Mathematics and Society - OS X Lion Server

t~£p'KEPLER- DIDNTGO AeOUNDIN CU2CLESIn studying Tycho Brahe's observations of theplanets, Kepler discovered that the orbits of theplanets were not circles, but ellipses.You can draw ellipses of different sizes andshapes.PLAtJET(Materials:A piece of heavy cardboard (20 cm x 30 cm),2 thumbtacks, a piece of string (40 cm)1. Place the thumbtacks in the cardboardabout 5 cm apart. Knot the ends ofthe string and loop it around thetacks.2. Put the point of your pencil insidethe loop and pull the string taut.Draw a figure by moving your pencilin a clockwise direction, keepingthe string taut at all times. Thefigure you just drew is an ellipse.3. Draw several other ellipses usingthe same loop, but with the tacksdifferent distances apart.mcesFOCI