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# AS101.docx

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Department
Astronomy
Course
AS101
Professor
Shelley Mc Gill
Semester
Winter

Description
AS101 Lecture 2: A sense of scale Two ways to write numbers: 1. Scientific notation (powers of 10(次方))  Place the decimal after the first nonzero digit  Count the number of places that the decimal point moved  If the decimal moves to the left, the power of 10 is positive, right – negative. 2. Use different units  1 au(astronomical unit)= average distance between earth and sun= 150 million km(1.5*10 的 8 次方)  1 ly (light-year)= the distance light travels in one year= 9.46* 10 的 12 次方  1 pc(parsec) = 3.26ly= 3.09* 10 的 13 次方  1 Mpc (megaparsec) = 1 million parsecs Ex : Avg. distance between the Sun and Jupiter =5.2au Distance to the nearest star other than the Sun: 4.37ly or 1.34 pc Distance to Andromeda galaxy (one of the our galaxy’s near neighbours): 2.6 million ly or 0.78 Mpc. A sense of scale: distance How far away is the nearest star – Alpha Centauri = 4.4 trillion km. Measure in scale km=1 billion km. So 4.4 trillion km = 4400 scale km A sense of scale: time th Jan 16 class Earth turning from west to east but sphere turning from east to west. Therefore, the sky doesn't change because it is opposite. Assignment 1  Quizzes Home  Summary  Submissions Selected  Reports Sheng Lan (username: slan3) To Submissions Attempt 1 Written: Jan 21, 2013 4:06 PM - Jan 21, 2013 4:32 PM Submission View Your quiz has been submitted successfully. Question 1 1 / 1 point What is the definition of an astronomical unit? Question options: A) Any large number. B) The distance that light travels in one year The average distance between the Earth and the C) sun D) The distance between the sun and Alpha Centauri. The average distance between the Earth and the E) Moon. Question 2 1 / 1 point The number 7.14 X 10 is equivalent to which of the following? Question options: 7,140 714,106 75,684 7,140,000 0.00000714 Question 3 1 / 1 point Using what you have learned, rank the following objects from smallest to largest (1=smallest,4=largest): Earth, Milky Way Galaxy, solar system, sun. __3__ Solar System __1__ Earth __4__ Milky Way Galaxy __2__ Sun Question 4 1 / 1 point Rank the following objects from smallest to largest (1=smallest): galaxy, filament, cluster, planet, star. __2__ Star __1__ Planet __4__ Cluster __3__ Galaxy __5__ Filament Question 5 2 / 2 points The sun is about 400 times farther from the Earth than the moon is. How many seconds does it take light from the moon to reach the earth? (Hint: remember that we figured out in class how long it takes light to reach us from the sun.) Answer: 1.3 in diameter, what is its diameter in millimeters? (HINT: 1km=1000m, and 1m=1000mm. Enter the answer in scientific notation using the blanks below.) Answer: 3.47544x10^9 Based on what you have learned about the relative sizes of objects and the distances between them, select all of the correct statements from the following list. Question options: Filaments, voids, and walls are structures within galaxies. The sun is about 100 times the diameter of Earth. Our galaxy is thousands of light-years across. Light takes more than a thousand years to reach us from the nearest star other than the sun. Galaxies are the largest structures in the universe. The sun is very large for a star. The solar system is part of the Milky Way galaxy. Question 1 1 / 1 point Which of the following best describes the constellations as the word is used by modern astronomers? Question options: They are twelve patterns of stars along the ecliptic, named after mytholoical figures. They are 88 groups of stars, with members of each group physically close to each other in space. They are 88 well-defined regions on the celestial sphere. They are 88 patterns of stars named after mythological figures and animals Question 2
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