T/G Layout 1

epler laws of motion

1. A planet moves about the Sun in an elliptic orbit, with one focus of the ellipse

located at the Sun.

2. A straight line from the Sun to the planet sweeps out equal areas in equal times.

( f i g u re 55b).

3. The time re q u i red for a planet to make one orbital circuit, when squared, is pro -

p o rtional to the cube of the major axis of the orbit (figure 55c).

Sun

2a

major axis

a

semi-major axis

a x e

Sun Focus

semi-minor

axis

K

f i g u re 55.

a.

b.

c.