Kepler's Laws

According to Kepler's first law, planets orbit the sun in the shape of an ________

The easiest way to draw an ellipse is to put two tacks in a piece of paper and put a loose loop of a string around them, as shown in the figure below.

If the tacks are placed farther apart, how will the shape of the ellipse be changed?

The easiest way to draw an ellipse is to put two tacks in a piece of paper and put a loose loop of a string around them, as shown in the figure below.

What would the positions of the tacks have to be to draw a circle?

As a planet orbits the sun, a line from the planet to the sun sweeps across equal areas in equal times.