Question

1. Which object (planet or star) takes a greater amount of time to complete one orbit? Explain.

        a. If the extrasolar planet is orbiting counterclockwise, what direction does the star orbit, clockwise or counterclockwise?

        b. Which letter, A, B, or C indicates the center of mass of the system?

        c. At a certain instant of time, how does the direction the extrasolar planet is orbiting compare to the direction the star is orbiting?

        d. In Figure 2, if the planet is orbiting counterclockwise, which direction is the planet moving, towards or away from us? Which direction is the star moving, towards or away from us?

с в А CBA Figure 1-extrasolar planet orbit seen from above Figure 2-extrasolar planet orbit seen nearly edge-on

Answer 1

Both, the star and the sun, take the same amount of time to complete one one orbit because they orbit the berycenter(center of mass of both). The berycenter is a fixed point. Since the line which connects the planet and the star has to pass through the berycenter, for that they have to complete the orbit in exact same time.

Hence they take same amount of time to complete an orbit.

(A) again we can say that the line connecting the star and the extra solar planet, has to pass through the Barycentre at every point of time for that to happen they have to b exactly opposite to each other so if the extra solarplanet is orbiting counterclockwise it means that the star is orbiting in clockwise direction.

(B).

The centre of mass of both of the bodies has to be inside the orbit of both, so letter A indicates the centre of mass of the system.

(C)

At every instant of time the direction of orbit extrasolar planet is opposite to the direction of the orbit of star.

(D)

We are at the location mentioned in Figure 2 then we will find that the extrasolar planet is moving towards us while the star is moving away from us.