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Actual Motions of Earth Models that Help Explain Apparent Celestial Motions • Geocentric model- Earth is stationary in the center of the universe and all celestial objects revolve around it. • Heliocentric model- the sun is the center of the solar system and all parts revolve around it. Answer the questions on your notes near the explanation of each model. Geocentric system Actual Earth Motions • Rotation- the spinning of Earth on its axis, the imaginary line that runs from the north pole to the south pole. – Earth’s axis is tilted 23 ½ ° with the northern end pointing toward the North Star (Polaris). – Earth rotates west to east (counterclockwise) – Causes daily motion of celestial objects like sun, moon & stars Actual Motion of the Earth Rotation Evidence of Earth’s Rotation 1. The Foucault Pendulum- a freely swinging pendulum whose path appears to change in a predictable way (if the Earth didn’t rotate, it would swing in the same way) Great info Evidence of Earth’s Rotation 2. The Coriolis Effect- the tendency of all particles of matter moving at Earth’s surface to be deflected, or curve away, from a straight line path. – Deflection is to the right in the Northern hemisphere – Deflection is to the left in the Southern Hemisphere . Actual Earth Motions • Revolution- a planet’s movement around the sun in a path called an orbit (the movement of one body around another). – Causes seasonal motion of celestial objects, like sun & constellations – The planets revolve counterclockwise around the sun as seen from Earth’s north pole. Actual Motion of the Earth Revolution Evidence of Earth’s Revolution Around the Sun • Seasons - If Earth didn’t revolve around the sun, the same part of Earth would be tilted toward the sun and receive the more direct rays. THE SEASONS WOULD NOT CHANGE. – Summer is when we tilt toward the sun & the sun is higher in the sky – Winter is when we tilt away from the sun & the sun is lower in the sky • Constellations - groups of stars that form a pattern – We see different constellations at different times of the year. Reasons for the Seasons Reasons for the Seasons Evidence of Earth’s Revolution Around the Sun Constellations Which constellations are both visible at midnight to an observer in Virginia when Earth is located at position D? 1. Aries & Taurus 2. Pisces & Libra 3. Leo & Virgo 4. Aquarius & Scorpio Retrograde Motion - Ptolemy When the planets move backwards in the sky Very difficult to fit retrograde motion into geocentric view – requires planets to travel in circles on circles Retrograde Motion - Actual In actuality, in a heliocentric view, Earth is simply passing or being passed by other planets, creating the odd backwards movement http://www.lasalle.edu/~smithsc/Astronomy/retrograd.html Earth’s Motions • Rotation – Polaris http://ecuip.lib.uchicago.ed u/diglib/science/cultural_ast ronomy/interactives/polaris/ polaris.swf • Revolution – Seasons http://astro.unl.edu/classact ion/animations/coordsmotio n/eclipticsimulator.html – Direct/Indirect rays http://astro.unl.edu/classact ion/animations/coordsmotio n/sunsrays.html – Motion of Sun http://astro.unl.edu/classact ion/animations/coordsmotio n/sunmotions.html Motion of Celestial Objects Review 1. What two motions of the Earth cause the apparent motion of celestial objects? 2. What is one proof for each of these motions? Indicate which is which. 3. When is the altitude (height) of the sun higher or lower?
