying midway between poles  c. ecliptic: path of the sun across the celestial sphere, inclined 23.5 degrees to  earth’s equator ­ WHY WE HAVE SEASONS   4. night sky map   a. because polaris, the north star, is very near the north celestial pole, over the  course of a night the celestial sphere appears to rotate around Polaris  b. stars rise in the east and set in the west moving a rate of 360 degrees/24 hrs =  15 degrees/hr   c. circumpolar stars ­ rotate and can see all night long  5. constellations   a. are arbitrary patterns of stars in the sky that are products of human imagination   b. stars in a constellation are usually not even at the same distance from us and  hence they are unrelated to one another   c. the science of astronomy shattered ancient mystical views of the heavens by  explaining the motions of the stars and planets in the night sky   6. earth rotates on its axis   a. as viewed from above the north pole, earth rotates counterclockwise on its axis  once every 24 hrs   b. the earth orbits counterclockwise around the sun once every 1 year  (approximately 365.25 days = 12 months)  7. earth orbits the sun   a. the sun’s motion on the ecliptic reflects earth’s orbit around the sun   b. as earth moves, the sun is seen against different constellations ­ the  constellations of the zodiac  8. frames of reference   a. an observer sees things from a specific frame of reference   b. relative motion between you and the object you’re observing is important   c. observers located at different latitudes on earth see   i. different parts of the sky   9. the size of earth’s orbit  a. earth’s orbit is nearly circular   b. average distance to sun is astronomical unit or AU   c. 1 AU =   10. earth’s axis   a. not perpendicular to ecliptic plane   b. it is inclined by angle of 23.5 degrees  c. angle of sunlight is closer to perpendicular in summer and more energy falls on a  unit area of the earth’s surface than in winter   d. when northern hemisphere is in summer, the southern hemisphere is in winter  11. precession   a. currently the north celestial pole is near the bright star Polaris  b. earth’s axis wobbles, like the axis of a spinning top, with a period of 26,000 years  12.     


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