TOPIC 4 REVIEW This topic is about what we can see occurring in our sky when we stand on Earth Or rather, our CELESTIAL SPHERE In the sky, almost all objects seem to move from EAST to WEST EXCEPT: POLARIS (THE NORTH STAR) WHY? Therefore, in a single evening, objects seem to move around Polaris. The proof is in the STAR TRAIL PICTURES: So how can we figure out how long the shutter in this camera was left open for? The Earth spins 360 in 24 hours OR = 15 PER HOUR. If we could measure the length of the arc, we could know how long the shutter of the camera was open for. ANIMATION Planets also move from E->W, but occasionally, they do strange things They move from E_>W, STOP, REVERSE COURSE (!), STOP AGAIN, then head back to their normal path. Are they lost? Drunk? Possessed by the devil? NO- they are exhibiting: RETROGRADE MOTION The Sun shows the greatest variation in motion. Imagine this is you, looking out a south-facing window, each day at noon. East is left, west is right. In our hemisphere, the sun rises due east on: MARCH 21 ST AND SEPT 21 ST These are called the EQUINOXES (autumnal and vernal) In our hemisphere, the sun rises NORTH of east on: JUNE 21ST This is the SUMMER SOLSTICE (note the highest path!) In our hemisphere, the sun rises SOUTH of east on: DECEMBER 21ST This is the WINTER SOLSTICE (note the lowest path!) ANIMATION So where is the sun directly overhead? Examine historical evidence and see if you can tellthese paintings were placed in the same location in all 4 seasons. See how direct the rays of the sun hit near where these were painted. What day is the picture seen below? NOTE: the vertical (90) rays of the sun are on the TROPIC OF CANCER This is the SUMMER SOLSTICE Note the North Pole always in light! What day is the picture seen below? NOTE: the vertical (90) rays of the sun are on the TROPIC OF CAPRICORN This is the WINTER SOLSTICE Note the North Pole always in darkness What day is the picture seen below? NOTE: the vertical (90) rays of the sun are on the EQUATOR This is the EQUINOX Note the North Pole right on the border between light & dark In order to explain what they saw, scientists came up with a model of the universe that had everything orbiting around the Earth: THE GEOCENTRIC MODEL = EARTH = AT CENTER However, there were several things that their model could not explain. 1.) RETROGRADE MOTION They dealt with this by adding mini-orbits (epicycles) onto the main orbits of the planets around the Earth. However, this only helped in the short-term. They had to keep adding epicycles on TOP of epicycles to explain where the planets would be in their orbits! However, there were several things that their model could not explain. 2.) THE FOUCAULT PENDULUM A pendulum that slowly turns as it swings. However, there were several things that their model could not explain. 3.) THE CORIOLIS EFFECT The fact that fluids are curved as they move to the RIGHT in the Northern Hemisphere, to the LEFT in the Southern Hemisphere. In order to accommodate those problems, a new idea was conceived: THE HELIOCENTRIC MODEL = AT CENTER = SUN The bizarre motions were now explained by the ROTATION OF THE EARTH EXPLANATION OF CORIOLIS EXPLANATION OF FOUCAULT PENDULUM EXPLANATION OF RETROGRADE MOTION The moon has chaotic motions as welland depending on where it is as it revolves around Earth, it creates the PHASES OF THE MOON How to determine phase: What phase of the moon is seen below? ECLIPSES occur when a solar system body moves into the shadow of another one. LUNAR ECLIPSE: The moon moves into the shadow of the Earth. SOLAR ECLIPSE: The Earth moves into the shadow of the Moon, blocking the sun. (can be partial, or total) What Phase? Why dont we get a solar eclipse every single time the new moon phase occurs? Moons orbit is TITLED 5 from the orbit of the earth so only rarely does it block the sun.