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Nicholas Copurnicus [email protected] astro1010-lee.com Survey of Astronomy Chapter 3 Wanderers (Planets) Inferior Nearer the Sun than the Earth Morning Star/Evening Star Superior Farther from the Sun than the Earth Loops [email protected] astro1010-lee.com Survey of Astronomy Chapter 3 Movement of Mars [email protected] astro1010-lee.com Survey of Astronomy Chapter 3 Motion of the Sun Moon [email protected] astro1010-lee.com Survey of Astronomy Chapter 3 Ptolemy’s explanation [email protected] astro1010-lee.com Survey of Astronomy Chapter 3 Glory Years of Astronomy [email protected] astro1010-lee.com Survey of Astronomy Chapter 3 Motion of Mars by Copurnicus [email protected] astro1010-lee.com Survey of Astronomy Chapter 3 Galileo Galilei Outstanding scientist of his era Bought and built telescopes Observed Venus in gibbous phase moons around Jupiter millions of stars in the Milky Way spots on the Sun craters, highlands and seas on the Moon etc. [email protected] astro1010-lee.com Survey of Astronomy Chapter 3 Venus by Ptolemy Venus by Copunicus [email protected] astro1010-lee.com Survey of Astronomy Chapter 3 Tycho Brahe Invented wonderful observing tools Twenty years of observations Hired Kepler [email protected] astro1010-lee.com Survey of Astronomy Chapter 3 The Solar system by Tycho astro1010-lee.com Survey of Astronomy Chapter 3 [email protected] Kepler’s 1st Law Every Planet revolves around the Sun in an orbit that is an ellipse with the Sun at one focus [email protected] astro1010-lee.com Survey of Astronomy Chapter 3 Kepler’s 2nd Law A line from the planet to the Sun will sweep out equal area in equal time [email protected] astro1010-lee.com Survey of Astronomy Chapter 3 The square of the period of a planet is equal to the cube of the semi-major axis Kepler’s 3rd Law 2 3 P=a Yr AU [email protected] astro1010-lee.com Survey of Astronomy Chapter 3 Sir Isaac Newton Newton was a genius whose work in mathematics, theoretical mechanics and optics completely revolutionized physics [email protected] astro1010-lee.com Survey of Astronomy Chapter 3 Gravity Every object anywhere in the Universe attracts every other object in the Universe by a Force which Mm F=G r2 is proportional to the product of their masses and inversely proportional to the distance separating them. [email protected] astro1010-lee.com Survey of Astronomy Chapter 3 Gravity The equation for the intensity of light has a similar form to the gravity equation so we can use light to demonstrate the Inverse Square Law. Inverse Square Law [email protected] astro1010-lee.com Survey of Astronomy Chapter 3 Laws of Motion Newton’s 1st Law Newton’s 1st Law A body at rest will remain at rest and a body in motion will remain in motion in a straight line until acted upon by a force. In the absence of a force the velocity (V) will not change [email protected] astro1010-lee.com Survey of Astronomy Chapter 3 Laws of Motion Newton’s 2nd Law The acceleration of a body is proportional to the force applied and inversely proportional to the mass of the body. F=ma Newton’s 2nd Law The change of velocity = acceleration (a) = Force / mass a = F/m [email protected] astro1010-lee.com Survey of Astronomy Chapter 3 Laws of Motion Newton’s 3rd Law For every action there is an equal and opposite reaction m1 v 1 = m 2 v 2 astro1010-lee.com Survey of Astronomy Chapter 3 From this law we derive Thrust which makes possible Jet Engines and Rockets [email protected] Orbital Mechanics Knowing that a bullet shot out of gun is pulled to the ground by gravity, Newton envisioned this experiment on the top of the highest mountain. From this experiment Newton related the motion of the Moon to the motion of a falling apple. [email protected] astro1010-lee.com Survey of Astronomy Chapter 3 Orbital Mechanics An object is space has a velocity. During a given time the object would move from A to B. But in the same time the gravity from the sun causes it to fall toward the sun the distance from A to D. The resulting trajectory of the object is from A to C. If the object is a planet in orbit we note that the distance from C to the Sun is just the same as the distance A to the Sun. [email protected] astro1010-lee.com Survey of Astronomy Chapter 3 Kepler’s 3rd Law as Modified by Newton Newton discovered while working from ‘first principles’ that Kepler’s 3rd Law needed to be modified. Leaving out constants… 2 (M1+M2) P = a 3 Masses must be measured in Solar masses, period in Earth years and the distance between masses in Astronomical Units [email protected] astro1010-lee.com Survey of Astronomy Chapter 3 Tides Many books explain tides this way. Moon pulls on the water on the Moon side causing it to bulge up a little. The Moon pulls the center of the Earth away from the water on the far side causing it bulge up a little on that side. [email protected] astro1010-lee.com Survey of Astronomy Chapter 3 Tides (an alternate explanation) The Earth and the Moon revolve around the common center of mass for the system (Barycenter). The tide one Moon side is due to gravitational force but the tide on the other side is due to centrifugal force. Barycenter [email protected] astro1010-lee.com Survey of Astronomy Chapter 3 End Chapter 3 [email protected] astro1010-lee.com Survey of Astronomy Chapter 3