Unit 1: Astronomy Basics - Powers of 10, Constellations, and Celestial Bodies, Study notes of Physics

Download Unit 1: Astronomy Basics - Powers of 10, Constellations, and Celestial Bodies and more Study notes Physics in PDF only on Docsity! Tuesday, 23 September, 2008 PHYS-1060 (1) Fall 2008 3:30-4:45pm Tu Th 1104 Rood Dr. Philip Edward Kaldon Western Michigan University Unit 1 Powers of 10 (magnitudes) 1 – ME, You, The Sun 10 – planets (in our solar system) 100 – years of life 1000 – miles to New York or Florida -- years of Civilization 10,000 – kilometers size of Earth 100,000 – miles to the Moon 1,000,000 – 10,000,000 – 100,000,000 – population of US -- miles to Sun 1,000,000,000 – pop of world 10,000,000,000 – years… ever… 100,000,000,000 – stars in Milky Way? Speed of Light 186,000 miles per second 300,000,000 meters per second (corrected number – there was a typo!) The Astronomical Unit The distance from the Earth to the Sun 93,000,000 miles = 150,000,000 km or 150,000,000,000 meters Constellations (and Asterisms) 88 recognized Constellations -- as seen from the Earth Angular Size The circle is divided into 360º Each 1º is divided into 60’ (minutes) Each 1’ is divided into 60” (seconds) 3600” = 1º and 1,296,000” = 360º Same Angle: Kepler’s Model with exaggerated ellipses Kepler’s Laws 1st Law: Planetary orbits about the Sun are ellipses and the Sun lies at one of the foci of the ellipse. 2nd Law: A line connecting the Sun and planet sweeps out equal areas in equal times. 3rd Law: p2(years) = a3(AU) p = period (time to go around once) a = semi-major axis (half of the long side of an ellipse) An Ellipse The Eccentricity of an ellipse tells you how stretched out it is. A circle is a special case of an ellipse with an eccentricity = 1. Planetary orbits turn out to be pretty close to circular… but just elliptical enough to matter. Because orbits are Elliptical, there are two important points in an orbit: apogee and perigee ap·o·gee (ăp¹ə-jē) noun 1. a. The point in the orbit of the moon or of an artificial satellite most distant from the center of the earth. b. The point in an orbit most distant from the body being orbited. French apogée, from New Latin apogaeum, from Greek apogaion, from neuter of apogaios, far from the earth : apo-, apo- + gaia, earth.] — ap´o·ge¹an (-jē¹ən) adjective per·i·gee (pĕr¹ə-jē) noun 1. The point nearest the earth's center in the orbit of the moon or a satellite. 2. The point in any orbit nearest to the body being orbited. [French périgée, from Medieval Latin perigēum, from Late Greek perigeion : Greek peri-, peri- + Greek gē, earth.] — per´i·ge¹al (-jē¹əl) or per´i·ge¹an (-jē¹ən) adjective About the Sun: aphelion and perihelion a·phe·li·on (ə-fē¹lē-ən, ə-fēl¹yən) noun plural a·phe·li·a (-lē-ə) The point on the orbit of a celestial body that is farthest from the sun. [From New Latin aphēlium : Greek apo-, apo- + Greek hēlios, sun.] per·i·he·li·on (pĕr´ə-hē¹lē-ən, -hēl¹yən) noun plural per·i·he·li·a (-hē¹lē-ə, -hēl¹yə) The point nearest the sun in the orbit of a planet or other celestial body. [Alteration of New Latin perihēlium : peri- + Greek hēlios, sun.] — per´i·he¹li·al (-hē¹lē-əl, -hēl¹yəl) adjective Motion Position – where you are Speed – a change in position Direction – where you are heading Acceleration – a change in speed and/or direction Mass – how much stuff you are Weight – mass under gravity Momentum – mass times speed The only way to change your momentum is to use a Force. Newton’s Laws The Zeroeth Law: There is such a thing as mass. The First Law: An object in motion tends to stay in motion, or an object at rest tends to stay at rest, unless acted upon by a net external force. The Second Law: F = m a Force = mass × acceleration The Third Law: For every action (force) there is an equal and opposite action acting on the other object. A pushes on B, so B pushes on A How Do We Know It Is So? Observation Hypothesis Theory Testing (Refinement) Most people don’t use the word “theory” to mean what it means in science. As a result, many arguments about “theories” don’t make any scientific sense.