Careful measurements reveal that the earth has a slight difference in its dimensions EUREKA!!! COPY EARTH’S SHAPE? •The shape of the earth is technically called an OBLATE SPHEROID: •Slightly flattened at the poles and bulging in the middle(equator) EXAGGERATED PICTURE! COPY BUT….. IT LOOKS PERFECTLY ROUND TO US! OBLATE SPHEROID check this out!!! IT’S DRILL TIME!!!!! Polar Equatorial Circumference Circumference Polar Equatorial diameter Diameter Actual Numbers • Polar diameter • Equatorial diameter = 12,714km = 12,757km (7882mi) (7909mi) • Polar • Equatorial Circumference Circumference = 40,076km = 40,006km (24,847mi) (24,804mi) MODEL COPY •A MODEL is a way of representing the properties of some object – (Drawing, diagram, graph, chart, photo, table) Evidence for the Earth’s Shape: • 1. Altitude of Polaris • 2. Gravity Measurements • 3. “Sinking” ships • 4. Lunar Eclipses * POLARIS= NORTH STAR NORTH POLE Earth’s AXIS of Rotation Geographic Poles SOUTH POLE WHAT ABOUT THE SOUTH POLE? • At the present time, Polaris is the pole star in the northern direction. Sigma Octantis is the closest star to the south celestial pole, but it is too faint to serve as a useful pole star. The Southern Cross constellation functions as an approximate southern pole constellation. Some people travel to the equator in order to be able to see both Polaris and the Southern cross. Pointer Stars! POLARIS Polaris is found in the little dipper!! COPY COPY Detailed Evidence for the Earth’s Shape COPY 1. Altitude of Polaris: The altitude is the ANGLE above the horizon Polaris is directly over the North Pole (Fixed Star) Your LATITUDE (degrees North or South of equator) equals ALTITUDE of POLARIS! 90O 30O 0O Person standing at 30ON POLARIS 90O 45O 0O 2. Gravity Measurements COPY Gravity is a force affected by mass and Distance from center of earth As the distance from center of earth increases, your weight decreases (equator) WEIGH MORE WEIGH LESS X Center of earth! 3. Sinking ships: COPY As ships sail toward the horizon, they appear to “sink” over the horizon Curved Earth 4. Polaris: COPY As you head NORTH towards the North Pole, Polaris appears higher and higher in the sky That’s far out!!! 300 light years from Earth, or about 3000 trillion km = 3,000,000,000,000,000 km = 1860 trillion miles = 1,860,000,000,000,000 miles POLARIS---Stays still COPY Earth's AXIS makes one complete wobble every 26,000 years! What star is next? During the past 5000 years the axis has pointed at the star Thuban (Alpha Draconis) In the year 7500 the North Star will be Alpha Cephei In the year 15,000 it will be the star Vega. About 9000 years after that, Polaris will again become the North Star. 5. Lunar Eclipse: COPY During eclipse, shadow of earth that is cast on moon is in the shape of arc MOON Earth’s shadow Blood red total Eclipse Lunar Eclipses THINK GRAVITY! (Affected by distance!) WEIGH WEIGH SLIGHTLY SLIGHTLY MORE! LESS CLOSER! FARTHER! CENTER OF EARTH!.