Modern Day Astronomers (sort of) The New Guys

The Astronomers Copernicus Galileo Tycho Brahe Johannes Kepler Sir Isaac Newton

Copernicus O Life: O Theory: O Reintroduced the heliocentric model of the Universe Proof? The New Guys

Proof? O 7 points 1. Earth is not the center of everything 2. Earth is only the center of gravity and of the lunar orbit 3. All planets revolve around the Sun 4. The stars are much farther away than the Sun 5. Apparent motion we see in the stars is due to the movements of the Earth Proof Cont’dCopernicus

Proof? Cont’d O 7 points 6. The Sun’s daily and yearly motion are due to the Earth’s rotation and revolution around the Sun 7. The Sun-centered model provides a natural explanation for the retrograde motion of the planets, which is again caused by the movement of the Earth Copernicus

Galileo O Life: 1564 – 1642 O Contributions: O One of the first to turn a telescope to the heavens O First to see the moons of Jupiter O Recognized that his observations conflicted with Ptolemic views The New Guys Galileo’s Work Joke

Galileo’s Tracking of Jupiter's Moons Galileo

Tycho Brahe O Life: O Known For: O Made the most extensive observations with just the naked eye. O He noticed errors in the Ptolemic planetary tables O Had his own semi- heliocentric theory of the solar system Man with the Golden Nose The New Guys Theory

Brahe

Johannes Kepler O Life: O Known for: O Used Brahe’s observations to develop three laws of planetary motion = Kepler’s laws The New Guys 1 st Law 2 nd Law 3 rd Law

Kepler’s 1 st Law O Each planet moves in an ellipse with the Sun at one focus O An ellipse is an elongated circle- O with two foci -a point around which the planet revolves, O a line drawn through both foci and including the orbit is known as the major axis O ½ this distance is known as the semi-major axis (the average distance from the Sun) KeplerImageKepler’s 1 st Law cont’d

Kepler’s 1 st Law

Kepler’s 1 st Law O Eccentricity O is the ratio of the distance between the foci to the length of the major axis (or diameter) O A circle is an ellipse whose eccentricity is zero O Using the semi-major axis and the eccentricity: O Perihelion: closest point to the Sun O Aphelion -a planets farthest point from the Sun (ap- think away) KeplerImageCartoon

Kepler Kepler’s 1 st Law

Kepler

Kepler’s 2 nd Law O The line between the Sun and the planet sweeps out equal areas in equal time intervals O Planets move fastest when closest to the Sun ImageKepler

Kepler’s 2 nd Law

Kepler’s 3 rd Law O “Harmonic Law” O The time it takes for a planet to complete one period (a planetary year) is equal to the square root of the semi-major axis cubed O p 2 = a 3 Kepler

Newton O Kepler knew the how but not the why of planetary motion O It took Isaac Newton to explain why all objects interact the way that they do The New Guys Laws of MotionLaw of Gravity Planetary Motion Correcting Kepler

Newton Laws of Motion 1. A body at rest stays at rest unless acted upon by an outside force, a body in motion stays in motion unless acted upon by an outside force 2. Force is equal to mass times acceleration F = ma 3. For every action there is an equal and opposite reaction- this means that you attract the Earth with exactly the same force as it attracts you- also explains how a rocketship is propelled Newton

Newton’s Laws of Gravity O F = Gm 1 m 2 r 2 O F = force O G = constant 6.67 x Nm 2 /kg 2 O M 1 = mass of body #1 O M 2 = mass of body #2 O R = radius between two bodies O Force of gravity for Earth = 9.8 m/s 2 Newton

Planetary Motion O So why doesn’t Earth fall into the Sun? O A combination of gravitational forces of both bodies and our planet’s velocity Newton

Correcting Kepler’s Laws O The orbit of a planet around the Sun is an ellipse with the common center of mass of the planet and the Sun at one focus Newton