Orbit of planets

1. Nov 2, 2008

dswatson

Mars orbits the sun at a mean orbital radius of 228e9 m and has an orbital period of 687 d. Earth orbits teh sun at a mean orbital radius of 149.6e9 m.
a)The earth-sun line sweeps out an angle of 360 degrees during one earth-year. Approximately what angle is swept out by the Mars-sun line during one Earth-year?
b) How frequently are Mars and the sun in opposition (on diametrically opposite sides of Earth)?

I do not know any relavant equations or even how to begin this problem we were given this homework as we walked out of the room without covering all of the necessary material.
Any help would be greatly appretiated. Thank you.

2. Nov 2, 2008

mgb_phys

A, is simply asking what proportion of a mars year is one earth year.

3. Nov 2, 2008

dswatson

so is it as simple as...

365.24d/360=687/x

then solve for x?

4. Nov 2, 2008

mgb_phys

Almost, 365.24/687 = x/360
A mars year is about twice an Earth year, so you should get an answer of about half a full circle

5. Nov 4, 2008

dswatson

just wanted to say thanks