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What is the difference between rotation and revolution? 2. What causes the seasons? 3. True/False: The Earth has an axial tilt. 1. Objective: Understanding how the Sun, Earth and Moon move relative to one another and how they affect each other. Axis – an imaginary line around which an object spins; 23.5° Aristotle 350BC, knew the world was round due to Earth always casting a round shadow during an eclipse Apparent Motion – what seems to be happening Real Motion – what really is happening 1. Sun rises in the East and sets in the West 1. Earth is rotating on its axis 2. Sun and stars travel in an arc across the sky 2. Earth is rotating 3. Moon appears and disappears in 3. Moon revolves around (orbits) phases the Earth 4. Earth changes temperature with 4. Earth orbits the sun and is tilted seasons 23.5° 5. Solar day is 24 hours 5. Actual day 23 hours 56 minutes 4 seconds. Shorter than 24 hours because of Earth’s revolution around the sun. Rotation Revolution • Turning/spinning of Earth on it’s axis • Movement of Earth and planets around the Sun • Path of revolution is one orbit • Once every 24 hours (approximately) • Once every year (approximately) Causes: Causes: • Celestial bodies appear to move in an arc across the sky • Change in duration of sunlight at different latitudes • Length of day (24 hours) • Changes in temperature with seasons (along with tilt) • Direction of sunrise (East) and sunset (West) • Change in angle of sunlight at different latitudes (tilt) • Coriolis Effect (bending of winds and ocean currents) Winter Solstice Summer Solstice • Northern hemisphere is tilted away from the Sun • December 21st • Sun shines directly on Tropic of Capricorn • Longest hours of darkness • Northern hemisphere is tilted towards the Sun • June 21st • Sun strikes Earth at an angle of 90 degrees at the Tropic of Cancer • Long hours of daylight **The hemisphere tilted towards the sun receives the most radiation and more daylight hours** Spring (Vernal) Equinox Fall (Autumnal) Equinox March 21st September 23rd Equinox – days when the amount of sunlight and darkness is EQUAL; sun is directly over the equator Reasons for Seasons Caused by differences in absorbed solar energy due to Earth’s axial tilt and revolution around the Sun Reasons for Length of Day Axial tilt Tilted away from the Sun = less time facing the Sun = shorter day Tilted towards the Sun = more time facing the Sun = longer days Ellipse – a closed curve around 2 fixed points known as foci; path of the Earth Aphelion (apogee) – point where Earth is farthest from the Sun (July 4th) Perihelion (perigee) – point where Earth is closest to the Sun (January 2nd) 1. Orbits of the planets around the sun are ellipses, with the sun at one of the foci. 2. An imaginary line joining planet to the sun will sweep out equal areas in equal periods of time. 3. The father a planet is from the sun, the longer its year. Geocentric Model Heliocentric Model • Earth at the center of the solar system • Sun at the center of the solar system Explains: Explains: • Daily motions of sun, planets and stars in the sky • Retrograde motion or “backing up” of planets in the sky (due to farther planets moving slower) • Sort of explains why some planets appear to “back up” in their path across the sky (retrograde motion) • Apparent diameter changes of moon and planets • Phase changes of Venus Accepted model of the solar system Proof: Foucault Pendulum: path changes due to rotation of the Earth Coriolis Effect: deflection of objects to the right in the Northern Hemisphere due to Earth’s rotation A major misconception is that the seasons are caused by the Earth being closer to the Sun in the summer and farther from the Sun in the winter due to Earth’s elliptical orbit. Explain why this idea is a misconception. What really causes winter in the Northern Hemisphere and summer in the Northern Hemisphere?