um i need too make a program for school for extra credit but i am stumped. this is the directions i was given.

make 1 large yellow circle(the sun) then make one small blue circle(earth) make the small circle orbit around sun in an eliptical orbit.
also make 100 stars apear at random when the program is started. i have no clue how to make the circle orbit i was given this equation by a kid who said i eed to use it but i dont know

b^2 (x-k)^2 + a^2 (y-k)^2 = a^2 b^2

any heelp would be much appreciated.

i would take time to figure all out my self but i dont do this extra credit i will fail class .
thank you for help