Lecture3ASTJan24 - Schedule : Announcements: Syllabus...

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1 Schedule : Announcements: Syllabus update. Q’s about ASN? New slide in SMT. AST1002 Lecture 3 Follow up on some material from last time. Treat essentials of Ch. 2. Light. Comment: Lectures are a guide, but not everything. The book, materials in our Bb library, HW and Quizzes, and questions when things aren’t clear are the best plan! How did Kepler figure out that Mars had an elliptical orbit? Triangulation! Some facts and assumptions: ) he Earth’s orbit is nearly circular so the 1) The Earth s orbit is nearly circular, so the distance between Earth and the Sun can be assumed to be 1 AU. 2) Mars’ orbit is the most eccentric of all the planets (lucky for Kepler). perihelion = 1.381 497 AU aphelion = 1.665 861 AU Let’s do a quick Keplerian example: Kepler sees in Tycho’s data that at a certain time, the Sun, Earth, and Mars make a right triangle, and Tycho recorded the angle θ 1 . Kepler knows the distance between the sun and the earth is 1 AU. AU D Mars θ position #1 D Mars (#1) = AU*Tan( θ ) Assume: Earth is in circular orbit of 1 AU radius. Know: high school trig! Kepler sees in Tycho’s data later on that the Sun, Earth, and Mars again make a right triangle in a different configuration, and Tycho recorded the angle θ 2 . AU D Mars (#1) θ 1 position #1 position #2 D Mars (#2) θ 2 D Mars (#1) = AU*Tan( θ 1 ) D Mars (#2) = AU*Tan( θ 2 ) You can see that the second angle is less, so the distance between Mars and the Sun is less. θ 1 = 59 ο θ 2 = 54 ο 1.381 AU 1.665 AU In actual #’s,
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2 Light – the main tool of astronomy • See an object adar ounce light off of an object • Radar – bounce light off of an object • Composition – Adsorption, emission • Temperature – “Black body radiation” • Speed of motion – Doppler effect, “red shift”, “blue shift” • Detect Mass – gravitational lensing • Magnetic field – changes in spectrum F = kq 1 q 2 /r 2 q 1 q 2 Coulomb’s law (just like Newton’s law, but things can repel as well as attract.) When charges “wiggle”, they give off a light wave.
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This note was uploaded on 03/18/2012 for the course ASTRO AST1002 taught by Professor Jamesbrooks during the Spring '12 term at Florida State College.

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Lecture3ASTJan24 - Schedule : Announcements: Syllabus...

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