AST 100 Exam 1 Study Guide PDF

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AST 100 Exam 1 Study Guide

celestial sphere ecliptic, sideral day and solar day ecliptic apparent path of sun over 1 year sidereal day lasts for 23 hours and 56 mins solar day lasts for 24 hours seasons caused by elliptical orbit and tilted axis tilted axis circular - depending on whether the tilt is facing the sun or not, is the season elliptical orbit an oval shaped path the earth takes around the sun or the moon takes around the earth phases of the moon new moon - first quarter - full moon - third quarter new moon to new moon? 29 days angular diameter apparent size is an angular measurement describing how large a sphere or circle appears from a given point of view angle units degrees, arc-minutes, arc-seconds degrees 360 degrees = 1 circle 1 degree is approximately the angular width of a finger at arm's length angular diameter of moon is 1/2 degrees

arc minutes 1 degree = 60' 1' is approximately the resolution of the human eye arc-seconds 1' = 60" 1" is approximately the resolution to blowing by the earth's atmosphere eclipses solar, lunar solar eclipse moon passes in front of the sun only lasts 2-4 minutes seen by 1-2% of earth shows that the moon is always closer than the sun and the moon and sun have the same angular diameter lunar eclipse moon passes through earth's shadow lasts 2-4 hours seen by 1/2 of earth shows that the earth is spherical earth is approximately 4x the size of the moon can only occur during a full moon aristotle argued earth could not spin or move (both wrong) aristarchos relative sizes and distances of the sun, moon and earth small angle equation W = θ° d/57.3 motions of the starts, sun, moon and planets sun, moon & planets drift against “fixed” pattern of stars moon moves W to E around sky every month sun moves W to E around sky every year mercury and venus move back and forth motion centered on sun Jupiter moves W to E around sun every 12 yrs Saturn moves W to E around the sun every 30 yrs ptolemy's geocentric model deferents and epicycles

copernicus' heliocentric model (still uses circles) the retrograde loops are an illusion created by moving earth galileo's discoveries sunspots, mountains on moon, jupiter's moons, phases of venus, "new stars" post renaissance did not invent the telescope - first person to use the telescope for astronomy Kepler's three laws of planetary motion astronomical unit (AU) 2 equal area is swept out in equal time by a line connecting a planet to the sun the square of the orbital period (P) and the cube of the semi-major axis (A) are in a fixed ratio for all planets Astronomical Unit earth's semi-major axis avg. earth-sun distance = 93,000 miles 2 equal area is swept out in equal time by a line connecting a planet to the sun equal area and time law the square of the orbital period (P) and the cube of the semi-major axis (A) are in a fixed ratio for all planets if = measure P in years and measure A is AU then: P equared divided by A cubed equals 1 A bigger orbit (A) will have a longer period (P) mass the amount of material in that object not size and not weight velocity an objects speed and direction acceleration any change in velocity with time newtons laws of motion (F=ma) 1. the velocity of an object is unchanged unless acted upon by a net external force 2. the acceleration of an object is equal to the force acting on it divided by the mass of the object, and acceleration in the direction of the force newton's law of gravity F = GM1M2/R2

gravitational acceleration a1=GM2/R2 a2=GM1/R2 Gravitational Tides; examples of effects 1. moons spin-orbit resance 2. earth’s ocean tides 3. day on earth vary slowly getting longer 4. rings of outer planets - rings can decay into the planet (10 million yrs) 5. heating of Jupiter and saturns moons Jupiter: IO – volcano world - Europa: oceans under ice...