Kepler's Laws lab

1) Tie the ends of the string into a loop about 6 - 7 cm across. 2) Mark two dots 0.5 cm apart in the center of one sheet of paper. 3) Put the paper over the cardboard, and push the thumbtacks into the points, far enough to be firm, but not flat against the paper. These are the ellipses foci. ................
................