Presentation on theme: "Astronomy Notes to Accompany the Text"— Presentation transcript:
1 Astronomy Notes to Accompany the Text Astronomy Today, Chaisson, McMillanJim Mims
2 The Copernican Revolution Chapter 2The Copernican Revolution
3 Units Ancient Astronomy The Geocentric Universe The Heliocentric Model of the Solar SystemThe Foundations of the Copernican RevolutionThe Birth of Modern Astronomy
4 Units, cont. The Laws of Planetary Motion Some Properties of Planetary OrbitsThe Dimensions of the Solar SystemNewton’s LawsThe Moon Is Falling!Weighing the Sun
5 Ancient Astronomy Ancient civilizations observed the skies Many built structures to mark astronomical eventsSummer solstice sunrise at Stonehenge:
6 Ancient AstronomySpokes of the Big Horn Medicine Wheel are aligned with rising and setting of Sun and other stars:
7 Ancient AstronomyThe temple at Caracol has many windows that are aligned with astronomical events
8 The Geocentric Universe Ancient astronomers observed:SunMoonStarsFive planets: Mercury, Venus, Mars, Jupiter, Saturn
9 The Geocentric Universe Sun, Moon, and stars all have simple movements in the skyPlanets:move with respect to fixed starschange in brightnesschange speedhave retrograde motion
10 The Geocentric Universe Inferior planets: Mercury, VenusSuperior planets: Mars, Jupiter, SaturnNow know:Inferior planets have orbits closer to Sun than Earth’sSuperior planets’ orbits are farther away
11 The Geocentric Universe Early observations:Inferior planets never too far from SunSuperior planets not tied to Sun; exhibit retrograde motionSuperior planets brightest at oppositionInferior planets brightest near inferior conjunction
12 The Geocentric Universe Earliest models had Earth at center of solar systemNeeded many computations to accurately track planetary motions:
13 The Heliocentric Model of the Solar System Sun is at center of solar systemOnly Moon orbits around Earth; planets orbit around Sun
14 The Birth of Modern Astronomy Telescope invented around 1600Galileo built his own, made observations:Moon has mountains and valleysSun has sunspots, and rotatesJupiter has moons:Venus has phases
15 The Birth of Modern Astronomy Phases of Venus, in particular, cannot be explained by geocentric model
16 The Laws of Planetary Motion Kepler’s laws, derived using observations made by Tycho Brahe:
17 The Laws of Planetary Motion 1. Planetary orbits are ellipses, Sun at one focus
18 The Laws of Planetary Motion 2. Imaginary line connecting Sun and planet sweeps out equal areas in equal times
19 The Dimensions of the Solar System Astronomical unit: mean distance from Earth to SunFirst measured during transits of Mercury and Venus, using triangulation
20 The Dimensions of the Solar System Now measured using radar:Ratio of mean radius of Venus’s orbit to that of Earth very well known
21 Newton’s LawsNewton’s laws of motion explain how objects interact with the world and with each other.
22 Newton’s Laws Newton’s First Law: An object at rest will remain at rest, and an object moving in a straight line at constant speed will not change its motion, unless an external force acts on it.
23 Newton’s Laws Newton’s second law: When a force is exerted on an object, its acceleration is inversely proportional to its mass:a = F/mNewton’s third law:When object A exerts a force on object B, object B exerts an equal and opposite force on object A.
24 Newton’s LawsGravityOn the Earth’s surface, acceleration is approximately constant, and directed toward center of Earth:
25 Newton’s LawsGravityFor two massive objects, gravitational force is proportional to the product of their masses divided by the square of the distance between them:
26 Newton’s LawsGravityThe constant G is called the gravitational constant; it is measured experimentally and found to be:G = 6.67 × 10–11 N m2/kg2
27 Newton’s LawsKepler’s laws are a consequence of Newton’s laws.
28 Newton’s LawsEscape speed: the speed necessary for a projectile to completely escape a planet’s gravitational field
29 SummaryFirst models of solar system were geocentric, but couldn't easily explain retrograde motionHeliocentric model does; also explains brightness variationsGalileo's observations supported heliocentric modelKepler found three empirical laws of planetary motion from observations
30 SummaryLaws of Newtonian mechanics explained Kepler’s observationsGravitational force between two masses is proportional to the product of the masses, divided by the square of the distance between them